Ultraviolet-induced suppressor T cells and factor(s) in murine contact photosensitivity. III. Mode of action of T-cell-suppressor factor(s) and interaction with cytokines

The mode of action of T-cell-suppressor factor (TsF) induced by ultraviolet B (UVB) preirradiation in terms of interaction with several cytokines was studied. Suppression of murine contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) by preirradiation of the sensitizing site to low doses of UVB was caused by antigen-specific suppressor T cells (Ts) and was not associated with the generation of efferent limb-acting suppressor cells. TsF released by Ts inhibited the proliferation of immune lymph node (LN) cells in vitro and reduced interleukin (IL)-2 production of these cells in an antigen-specific fashion without affecting the IL-2 receptor (IL-2R) expression. Both rIL-2 and rGM-CSF have the ability to restore CPS responses in the UVB-preirradiated mice when administered after but not before photosensitization. However, rIL-2 but not rGM-CSF counteracted the in vivo inhibitory effect of TsF. rGM-CSF did not affect the density of I-A+ epidermal Langerhans cells (LCs). It was suggested that TsF inhibited IL-2-mediated immune T-cell proliferation, while rGM-CSF reconstituted the CPS by enhancing the function of photodamaged LCs. These results indicate multiple steps of the UVB-induced immunosuppression circuit, each of which seems to be controlled by different immunomodulators.     

Suppressor T cell circuits in contact sensitivity. III. A monoclonal T cell hybrid-derived suppressor factor specifically suppresses local DTH transfer by a DNP-specific T cell clone

Herein we described the direct suppressive effects of a monoclonal T cell hybridoma-derived, DNP-specific suppressor T cell factor (26.10.2 TsF) on the local transfer of delayed-type hypersensitivity (DTH) by a DNP-specific BALB/c T cell clone (dD1.9). The L3T4+, Lyt-2- dD1.9 T cell clone proliferated in response to DNP-OVA and DNBS, but not TNP-OVA or TNBS, in association with I-Ed determinants present on antigen-presenting cells. Similarly, local injection of histopaque-purified dD1.9 cell blasts resulted in DNP-specific, radioresistant, I-Ed-restricted, mononuclear cell-rich ear swelling responses. Incubation in 26.10.2 TsF specifically suppressed local transfer of DNP-specific DTH by dD1.9, but not local DTH responses transferred by BALB/c T cell clones specific for TNP or GAT. The suppressive effect of 26.10.2 TsF correlated with targeting on DNP-major histocompatibility complex determinants associated with the DTH T cell (TDH) targets. 26.10.2 TsF-mediated suppression was most pronounced after exposure of dD1.9 target cells to antigen (after the stimulation phase of the T cell clone maintenance procedure), and greatly reduced when dD1.9 was cultured for long periods in the absence of DNP (after the rest phase of clone maintenance). In additional support of this hypothesis, GAT-specific TDH, normally resistant to 26.10.2 TsF-mediated suppression, were rendered susceptible to suppression after surface DNPylation. The results demonstrate a direct, antigen-specific, effector phase regulatory effect of a monoclonal TsF on a cloned, antigen-specific T cell target, and strongly suggest that suppression is mediated via targeting on DNP determinants associated with the TDH target. Simplification of complex Ts circuitry operating in suppression of the efferent limb of DTH by the use of monoclonal TsF and cloned T cell targets should provide a basis for the future study of the molecular mechanisms of immune suppression.     

Antigen-specific suppressor T cell interactions. I. Induction of an MHC-restricted suppressor factor specific for L-glutamic acid50-L-tyrosine50

The synthetic polymers L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT) and L-glutamic acid50-L-tyrosine50 (GT) stimulate specific suppressor T cells in certain strains of mice. Extracts from these T cells contain factors (TsF) that inhibit GAT- or GT-specific antibody responses by normal spleen cells or proliferative responses by primed T cells. We constructed T cell hybridomas that constitutively produce GAT-TsF or GT-TsF, which functionally and serologically are identical to factors extracted from suppressor T cells. In this report we demonstrate that monoclonal GT-TsF can induce specific unresponsiveness in vivo or in vitro and that this unresponsiveness is due to development of second-order antigen-specific suppressor T cells. T cell hybridomas were constructed by fusion of BW5147 with GT-TsF1 induced second-order suppressor T cells and clones that produced suppressor factor (GT-TsF2) were isolated and characterized. GT-TsF2 differs from the GT-TsF1 used to induce it in that GT-TsF1 acts across allogeneic barriers whereas GT-TsF2 does not. This restriction is controlled by genes in the H-2 gene complex and maps to the I-J subregion. GT-TsF2 is antigen-specific in suppressive activity and also in its antigen-binding site(s). Thus, GT-TsF2 closely resembles the carrier-specific, I-J+, genetically restricted factor described by Tada and his colleagues. Because GT-TsF2 was induced by GT-TsF1, we suggest cells producing GT-TsF1 are an early cell in the pathway of suppression, and that this cell is required for the activation of antigen-specific, MHC-restricted TsF.     

Suppressor T cell circuits in contact sensitivity. II. Induction and characterization of an efferent-acting, antigen-specific, H-2-restricted, monoclonal T cell hybrid-derived suppressor factor specific for DNFB contact hypersensitivity

This report defines a methodology for the production and characterization of an antigen-specific, monoclonal T cell hybrid-derived suppressor T cell factor (TsF) that suppresses the passive transfer of 2,4-dinitrofluorobenzene (DNFB) contact hypersensitivity. Fusion of T cells from BALB/c (H-2d) mice tolerized with syngeneic DNP-spleen cells to BW 5147 thymoma cells resulted in several hybrids that constitutively produce a soluble regulatory molecule. One of these hybrids, 26.10.2, was subsequently cloned, and its soluble factor was characterized with respect to its antigen specificity, biochemical nature, MHC restriction pattern, and identity of its target cell. 26.10.2 TsF suppresses the passive transfer of delayed-type hypersensitivity (DTH) mediated by DNP- but not trinitrochlorobenzene- or oxazalone-primed DTH T cells (TDH) after a 1 hr incubation at 37 degrees C. In contrast, 26.10.2 TsF had no suppressive effect on secondary in vitro DNP-specific T cell proliferative responses. 26.10.2 TsF therefore represents an antigen-specific factor with effector (efferent-acting) function. The monoclonal TsF was shown to consist of a two-chain, disulfide-bonded molecule, and to bear a receptor(s) specific for DNP and determinants encoded by the I region of the H-2 complex. Effector suppressive activity of 26.10.2 TsF was restricted by Class I H-2Dd determinants. One cellular target of this monoclonal factor was shown to be the DNP-specific TDH cell, because DNFB-primed lymph node cells from cyclophosphamide-pretreated donors (lacking Ts-auxiliary (Ts-aux) cells) were efficiently suppressed. The TsF appears to focus on passively bound, TDH receptor-associated, DNP-Class I determinants, as suggested by the observation that freshly prepared, but not overnight cultured, DNP-specific TDH cells were susceptible to suppression.     

Mechanisms of contact photosensitivity in mice. IV. Antigen-specific suppressor T cells induced by preirradiation of photosensitizing site to UVB

Mice were successfully contact photosensitized with 3,3',4',5-tetrachlorosalicylanilide (TCSA) plus black light irradiation. Pre-exposure of the photosensitizing site (ca 5 cm2) to UVB (280 to 320 nm; 400 mJ/cm2) rendered mice unresponsive to a challenge reaction. Cell transfer experiments demonstrated that the spleens from the nonreactive mice contained suppressor T cells (Ts) that were antigen-specific and that blocked the afferent limb of contact photosensitivity to TCSA. To exert suppressive functions, Ts required another population of cyclophosphamide-sensitive T cells that resided in the spleens of nonsensitized mice. The results provide evidence that UVB-induced aberrant homeostasis of the skin caused a marked suppression of immune system that is associated with the generation of Ts.     

Reconstitution of an inactive antigen-specific T cell suppressor factor by incubation of the factor with prostaglandins

Experiments were performed to test the hypothesis that prostaglandins are crucial to the ability of an antigen-specific T cell suppressor factor to deliver a suppressive signal. In the system employed, T suppressor cells release an antigen-specific factor (TsF) that suppresses the ability of effector cells to transfer contact sensitivity (CS) skin swelling responsiveness to adoptive recipients. Culture of TsF-producing cells in the presence of indomethacin caused production of an inactive TsF that could be reconstituted by incubation of this inactive factor with low concentrations of certain prostaglandins such as PGE2 or PGE1. Subsequently, nearly all the prostaglandins were removed by dialysis, and the reconstituted TsF then acted as an antigen-specific suppressor of CS effector cells. Neither the inactive factor nor prostaglandins were suppressive alone. Furthermore, the prostaglandins are crucial to the constitution of TNBSA-F, the non-antigen-binding subunit of the TsF that probably delivers the ultimate suppressive signal. These results provide a new type of antigen-specific role for prostaglandins in immunoregulation and indicate that simple, local, hormonal molecules in physiologic concentrations can have a crucial and long-lasting role in constituting the suppressive activity of antigen-specific regulatory macromolecules released by suppressor T cells.     

Antigen-specific human T cell factors. II. T cell suppressor factor: biologic properties

The in vitro induction of an ovalbumin-specific human T cell suppressor factor is described (TsF120-OA). The antigen-specific suppressive component can be purified by affinity chromatography from supernatants derived from Marbrook-Diener type cultures of peripheral blood T cells stimulated with a high dose of ovalbumin. TsF120-OA suppresses the antigen-induced PFC formation of human blood B cells in vitro in an antigen-specific way. The target of TsF120-OA activity is shown to be the T helper cell. No genetic restriction in the action of the factor is observed.     

Suppression and contrasuppression in athymic nude mice: nude mice produce the antigen-specific component of a T suppressor factor that inhibits the late 24-hr phase of DTH but do not generate suppression nor contrasuppression of the early initiating phase of DTH.

Previous studies demonstrated that the initiation of murine delayed-type hypersensitivity (DTH), as exemplified by contact sensitivity induced by picryl chloride (PCI) or oxazolone (OX), is due to antigen-specific, T cell-derived, DTH-initiating factors called, respectively, PCl-F and OX-F. These factors participate in the extravascular recruitment of CD4+, Th-1, DTH effector T cells in the elicitation of DTH. Related factors also participate, together with nonantigen binding factors derived from CD8+ T cells, to constitute an antigen-specific T cell-derived suppressor factor (TsF) that can down regulate the ability of Th-1 effector T cells to mediate DTH. Since it was shown recently that athymic nude mice can make antigen-specific, DTH-initiating T cell factors, the current study tested whether nude mice also could produce the antigen-specific component of the TsF that suppresses DTH effector T cells. We found that antigen-specific factors from nu/nu mice could complement the nonantigen-binding subfactor produced in normal mice to constitute the whole antigen-specific TsF. Additional studies showed that the successful adoptive cell transfer of DTH-initiating T cell activity from nude mice into normal mice required cyclophosphamide treatment of the recipient. In contrast, transfer of DTH-initiating cell activity from nu/+ mice did not require cyclophosphamide treatment of the recipients. We hypothesized that nude mice lacked contrasuppressor cells. Although nude mice were able to manifest the early, initiating phase of DTH, we found that there was no suppression of early DTH-initiating T cells in nude mice, compared to nu/+. Therefore the production of DTH-initiating T cell factor could be boosted in nude mice. The ability to boost DTH-initiating cells in nude mice should facilitate the development of cell lines and clones with the ability to initiate DTH.     

Characterization of an antigen-specific suppressive factor derived from a cloned suppressor effector T cell line

A cloned effector-type suppressor T cell line, 3D10, which is known to suppress the antibody response against dinitrophenylated keyhole limpet hemocyanin (KLH), produced a soluble KLH-specific factor (TsF) that can replace the function of parental T cell clones. High activity of TsF was released spontaneously into the culture supernatant when cultured in interleukin 2 (IL 2)-containing medium, requiring no antigenic stimulation. The culture supernatant of 3D10 was also capable of inhibiting the KLH-induced proliferative response of primed T cells in an antigen-specific manner. The direct target of TsF was found to be Lyt-1+2- T cells undergoing an early stage of antigen-specific proliferation. TsF was antigen binding but lacked any other serologic markers such as I-J and immunoglobulin heavy chain-linked allotypic determinants on T cells. No genetic restriction was found in its action on allogeneic T cells. The production of IL 2 in proliferative T cells by antigenic stimulation was not inhibited by TsF. These results indicate that the TsF described here is the legitimate mediator produced by the effector-type suppressor T cell that suppresses the antigen-specific responses of Lyt-1+2- T cells. The m.w. of TsF was approximately 75,000.     

Downregulation of helper T cells by an antigen-specific monoclonal Ts factor.

The findings of previous studies in this laboratory demonstrating that conjugates of human monoclonal (myeloma) IgG (HIgG) and monomethoxypolyethylene glycol (mPEG) were able to induce in mice antigen-specific tolerance and CD8+ suppressor T (Ts) cells were confirmed in the present study. An extract (TsF) of a nonhybridized clone of Ts cells (viz., clone 23.32), which had been derived from spleen cells of mice tolerized with HIgG(mPEG)26, was shown to possess antigen-specific suppressive activity. This monoclonal TsF was able to specifically suppress in vitro antibody formation only if it was present from the beginning of the culture. From the results of the cellular dissection of the system used it was concluded that (i) the TsF had no effect on fully differentiated primed B cells or plasma cells, and (ii) the TsF inactivated carrier-primed Th cells when the culture contained concomitantly naive CD8+ T cells, accessory cells, and antigen. These data support the view that the monoclonal TsF exerted its downregulating effect on Th cells only if it could first interact with a CD8+ T cell, in the presence of accessory cells and antigen.     

Mechanism of action of a T suppressor factor (TsF) in contact sensitivity: the T cell target for TsF activity in adoptive transfer of immunity is not effector cell

The passive transfer of contact sensitivity (CS) by immune cells into normal animals requires the interaction of two distinct Ly-1+ T cells, one which is Vicia villosa lectin (VV)-nonadherent, the other which adheres to VV. Functional deletion of either cell type abrogates the adoptive transfer of CS into normal animals, whereas VV-nonadherent cells alone can transfer CS into animals pretreated with cyclophosphamide (Cy). An antigen-specific T suppressor factor, designated TNP-TsF, inhibits the transfer of CS into normal adoptive recipients. TNP-TsF mediates its suppressive activity by inducing an I-J+ subfactor (designated I-J2) from the assay population by the interaction of PC1-F (a TNP-binding subfactor of TNP-TsF) with antigen-primed Ly-2+ T cells. This I-J+ subfactor then complements TNBS-F (an antigen-nonbinding subfactor of TNP-TsF) to form an antigen-nonspecific effector molecule which suppresses DTH responses in an antigen-nonspecific fashion. We report here that TNP-TsF suppresses the adoptive transfer of CS into normal animals but not into animals pretreated with Cy. TNBS-F + I-J2, the effector complex of TNP-TsF, also suppresses the transfer of CS into normal but not Cy-treated animals. When the Ly-1 immune cells were separated into VV-adherent and -nonadherent populations, the TNBS-F + I-J2 suppressor complex suppressed the functional activity of the VV-adherent cell population, but not the VV-nonadherent cells. This suppressive activity correlates with the need for VV-adherent cells in the transfer of CS into normal but not Cy-treated recipients. When an I-J+ molecule (I-J1) from an SRBC-specific TsF was used in place of I-J2 to form a suppressor complex with TNBS-F, this TNBS-F + I-J1 TsF suppressed the transfer of CS into both normal and Cy-treated recipients. This difference in functional suppressive activity correlated with a difference in target cell specificity: TNBS-F + I-J1 suppressed the VV-nonadherent TDTH cell, whereas TNBS-F + I-J2 suppressed the VV-adherent T cell of CS. Immune cells which are transferred under conditions which do not require the VV-adherent cell for transfer are not suppressed by TNBS-F + I-J2 or TNP-TsF, but are suppressed by the TNBS-F + I-J1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antigen-specific T cell-mediated suppression. II. In vitro induction by I-J-coded L-glutamic acid50-L-tyrosine50 (GT)-specific T cell suppressor factor (GT-T8F) of suppressor T cells (T82) bearing distinct I-J determinants.

The induction of new suppressor T cells (Ts2) by suppressive extracts (TsF) from L-glutamic acid50L-tyrosine50 (GT) nonresponder mice was examined. Incubation of normal spleen cells with allogeneic GT-TsF for 2 days in vitro led to the generation of Ts2 cells able to suppress subsequent responses to the immunogen GT-methylated bovine serum albumin (GT-MBSA) in vivo. This induction occurred efficiently when TsF donor and target cells differed at all of H-2, including the I-J subregion. B10.BR (H-2k) GT-TsF, adsorbed on, then acid eluted from GT-Sepharose and anti-I-Jk [B10.A (3R) anti-B10.A (5R)]-Sepharose in a sequential fashion could induce BALB/c (H-2d) spleen cells to become Ts2 only if nanogram quantities of GT were added to the purified GT-TsF. This indicates a requirement for a molecule or molecular complex possessing both I-J determinants and antigen (GT)-binding specificity, together with GT itself, for Ts2 induction. The induced Ts2 are I-J+, since their function can be eliminated by treatment with anti-I-Jk plus C. These I-J determinants are coded for by the precursor of the Ts2 and do not represent passively adsorbed, I-J coded TsF, since anti-Ijk antiserum [(3R X DBA/2)F1 anti-5R] which cannot recognize the BALB/c (I-Jd) TsF used for induction still eliminates the activity of induced A/J (I-Jk) Ts2. These data provide further evidence for and information about the minimum of two T cells involved in antigen-specific suppressor T cell systems.     

Regulation of contact sensitivity reaction: contrasuppressor T cells and contrasuppressor factor downregulate efferent T suppressor cells.

Contact sensitivity (CS) reaction mediated by CD 4+8- Th 1 cells is under the control of several antigen-specific regulatory lymphocytes. Reaction is downregulated at the induction stage by T afferent suppressor T cells (Ts-aff) that prevent immunization and at the effector stage by efferent T suppressor cells (Ts-eff) that made immune Th 1 cells inoperative. Both suppressor cells are CD 4-8+ Th 1 effector cells and are protected against the suppressive action of Ts-eff cells by CD 4+8- contrasuppressor T cells (Tcs). As has been already shown there are also regulatory interactions between regulatory cells themselves and Ts-aff cells in addition to their effect on precursors of Th 1 cells, also preventing the induction of Ts-eff cells. The present experiments extend these findings and demonstrate that Ts-eff cells are also under negative control of Tcs lymphocytes. Likewise, antigen-specific factor produced by contrasuppressor T-T cell hybridoma, used in lieu of Tcs cells, impedes the activation of Ts-eff cells. In both cases regulation is aimed at the precursors of Ts-eff cells. Our experiments demonstrate that the outcome of immunization is dependent not only on the balance between immune cells and regulatory cells, but also on interactions between regulatory cells themselves.     

Hapten-specific responses to the phenyltrimethylamino hapten. V. A single chain antigen-binding I-J+ first-order T suppressor factor requires antigen to induce anti-idiotypic second-order suppressor T cells

We have previously shown that a single i.p. injection of the monovalent antigen, L-tyrosine-p-azophenyltrimethylammonium in complete Freund's adjuvant induces a Ly-1+2-, idiotype-bearing, and antigen-binding first-order T suppressor (Ts1) population. We showed that soluble factors extracted from these cells could suppress delayed-type hypersensitivity responses if administered at the induction phase of the response. In this paper we additionally characterize the suppressor factor, TsF1, with respect to its biologic, serologic, and chemical properties. The studies show that the TsF1 is neither allotype nor H-2 restricted and can induce anti-idiotypic T suppressor cells (Ts2), but it requires the presence of antigen to do so. The factor binds antigen, bears I-J encoded determinants, is resistant to reduction and alkylation, and elutes as a single chain factor after adsorption onto monoclonal anti-I-J antibody-coupled Sepharose beads in the presence of dithiothreitol (DTT). This is in marked contrast to TsF2 (derived from Id-specific Ts2-containing spleen cells), which lost its suppressive activity after reduction and alkylation, and behaves as a two chain factor after adsorption and elution from anti-I-J-coupled beads in the presence of DTT. The TsF1 is discussed with respect to the properties of it and those of TsF1 from other similar idiotype-dominated antigen systems.     

Nonspecific T suppressor factor (nsTsF) cascade in contact sensitivity: nsTsF-1 causes an Ly-1+2- I-A+ immune T cell to produce a second, genetically restricted, nsTsF-2

We studied the mode of action of the nonspecific T suppressor factor (nsTsF-1) made in the picryl (TNP) system when T acceptor cells armed with antigen-specific TsF are triggered by antigen in the context of I-J. This suppressor factor does not inhibit the passive transfer of contact sensitivity directly, as shown by its failure to inhibit passive transfer by immune cells deprived of I-A+ cells. Its immediate target is an immune, antigen-specific, Ly-1+2-, I-A+ T cell. This cell, which may be regarded as a T suppressor effector cell (Ts-eff-2), produces nsTsF-2 when exposed sequentially to nsTsF-1 and antigen. This nsTsF subsequently inhibits the passive transfer of contact sensitivity. The action of nsTsF-2 is MHC genetically restricted. As the nsTsF-2 bears I-A determinant(s), this raises the possibility that it may act by combining with the recognition site for I-A on the T cell that mediates contact sensitivity.     

T suppressor factor activity is due to two separate molecules. The Lyt-1(-)2+I-J+ cells of mice primed with antigen make an antigen binding molecule which is only active when complemented by cofactor made by Lyt-1+2(-)I-J+ cells

Mice primed with picrylsulfonic acid (PSA) and then painted on the skin with picryl chloride produce antigen-specific T suppressor factor (TsF). In contrast unpainted primed mice fail to produce active TsF. This is not due to the absence of the antigen binding part of TsF but to the absence of a cofactor. This cofactor is (a) antigen nonspecific and occurs in potassium chloride extract of normal spleen cells. It also occurs in the 24 hr supernatant of normal cells modified by haptenisation with picryl or the unrelated NP antigen (4-hydroxy-3-nitrophenylacetyl), and in preparations of conventional TsF (PSA/PCl) from painted PSA-primed mice; (b) bears I-J determinants; and (c) is produced by Lyt-1+2(-)I-J+ cells. The antigen binding molecule occurs alone in the supernatant of PSA-primed mice. It lacks I-J determinants and has a molecular weight around 35,000 and 75,000. It is produced by Lyt-1(-)2+I-J+ cells and is only active when complemented by cofactor. However, the complementation is genetically restricted and the restriction maps to the I-J subregion of the MHC.     

Cloned suppressor T cells derived from mice tolerized with conjugates of antigen and monomethoxypolyethylene glycol. Relationship between monoclonal T suppressor factor and the T cell receptor

Cloned Ts cells specific for the Ag, human monoclonal (myeloma) IgG, were derived from spleen cells of mice that had been immunosuppressed by treatment with a tolerogenic conjugate of HIgG and monomethoxypolyethylene glycol. The cloned Ts cells (clone 23.32) suppressed in vitro antibody responses in an Ag-specific and MHC-restricted manner. By FMF with appropriate antibody reagents, these cells were shown to be Thy-1+, CD4-, CD5-, and CD8+ and to express CD3 and the alpha beta-TCR. These results are consistent with the view that Ts cells use Ag recognition structures similar to those reported for Th cells and CTL. A soluble factor (TsF) extracted from the cloned Ts cells also suppressed in vitro antibody responses in an Ag-specific and H-2Kd-restricted manner, i.e., restricted to MHC class I molecules. The suppressive activity of this TsF could be abrogated by addition of mAb H28-710 that reacts with a determinant on the alpha-chain of TCR. Moreover, the TsF bound to and could be recovered from an immunosorbent consisting of the anti-alpha-TCR mAb H28-710 coupled to Sepharose 4B. In contrast, the TsF was not bound by immunosorbents consisting of mAb to the beta-chain of TCR (H57-597) or to V beta 8 (F23.1). It was, therefore, concluded that the TsF of clone 23.32 is serologically related to the alpha-chain of the TCR; however, it is not identical to TCR, because it lacks the determinants expressed on the TCR beta-chain that are recognized by the two anti-beta mAbs used in this study.     

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.     

Immunologic regulation of experimental cutaneous leishmaniasis. V. Characterization of effector and specific suppressor T cells

Resistant CBA mice infected with Leishmania tropica promastigotes develop concomitant and convalescent immunity against reinfection. This can be adoptively transferred by splenic and lymph node T cells with a threshold dosage of 1 to 2.5 x 10(7). The effector cells are of Thy-1+, Lyt-1+2- phenotype. The same immune cell population also adoptively transfers specific DTH to L. tropica, which is restricted by the major histocompatibility complex. On the other hand, highly susceptible BALB/c mice infected with L. tropica develop antigen-specific suppressor T (Ts) cells (previously shown to inhibit the induction and expression of DTH), which are capable, on transference, of reversing the healing of lesions induced by prior sublethal irradiation of BALB/c mice. As few as 10(6) of these T cells are effective in abrogating the potent prophylactic effect of 550 rad. The Ts cells are of Thy-1+, Lyt-1+2-, and I-J- phenotype. Sublethally irradiated and infected BALB/c mice produce antibody responses quantitatively and isotypically similar during the critical first 40 days after infection whether or not they are injected with 10(7) Ts cells (nonhealing vs healing). Thus, impairment of DTH and curative immune responses in BALB/c mice cannot be attributed to a helper function of these Thy-1+, Lyt-1+2- cells for the formation of suppressive antibody.     

Interaction of idiotype-specific T suppressor factor with the hapten-specific third-order T suppressor subset results in antigen-nonspecific suppression

The interaction between the third-order T suppressor (Ts3) cell and the idiotype (Id)-specific second-order Ts factor (TsF2) was studied in the phenyltrimethylamino (TMA) hapten system. The experimental system which we used allowed the independent analysis of induction and activation requirements of Ts3. The procedure consisted of inducing the Ts3 in vivo and activating the enriched T-cell populations containing Ts3 in vitro with TsF2. The suppressive potential was then tested in mice previously primed for delayed-type hypersensitivity responses which were also treated with cyclophosphamide to deplete Ts3 and other drug-sensitive Ts cell types. Using this experimental system, it was found that the Id-specific TsF2 was required for the in vitro activation of Ts3. Furthermore, the TsF2 activated only the homologous and not heterologous antigen-primed Ts3-containing T cells and moreover, the target of TsF2 was found to be the Ts cells bearing hapten-specific receptors. Once the TMA hapten-specific Ts3 was activated with TsF2, the ensuing suppression was antigen nonspecific. The data demonstrate that the Ts3 represents a final effector Ts cell type in the TMA system.