Regulation of cell-mediated immunity in cryptococcosis. II. Characterization of first-order T suppressor cells (Ts1) and induction of second-order suppressor cells

Cryptococcosis patients frequently have high levels of cryptococcal antigen in their body fluids, and the levels of circulating antigen can generally be used to predict the patient's recovery, with high or rising antigen titers indicating a poor prognosis and low or decreasing levels a good prognosis. In a previous study, we reported on a murine model for studying the effects of cryptococcal antigen on host defense mechanisms. In that work, we demonstrated that an i.v. injection of cryptococcal antigen (CneF) into CBA/J mice, to simulate the antigenemia known to occur in human cryptococcosis, induced a population of T suppressor cells (Ts1) in the lymph nodes (LN). Upon adoptive transfer, the Ts1 cells specifically suppressed the afferent limb of the delayed-type hypersensitivity (DTH) response to cryptococcal antigen. In the present study, we show that the precursors of the Ts1 cells are sensitive to low-dose cyclophosphamide treatment and that the phenotype of the Ts1 cells is Lyt-1+, Ia+ (I-J+). LN cells from CneF-injected mice or a soluble factor derived therefrom can induce in the spleens of recipient mice a second-order suppressor cell population that suppresses the efferent limb of the DTH response. The cells that induce the second-order or efferent suppressor cells have the same phenotype as the cells that appear to suppress the afferent limb of the DTH response. The findings in this study indicate that a complex regulatory mechanism is responsible for the observed suppression of the DTH response in this infectious disease model. Furthermore, the suppressive circuit thus far defined for cryptococcal antigen is similar to the antigen-specific suppressor cell pathway outlined for certain chemically defined haptenic systems.     

Epidermal cells in activation of suppressor lymphocytes: further characterization

Intravenous administration of hapten-coupled, high-density (density greater than 1.077) epidermal cells (HD-EC) to mice results in the appearance of transferable splenic T suppressor (Ts) cells as assayed in adoptive transfer experiments. Depletion of I-A bearing cells from the HD-EC population before hapten coupling prevents these cells from inducing Ts cell formation, whereas depletion of Thy-1-bearing cells from the HD-EC cell preparation has no effect. When HD-EC are adhered to glass for 2 hr, the ability to induce Ts cell formation resides in the adherent population. Exposure of HD-EC to a dose of ultraviolet radiation (UVR) that largely abrogates the ability of hapten-coupled EC to immunize mice for a DTH response does not affect the ability of these cells to activate Ts cells. Treatment of mice with i.p. administration of 20 mg/kg of cyclophosphamide 2 days before EC harvesting abrogates the ability of HD-EC from these mice to induce Ts cell formation. HD-EC from B10.A(3R) (I-Jb) but not B10.A(5R) (I-Jk) mice induce Ts cell formation in B10.A(3R) mice, demonstrating that the ability to do so is restricted by the I-J locus. Transmission electron microscopy of adherent HD-EC populations demonstrated that two cell types were present. One type had the characteristics of keratinocytes; the other was monocyte-like and resembled Langerhans cells or indeterminate cells in many aspects. Immunoelectron microscopy revealed this second cell type to bear I-A/I-E antigen. These cells were T-200 positive and Mac-1 negative by immunoperoxidase staining. Extensive examination by light and electron microscopy failed to reveal any dermal components in the EC populations; however, a very small degree of dermal contamination cannot be excluded. Thus, EC that activate afferent-acting Ts cells are high-density, I-A+, Thy-1-, I-J restricted, glass adherent, and functionally UVR resistant and cyclophosphamide sensitive.     

Suppression of antigraft immunity by preimmunization. III. Characterization of suppressor T cells involved in suppression of the efferent phase of DTH against alloantigens

Suppressor T (Ts) cells that can suppress delayed type hypersensitivity (DTH) against histocompatibility (H) antigens can be isolated from spleen and lymph nodes a few days after i.v. immunization of mice with irradiated allogeneic spleen cells. In this paper we investigated the suppression of the efferent phase of DTH to characterize the Ts cells involved, and to compare them with the afferent phase Ts cells that have been characterized in a previous paper of this series. The DTH against third party alloantigens that were not used for the i.v. suppressive immunization could be suppressed by presenting the third party alloantigens together with the original alloantigens in the challenge inoculum for eliciting the DTH reaction. Thus the ultimate suppressive effect by the Ts cells that are active during the efferent phase of DTH is nonspecific. This non-specific suppression of DTH to alloantigens has previously been found for the afferent phase Ts cells as well. For suppression of the efferent phase of DTH to alloantigens, a population of Lyt-1+2+ Ts cells appeared to be essential, just like in the suppression of the afferent phase of DTH to alloantigens. We did not find evidence for the involvement of cyclophosphamide-sensitive auxiliary Ts cells in suppression of the efferent phase of DTH. Also no evidence was found for H-2 or Igh-restricted activation and function of the Ts cells that were active during afferent and efferent phases of the DTH response to H antigens. In view of these similarities between afferent phase and efferent phase Ts cells we conclude that there are no arguments as yet to suppose that there is more than one type of T cells involved in the suppression of the afferent and efferent limb of DTH against H antigens.     

Inhibition of the T suppressor circuit of delayed-type hypersensitivity by interferon

The effects of electrophoretically pure murine interferon (Mu-IFN-alpha beta) on the T suppressor pathway and on the T effector cell of delayed hypersensitivity (TDH) were investigated in BALB/c mice, in a 2,4-dinitrofluorobenzene (DNFB) contact-sensitivity model. Various T cell subpopulations, suppressor T cells of the afferent (Ts-aff) and efferent (Ts-eff) types, an auxiliary Ts (Ts-aux), as well as TDH were induced, and their function was assessed in transfer experiments. The results were as follows. At a dose of 5 X 10(3) U, IFN was shown to inhibit the Ts-aff response, when given to the donor animal shortly after induction of the Ts-aff subpopulation or when injected into the recipient 2 hr after spleen cell transfer. Pretreatment in vitro with IFN of the splenic cells to be transferred also abolished the Ts-aff response. Similar amounts of IFN were able to inhibit the generation of Ts-eff in the donor animals, whereas 10-fold-higher amounts were needed in vivo or in vitro to block the functional expression of Ts-eff in the recipient animal. Intravenous injection of IFN into recipients of Ts-eff on day 0 and 1 after sensitization inhibited the expression of the Ts-eff transferred 1 day before ear challenge. This suggests that the Ts-aux response required for the TDH suppression by Ts-eff is blocked by IFN. Secretion of a suppressor factor by Ts in vitro was not blocked by IFN. Treatment of the donor of suppressor factor-secreting Ts with IFN, however, blocked the induction of this Ts. The TDH were not sensitive to IFN even at amounts approximately 100 times higher than those used for the Ts inhibition in vivo as well as in vitro. These results demonstrate that low amounts of IFN may selectively block the suppressor pathway, because induction of these regulatory T cell subsets appears to be particularly sensitive to IFN. The exact mechanism of the IFN-mediated inhibition of Ts is not yet clear. The data suggest an important regulatory function of IFN in delayed-type hypersensitivity (DTH) reactions.     

In vivo priming of helper and suppressor T cells by alloantigens. Frequency analysis with the use of an in vitro limiting dilution assay

Earlier studies have demonstrated that T cells activated in mixed lymphocyte reactions can exert positive as well as negative allogeneic effects on B cells expressing the appropriate alloantigens on their surface. We investigated the effect of in vivo priming of T cells with alloantigens on their capacity to help or suppress allogeneic B cell cultures against sheep erythrocytes. We used immunization protocols that have been shown to be optimal for induction of alloantigen-specific delayed-type hypersensitivity (DTH) and alloantigen-specific suppressor T (Ts) cells for DTH. The results show that in vivo stimulation with alloantigens, depending on the immunization route and the lymphoid organ studied, can be as effective as in vitro stimulation in increasing the frequency of alloantigen-specific helper T (Th) cells and Ts cells. Subcutaneous immunization induced a 10-fold frequency raise of Th cells as well as of Ts cells in the lymph nodes. In the spleen the Th cell population was hardly affected by s.c. immunization, whereas the Ts cell population increased by at least a factor 20. Intravenous immunization, on the other hand, selectively expanded the Th cell population in the spleen, whereas the splenic Ts cell population and the Th and Ts cells in the lymph nodes were not affected. Comparison of these results with our previous data concerning characteristics and the requirements of in vivo activation of alloantigen-specific DTH reactive T cells and of alloantigen-specific Ts cells suggest that different Ts cell populations are involved in suppression of alloantigen-specific DTH in vivo and of allogeneic suppression of in vitro induced sheep erythrocytes specific antibody formation.     

Genetic and biological characterization of a T suppressor cell induced by anti-idiotypic antibody

The cellular and molecular characteristics of anti-idiotype-induced suppression have been investigated. We have shown that i.v. immunization of A/J or C.AL-20 mice with rabbit antibodies against the major cross-reactive idiotype on A/J anti-ABA antibodies induces splenic suppressor T cells (Ts) able to suppress T cell-mediated cytolytic and delayed-type hypersensitivity responses to ABA. In these studies, we compare the T suppressor activity manifested by anti-Id-induced suppressor cells with that described previously after conventional antigen priming. Results indicate that i.v. injection of anti-idiotypic antibodies primes for efferent level Ts; in contrast, i.v. administration of ABA-coupled cells induces afferent level suppressor cells. Soluble cell lysates, containing suppressor factor(s) derived from these anti-idiotype-induced Ts, can also mediate suppression of T cell immune responses in an efferent manner. Factor-mediated suppression is MHC-unrestricted and is also observed in mice pretreated with cyclophosphamide, suggesting that this activity is analogous to third-order suppression. Furthermore, this factor suppresses the T cell-mediated DTH and CTL responses in an antigen-nonspecific but Igh-restricted manner. These latter results suggest that the cellular elements conferring antigen specificity and Igh restriction are separate. The implications of these findings to the relationship between idiotypic elements, antigen-binding structures, and Igh restriction elements on immunoregulatory T cells are discussed.     

Characterization of the suppressor cell(s) responsible for anterior chamber-associated immune deviation (ACAID) induced in BALB/c mice by P815 cells

Anterior chamber-associated immune deviation (ACAID) is a complex set of immune responses induced by the inoculation of antigens into the anterior chamber of the eye. Histocompatibility antigens, tumor-specific antigens, reactive haptens, and viral antigens have been shown to induce this phenomenon, which comprises the following specific host responses: high titer humoral antibodies, primed cytotoxic T cells, but specifically, impaired skin graft rejection and delayed-type hypersensitivity (DTH). Using the model system of ACAID induced by inoculation of P815 mastocytoma cells into the anterior chambers of H-2-compatible, but minor H-incompatible, BALB/c mice, we demonstrate that the impaired capacity of these animals to develop and express DTH is due to the activation of suppressor T cells. Generation of these cells requires an intact spleen, is not inhibited by cyclophosphamide pretreatment, and is abrogated by systemic treatment of the host with anti-I-J monoclonal antibodies. This splenic suppressor cell(s) can transfer suppression of DTH adoptively to naive syngeneic mice. One suppressor cell is Thy-1.2, Lyt-2.2, and I-Jd positive. A minority of these cells (or a second population of suppressor cells) also expresses the L3T4 surface marker. Suppression is exerted on the efferent limb of DTH expression, although afferent suppression is not excluded. P815-induced ACAID suppressor cells resemble similar cells induced by haptenated spleen cells inoculated into the anterior chamber of the eye. We propose that induction of these suppressor cells, whose target of action is selective for T DTH cells, but not for other types of T cells, is responsible for the phenomenon of immune privilege in the anterior chamber of the eye.     

Dextran augments delayed-type hypersensitivity by interrupting one limb of the suppressor cascade

We have studied the immunomodulatory effect of dextran on the development of delayed-type contact hypersensitivity to a hapten in mice. Administration of an optimal dose of dextran 2 hours before applying picryl chloride to abdominal skin caused a twofold rise in the level of hapten-specific DTH. A study of the kinetics of development of DTH under the influence of dextran showed that comparable levels of response could be seen 2 days earlier in treated than in untreated mice, i.e., on the third day in contrast to the fifth day after sensitization. The peak of the responses, while greater in dextran-treated mice than in normal controls, remained the same at 5 days. Adoptive transfer studies revealed that comparable levels of DTH were conferred upon recipient mice by half the number of splenic cells from dextran-treated mice than that required from normal sensitized mice. Because several suppressor mechanisms are known to down-regulate DTH, we have studied dextran's effect on the neutralization of these systems as a possible explanation for its enhancing capabilities. Detailed examination was made of dextran's effect on the two suppressor T cells, Ts1 and Ts3, that act in tandem as well as its effect on the Ts1 and macrophage that work in combination. Both systems depress the efferent limb of DTH. We have found that dextran blocks the Ts1-macrophage pathway that controls DTH. Ts1 was found to arise normally in mice pretreated with dextran. Furthermore, Ts1 from dextran-treated mice produced TsF1 normally. However, we have found that dextran interferes with the production of macrophage suppressor factor (M phi-SF). Interference was partial when dextran was introduced during the interval in which macrophages were being armed with TsF1, and it was complete when dextran was put with pre-armed macrophages before they were triggered with antigen for production of M phi-SF. On the other hand, the Ts1-Ts3 limb of suppression remained unaffected by exposure to the immunomodulator. We found Ts3 arose normally in hapten-sensitized mice that had been pretreated with dextran. In addition, Ts3 became armed with TsF1 in vitro in the presence of dextran since the cells functioned properly to suppress mature DTH effector cells. Finally, TsF3 was able to act in vitro upon DTH effector cells despite the presence of dextran.(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunoregulation of lysozyme-specific suppression. III. Epitope-specific amplification of immunosuppression induced by monoclonal suppressor-T-cell products

The hen egg-white lysozyme (HEL)-specific suppression induced by soluble molecules produced by a monoclonal T-cell lymphoma line (LH8-105) obtained from HEL-specific suppressor T lymphocytes has been examined. Injection of I-J+ molecules from LH8-105 cell culture supernatant (TsFa) in HEL-primed mice during the afferent phase of the response induced Lyt-2+ second order suppressor T (Ts) cells which, upon transfer into HEL-CFA-primed syngeneic recipients, inhibit the delayed-type hypersensitivity (DTH) response to HEL. Transfer of spleen cells from TsFa-injected mice primed with HEL or human lysozyme suppresses the DTH response to HEL in recipient mice whereas this response is not affected by cell transfer from ring-necked pheasant egg-white lysozyme (REL)-primed and TsFa-injected mice, indicating that induction of second order Ts by TsFa is specific for a lysozyme epitope including phenylalanine at position 3. Fine antigenic specificity of second order Ts-cell induction is confirmed by similar results obtained upon injection of TsFa in mice primed with HEL N-terminal synthetic peptide or with an analog in which, as in REL, phenylalanine has been substituted by tyrosine at position 3. The same fine antigenic specificity observed in the induction of second order Ts cells is also present in the expression of TsFe suppressive activity. The similar antigenic specificity of Tsa and Tse suggests that Tse cells could result from amplification of the Tsa cell population or these two cell subsets could reflect different maturation stages of the same cell type rather than distinct T-cell populations activated in cascade.     

Functional analysis of cloned macrophage hybridomas. VI. Differential ability to induce immunity or suppression

We previously screened a series of macrophage hybridomas derived from fusion of P388D1 (H-2d) tumor cells with CKB (H-2k) splenic adherent cells for their ability to induce I-J restricted Ts cell responses. One Ia+ macrophage clone (63) consistently induced Ag-specific, I-J-restricted Ts. To evaluate whether macrophage hybridoma 63 also induced delayed-type hypersensitivity (DTH) immunity, mice were immunized with hapten-coupled macrophage hybridoma cells. Hapten-coupled splenic adherent cells and control macrophage hybridomas induced significant primary DTH responses, whereas hapten-coupled macrophage 63 induced little or no immunity when injected into H-2 compatible hosts. However, macrophage hybridoma 63 specifically activated I-Ak, I-Ad, or I-Ed restricted T cell hybridomas/clones, in vitro in the presence of appropriate Ag. Three different strategies designed to eliminate suppressor cell activity were successfully used to demonstrate that hapten-coupled macrophage 63 could also induce in vivo immunity. First, after immunization with hapten-coupled macrophages, mice were treated with cyclophosphamide. Second, macrophage 63 was treated with anti-IJ idiotype antibody before 4-hydroxy-3-nitrophenyl acetyl hapten (NP) coupling. Finally, haptenated macrophages were injected into I-A compatible but I-J incompatible recipients. These protocols are known to inhibit the induction of Ts activity, thus these results indirectly suggest that there is stimultaneous generation of Ts activity in vivo. The latter hypothesis was tested in adoptive transfer experiments. Transfer of lymph node cells from NP-63 primed B10.BR (H-2k) mice induced immunity in naive 4R animals, whereas the same number of immune cells suppressed NP-induced DTH responses in 5R mice. The combined results indicate that a cloned macrophage line can activate both Th and Ts cells. Macrophages which induce Ts activity may be responsible for maintaining the balance of immunity vs suppression. The data support the hypothesis that IJ interacting molecules (IJ-IM) expressed on macrophages are critical for induction of suppressor cell activity.     

Prevention of granuloma development in the mouse by using T cell hybridoma products

The ability of an azobenzenearsonate (ABA)-specific suppressor T cell factor, a soluble extract from first order suppressor T cells (Ts1), and suppressor molecules produced by a long-term T cell hybridoma to regulate ABA-specific granuloma formation was studied. ABA-derivatized syngeneic spleen cells (ABA-SC) administered subcutaneously induced persistent delayed-type hypersensitivity (DTH) responses, detected by footpad swelling and hapten-specific granuloma formation by 72 and 96 hr after challenge with ABA-bovine serum albumin coupled to polyacrylamide beads (ABA-BSA-PAB). Soluble factors from ABA-specific Ts1 prevented DTH and granulomatous development after subcutaneous administration of ABA-SC. Moreover, the in vivo administration of a factor that is derived from a Ts1 functioning hybrid cell line induced a second set of suppressor cells (Ts2) that upon transfer to syngeneic ABA-primed mice were able to inhibit granuloma formation in the footpad, as well as in the gastrointestinal tract after challenge with ABA-BSA-PAB. These experiments demonstrate the dependence of the granulomatous reaction on T cell-mediated events, as well as the potential therapeutic efficacy of an antigen-specific suppressor T cell factor and a hybridoma T cell product in limiting antigen-specific granuloma formation in vivo.     

Hapten-specific responses to the phenyltrimethylamino hapten. IV. Occurrence of mechanistically distinct idiotypic suppressor T cells before the appearance of anti-idiotypic suppressor T cells induced by the monovalent antigen L-tyrosine-p-azophenyltrimethylammonium

We have previously shown that a single i.p. injection of the monovalent synthetic antigen, L-tyrosine-p-azophenyltrimethylammonium [tyr(TMA)] in complete Freund's adjuvant induces an anti-idiotypic T suppressor cell (Ts2) population that can be detected 6 wk later by its ability to shut down delayed-type hypersensitivity (DTH) specific for the TMA hapten. In this paper we present evidence that 2 wk after tyr(TMA) administration, a subset of Ts, termed Ts1, appears that is both functionally and phenotypically distinct from the late appearing Ts2 population. The early occurring Ts1 act only at the induction phase of the DTH response and can also suppress this response intrinsically. This latter point is in marked contrast to our previous observation that the tyr(TMA)-induced anti-idiotypic Ts2 fail to function intrinsically and can only be detected upon adoptive transfer into naive mice. Ts1 bear idiotypic receptors and are Ly-1+,2- in contrast to the anti-idiotypic Ly-1-,2+ Ts2 population. In addition, unlike the Ts2 population, Ts1 are comparatively nylon wool-adherent. Adsorption of Ts1 on either antigen- or idiotype-coated petri dishes indicate that the suppressor activity can be transferred only by antigen-binding cells. Cellfree factors prepared from spleens containing the Ts1 population can suppress DTH only if administered at the induction phase of the response, in contrast to the factors derived from the Ts2 population that act both at induction as well as effector phases, suggesting that Ts1 and Ts2 can function via soluble mediators. Finally, we show that when Ts1-bearing mice are primed and boosted for anti-TMA antibody formation, the resulting response was overall reduced with respect to the idiotype-positive and negative plaque-forming cells that differs from the Ts2-bearing hosts wherein the idiotypic component is preferentially suppressed. The appearance of Ts1 before the detection of Ts2 in the same experimental animals is discussed with reference to a normal physiologic sequence of events involved in suppressor pathways.     

Induction of suppressor cells by a tumor-derived suppressor factor

Murine fibrosarcomas produce a factor that activates suppressor cells to inhibit expression of delayed-type hypersensitivity (DTH) responses to dinitrochlorobenzene (DNCB). This tumor-derived suppressor factor (TDSF) was partially purified by preparative isoelectric focusing of spent medium and 3 M KCl extracts of cultured methylcholanthrene-induced and spontaneous fibrosarcomas of C3H/He mice. Incubation of 1 micrograms/ml of a fraction, isoelectric pH less than 2.9, with normal syngeneic spleen cells for 1-6 hr at 37 degrees C induced suppressor cells that inhibited the primary DTH response to DNCB upon intraperitoneal transfer to normal C3H/HeJ mice. TDSF was not present in extracts of either syngeneic embryonic fibroblasts or normal spleen cells or in medium conditioned by normal peritoneal exudate cells but was present in 3 M KCl extracts of and the spent medium from four different cultured murine fibrosarcomas. TDSF activity was not restricted at the major histocompatibility complex. The suppressor cells inhibited the efferent limb of the DTH response because (1) hyporesponsive recipients of TDSF-treated spleen cells had splenic effector T cells capable of transferring DTH to DNCB into naive secondary recipients and (2) the ability of Lyt 1+,2- effector Tdth cells to transfer a secondary DTH response to DNCB was inhibited by co-incubation with macrophages or Lyt 1-,2+ T cells treated with TDSF. Preliminary biochemical analysis suggested that TDSF was an RNA- protein complex. Thus, several murine fibrosarcomas produced a soluble factor that activated splenic suppressor cells to depress the immune response to nonneoplastic antigens. These suppressor factors represent a novel group of regulatory molecules which may be ribonucleoprotein complexes.     

Evidence for a subpopulation of antigen-presenting cells specific for the induction of the delayed-type hypersensitivity response

Young adult SJL mice (8 weeks of age or younger) do not mount a delayed-type hypersensitivity (DTH) response due to the failure of a macrophage antigen-presenting cell (APC) to induce TDTH effector cells. SJL mice that are 10 weeks of age or older produce a normal DTH response. This genetic defect provides a model for the investigation of functional subpopulations of APC which interact with specific subpopulations of T cells. In this study, we used this model to examine whether macrophage APC impairment involves APC-dependent immune responses other than DTH. No age-dependent differences were found in the ability of spleen cells from SJL mice to proliferate and synthesize interleukin-2 in response to concanavalin A; nor was the proliferative response to a variety of antigenic stimuli affected. In addition, no differences were observed in the contact sensitivity response or in the in vitro generation of allogeneic cytotoxic T lymphocytes (CTL). In contrast, the in vivo generation of allogeneic CTL was significantly depressed in 6-week-old SJL and could not be restored to normal by the adoptive transfer of macrophages from DTH responsive 12-week-old SJL mice. Finally, examination of the humoral response of 6-week-old SJL indicated no impairment in IgM or IgG serum antibody levels or in the induction of splenic B cells. Thus, the macrophage APC regulating the induction of TDTH effector cells does not appear to participate in the induction of T helper cells for other cellular and humoral responses. These data support the hypothesis that distinct subpopulations of APC may regulate the induction of specific immune effector mechanisms.     

Suppressor T cell recognition of major and minor histocompatibility alloantigens: selected suppression of MHC-directed responses by minor alloantigen Ts

The induction of suppression by i.v. administered alloantigens in the murine host was analyzed as a model of the possible effects of blood transfusion on transplant survival. The results indicated that suppressor T cells (Ts) specific for minor histocompatibility alloantigens could be readily induced by the i.v. presentation of minor alloantigen-disparate spleen cells. In contrast, similar priming with cells differing solely at the H-2 major histocompatibility complex stimulated only positive T cell immunity, with no evidence of suppression. The induction of H-2 directed Ts activity could be accomplished only by i.v. priming with major plus minor incompatible donor cells, suggesting that suppressor cell recognition of minor alloantigens may have facilitated the generation of Ts against H-2-encoded major transplantation antigens. A role for minor histocompatibility antigens in the regulation of H-2-specific immunity at the effector level was also indicated. Ts induced by i.v. pretreatment with minor antigen-disparate donor cells not only suppressed the delayed-type hypersensitivity (DTH) response to the relevant minor alloantigens, but also inhibited DTH against unrelated H-2 alloantigens introduced during subsequent intradermal immunization. Suppression of H-2-directed T cell reactivity was specific in that the presence of the Ts-inducing minor alloantigens was also required and occurred only when the minor and unrelated major alloantigens were presented within the same inoculum, if not on the same cell surface. The capacity of Lyt-2+Ts or Ts-derived suppressive factors specific for one set of cell surface molecules to modulate responses to an unrelated group of surface antigens does not appear to represent a general phenomenon, because similar suppression of immunity to unrelated tumor-specific transplantation antigens by minor-specific Ts was not observed. These results are discussed with respect to the possible mechanism of H-2-directed suppression and the role of the I region in Ts recognition of antigen.     

A novel suppressive activity: complementation between a T cell induced with first-order T-suppressor factor and an I-J-restricted antigen-nonspecific T cell

Previous studies demonstrated that the first-order T-suppressor factor (TsF1) requires the presence of antigen to induce idiotype-specific Ts cells which readily suppress phenyltrimethylamino (TMA) hapten-specific delayed-type hypersensitivity (DTH) responses when transferred into already immune recipients. In this study we show that TsF1 in the absence of antigen induces a splenic population which limits DTH in recipient mice only when an additional accessory lymphoid population was also cotransferred. Neither of these populations alone was sufficient to mediate suppression and depletion of T cells in either population's abrogated suppression, indicating the T-cell dependency of the complementing cell types. Moreover, suppression was seen only when TMA-TsF1-induced and not normal spleen cell lysate-induced cells were cotransferred with the antigen-induced population, suggesting the requirement for a specific signal to induce the factor-induced population. Further experiments showed that the antigen-induced lymphoid population could be replaced by either heterologous antigen-induced or adjuvant alone-induced splenic populations, indicating the lack of specificity of this secondary population. Further analysis showed that the cell complementation between TMA-TsF1-induced and the nonspecific accessory lymphoid population resulted in antigen-specific and genetically restricted immune suppression. The TsF1-induced lymphoid population was not responsible for the genetic restriction, and furthermore, there was no restriction observed between the two complementing populations. However, matching of the nonspecific accessory cell with the recipient host at the I-J subregion of the H-2 complex was essential for immune suppression. Finally, the activity of complementing cells was found to be independent of cyclophosphamide-sensitive Ts populations of the recipient mice. The ramifications of these findings with reference to the existing suppressor pathways are discussed.     

Distinct populations of antigen-presenting cells are required for activation of suppressor and contrasuppressor T cells by type III pneumococcal polysaccharide

Type III pneumococcal polysaccharide (S3) coupled to spleen cells (S3-SC) has been shown to activate S3-specific Ts and Tcs in mice. Ts activation required I-J identity between carrier SC and Ts donors whereas I-A identity was required for Tcs activation. The carrier SC therefore presumably function as APC for Ts and Tcs activation by S3 since they are apparently not represented by APC present in the Ts and Tcs donors. The properties of the APC required for activation of S3-specific Ts and Tcs were determined by coupling S3 to various spleen cell subpopulations and assessing the ability of the various S3-SC populations to activate Ts and Tcs. The results indicate that Ts and Tcs are preferentially activated when S3 is presented on distinct cell types. S3-specific Ts were activated when S3 was coupled to plastic adherent cells. These cells are nonadherent to anti-Ig and nonfunctional in cyclophosphamide (Cy)-treated mice and their function is eliminated following treatment of cells with either anti-I-A or anti-I-J and C. In contrast, S3-specific Tcs were activated when S3 was coupled to anti-Ig adherent SC which bear I-A and the B cell marker J11d. These cells are functional in Cy-treated mice and their function is resistant to treatment with anti-I-J and C. Thus presentation of S3 on distinct cell types results in the preferential activation of T cells having opposing immunoregulatory function.     

Regulation of transplantation immunity in vivo by monoclonal antibodies recognizing host class II restriction elements. II. Effects of anti-Ia immunotherapy on host T cell responses to graft alloantigens

Results of the preceding report demonstrated that in vivo treatment with monoclonal anti-I-A antibodies provided an effective means of prolonging the survival of murine tail skin allografts. The mechanism of antibody action was shown to include the activation of alloantigen-specific suppressor T cells (Ts), although the relationship between Ts expression and graft survival was not determined. This issue was addressed in the current studies through a kinetic analysis of suppressor and effector T cell responses in control and treated allograft recipients. Donor-specific delayed-type hypersensitivity (DTH) and cytotoxic T lymphocyte (CTL) responses were detectable in untreated A/J recipients of B10.A allografts 8 days after transplantation, rising to near maximum levels by day 12. Rejection in these animals occurred by day 11. In contrast, the predominant cellular response of anti-I-A treated animals for 12 days after transplantation was that of transferable suppression, DTH and CTL reactivity not being evident until day 15, coincident with the decay of Ts activity. Rejection in these animals was observed approximately 19 days post-transplant. CTL responsiveness in the latter group could not be reconstituted by the addition of antigen-presenting cells to the secondary in vitro culture system, nor was the CTL deficit due to antibody carry-over. It is considered that the altered expression of effector cell responses to graft alloantigens is due at least in part to the in vivo inhibition of helper T cell activity by anti-I-A-induced Ts, and that rejection in the treated host results from an eventual decline in the functional expression of this regulatory T cell subset.     

Differential influence of 2'-deoxyguanosine on the induction and expression of suppressor T lymphocytes in vivo

Subcutaneous (sc) immunization of mice with allogeneic spleen cells can induce delayed-type hypersensitivity (DTH) to histocompatibility antigens. Intravenous immunization with irradiated allogeneic spleen cells, on the other hand, induces suppressor T (Ts) lymphocytes. These Ts cells are capable of suppressing the host-versus-graft (HvG) DTH reactivity which normally arises after sc immunization. Moreover they can suppress the development of antihost DTH effector T cells during graft-versus-host (GvH) reactions. These models for HvG and GvH DTH reactivity were used to study the influence of 2'-deoxyguanosine (dGuo) on the induction, further development, and expression of Ts cells in vivo. It was found that administration of dGuo inhibits the proliferation-dependent induction and further development of Ts cells, but not the suppression mediated by already activated Ts cells.