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.     

Differential responsiveness to MIs locus antigens in graft-versus-host and host-versus-graft reactions

After (semi)allogeneic transplantation of lymphoid cells into lethally irradiated mice, the development of anti-host directed T effector cells can be demonstrated by means of a simple delayed-type hypersensitivity (DTH) assay. Using this assay we have shown that in H-2 compatible combinations Mls locus antigens can induce the generation of such T effector cells during a graft-versus-host (GvH) reaction. Other non-H-2 alloantigens are probably of minor importance. The capacity of Mls locus antigens to induce distinct anti-host DTH reactivity correlated with the capacity to induce a one-way mixed lymphocyte culture (MLC) response. Mls^a and Mls^c locus antigens initiated a positive MLC response as well as distinct GvH-related DTH reactivity. On the other hand, in the combination DBA/2 versus (BALB/c × DBA/2) F₁, the Mls^b locus antigen was not able to initiate in vitro proliferation, a lack of response which coincided with a marginal and short-lasting GvH-related DTH reactivity. In contrast, the host-versus-graft (HvG) DTH reaction of BALB/c and DBA/2 mice to subcutaneously injected (BALB/c × DBA/2) F₁ spleen cells was equally strong. Here antigens other than those coded for by the Mls locus were mainly responsible for the antigraft DTH response. These results suggest that T effector cells generated in GvH and HvG reactions are specific for largely different sets of minor histocompatibility antigens, with a selective stimulation by Mls locus antigens under GvH conditions.     

Restricted recognition of H-2 subregion coded alloantigens in delayed-type hypersensitivity

Subcutaneous (sc) immunization of mice with H-2K, I, or D incompatible spleen cells induces a state of host-versus-graft (HvG) delayed-type hypersensitivity (DTH). The DTH reaction is elicited by challenging the immunized mice in a hind foot with similar allogeneic spleen cells and is measured as the subsequent foot swelling. DTH effector T cells specific for H-2I-coded alloantigens, but not for H-2K/D-coded alloantigens, can be induced in a graft-versus-host (GvH) model as well. In this paper we report that under HvG as well as under GvH conditions the recognition of class II antigens by DTH effector T cells is restricted by class I molecules. Furthermore, DTH effector T cells induced by sc immunization with class I antigens appear to be restricted by class II molecules.     

Synergism of T lymphocyte subsets in the response to Mls-locus coded antigens during graft-versus-host reaction

After transplantation of lymphoid cells into lethally irradiated (semi)allogeneic mice specific anti-host directed effector T cells are generated. This can be demonstrated using a delayed type hypersensitivity (DTH) assay. In H-2 compatible combinations, Mls-locus antigens, but no other minor histocompatibility antigens, can induce the generation of such effector T cells. This paper shows that maximal anti-host DTH responses are obtained when the lymphoid cells transplanted constitute of a mixture of long-lived, recirculating T2 cells and short-lived, sessile T1 cells. It was demonstrated that anti-Mls locus-directed DTH effector T cells are the progeny of T2 cells, and that T1 cells amplify this response. The latter, however, are by themselves incapable of displaying anti-Mls DTH reactivity. The T1 cells were found to be of the Lyt-1+2+ phenotype, and the T2 cells of the Lyt-1+2- phenotype. The same Lyt phenotypes were found for T1 and T2 cells synergizing in the GvH reaction against H-2 alloantigens.     

Generation of suppressor T cells after local immunization with histocompatibility antigens

Subcutaneous (sc) hind-foot immunization (HFI) of mice with allogeneic spleen cells can induce a state of delayed-type hypersensitivity (DTH) as well as a state of suppression of DTH. This paper deals with the suppression induced by HFI. The state of suppression could be adoptively transferred by spleen cells and lymph node cells between Days 3 and 7 after HFI only. However, in the hind-foot-immunized mice the state of suppression lasted at least 25 days. The suppressor cells expressed the Thy-1+, Lyt-1-2+ phenotype and suppressed DTH antigen-specifically. The suppressor cells, however, also suppressed DTH responses to unrelated third-party alloantigens, provided the latter were administered during the induction of DTH together with the same alloantigens that were used for HFI. The HFI-induced T-suppressor cells suppressed the induction phase of DTH (i.e., the proliferative activity of the draining lymph node cells after secondary sc immunization), but not the expression phase of DTH (i.e., the activity of previously activated DTH effector T cells). H-2D compatibility between the donors of the HFI-induced T-suppressor cells and the recipients was required for the adoptive transfer of suppression. The differences in effect of local immunization versus systemic immunization on the induction and functional activity of T-suppressor cells are discussed.     

Abrogation of the capacity of delayed-type hypersensitivity responses to alloantigens by intravenous injection of neuraminidase-treated allogeneic cells

BALB/c or C3H/He mice were inoculated i.v. with allogeneic spleen cells untreated or treated with neuraminidase. Appreciable or potent anti-allo-delayed-type hypersensitivity (DTH) responses were observed when mice were inoculated i.v. with untreated allogeneic cells or inoculated i.v. with those cells followed by s.c. immunization with untreated allogeneic cells. In contrast, i.v. inoculation of neuraminidase-treated allogeneic cells (presensitization) not only failed to induce any significant anti-allo-DTH responses but also abolished the capability of the animals to develop DTH responses after s.c. immunization, indicating the tolerance induction. This tolerance was alloantigen-specific, and rapidly inducible and long lasting. The induction of suppressor cell activity was demonstrated in tolerant mice. However, this activity was associated only with the tolerant state around 4 to 7 days after the i.v. presensitization, but was no longer detected in mice more than 14 days after the presensitization, although these mice exhibited complete tolerant state. When spleen cells from such tolerant mice were transferred i.v. into 600 R x-irradiated syngeneic recipient mice alone or together with normal syngeneic spleen cells, these tolerant spleen cells themselves failed to induce DTH responses but did not exhibit suppressive effect on the generation of DTH responses induced by normal spleen cells co-transferred. These results indicate that i.v. administration of neuraminidase-treated allogeneic cells results in the induction of alloantigen-specific tolerance which is not always associated with the induction of suppressor cell activity but rather with the elimination or functional impairment of alloantigen-specific clones.     

Delayed-type hypersensitivity (DTH) in BCG-sensitized mice I. Lack of suppressor T cell activity on DTH to sheep red blood cells.

Mice pretreated with an intravenous (i.v.) injection of BCG (BCG-sensitized mice) and then immunized intravenously with a high dose (10(8)--10(9)) of sheep red blood cells (SRBC) 2 weeks later developed strong delayed-type hypersensitivity (DTH) to SRBC, as in mice pretreated with cyclophosphamide (CY) (CY-treated mice) and then immunized with SRBC 2 days later; normal mice given the same dose of SRBC did not show such DTH. The mechanism of this strong DTH to SRBC which developed in BCG-sensitized mice was studied, by comparing it with that in CY-treated mice. The transfer of either whole spleen cells or thymus cells, but not serum, obtained from mice immunized with i.v. injections of 10(9) SRBC 4 days previously (hyperimmune mice) did not suppress either the induction or the expression of DTH to SRBC in BCG-sensitized mice, but suppressed those in CY-treated mice. The suppressor cells were SRBC-specific T cells. Adoptive transfer of DTH to SRBC by spleen cells from either BCG-sensitized mice of CY-treated mice to hyperimmune recipients failed. The adoptive transfer of DTH from BCG-sensitized mice to normal recipients also failed if the spleen cells from hyperimmune mice were cotransferred. Whole body irradiation (600 rad) of mice 2 hr before or after the time of immunization with SRBC reduced significantly DTH to SRBC in both BCG-sensitized and CY-treated mice. It was noticed that the total number of spleen cells in BCG-sensitized mice was 3--4 times larger than that in CY-treated mice. From these results, we conclude that the entity of effector T cells of DTH to SRBC induced in BCG-sensitized mice and in CY-treated mice was not different in terms of susceptibility to suppressor T cells and irradiation, but that the total numbers of effector T cells generated in these mice differed remarkably, resulting in the above-described different responsiveness to suppressor T cells transferred passively.     

Suppression of delayed-type hypersensitivity to syngeneic testicular cells in mice: involvement of suppressor T cells which act at the induction stage

Suppressor cells for delayed footpad reaction (DFR) against syngeneic testicular cells (TC) were detected in the spleen cells of donor mice immunized intravenously (iv) with viable syngeneic TC. Cyclophosphamide (CY)-pretreated recipients were given spleen cells from donors iv, immunized subcutaneously (sc) with syngeneic TC, and the footpad reaction at 24 hr was elicited with syngeneic TC 6 days after immunization. DFR in the recipients was suppressed by the transfer of spleen suppressor cells. The suppressor cells induced were Thy-1+, CY-sensitive, adult thymectomy (ATx)-resistant and act only at the induction stage. They directly suppress the generation of effector T cells for delayed-type hypersensitivity (DTH). When mice pretreated with CY were actively immunized with syngeneic TC, DFR could be provoked to a measurable level only when they were immunized sc. However, peritoneal exudate cells of those tolerant mice immunized sc without CY pretreatment or immunized iv with CY pretreatment also passively transferred DFR locally, suggesting the existence of effector T cells for DTH even in tolerant mice.     

Suppression of delayed-type hypersensitivity to third party "bystander" alloantigens by antigen-specific suppressor T cells

Delayed-type hypersensitivity (DTH) against alloantigens can be induced by sc immunization with allogeneic cells. The induction of DTH can be suppressed by iv preimmunization of the mice with similar allogeneic spleen cells, provided the cells are irradiated before injection. This suppression is mediated by T cells. The suppressor activity can be induced not only by H-2-and non-H-2-coded antigens, but also by H-2 subregion-coded antigens. Suppression induced by K, I, or D subregion-coded antigens is specific for that particular subregion as well as for its haplotype. I-J-coded alloantigens were found to not be necessary for the induction of antigen-specific suppressor T cells. After restimulation of suppressor T cells by the "specific" alloantigens, the DTH to simultaneously administered third-party alloantigens becomes suppressed as well. This nonspecific suppression of DTH to third party "bystander" alloantigens also occurs when the specific and the third-party antigens are presented on separate cells, provided that both cell types are administered together at the same site. The simultaneous presentation of both sets of alloantigens during the induction phase of DTH only is sufficient to prevent the normal development of DTH to the third-party antigens.     

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.     

Studies on the induction of tolerance to alloantigens. I. The abrogation of potentials for delayed-type-hypersensitivity response to alloantigens by portal venous inoculation with allogeneic cells

The present study investigates the effect of portal venous (p.v.) administration of allogeneic cells on the capacity of delayed-type-hypersensitivity (DTH) reactivity to alloantigens. BALB/c mice were inoculated with C3H/He spleen cells via intravenous (i.v.) or p.v. route. Intravenous injection of C3H/He spleen cells into BALB/c mice resulted in appreciable DTH responses to C3H/He alloantigens. In contrast, p.v. inoculation of the same number of C3H/He cells not only failed to induce any significant anti-C3H/He DTH responses but also abolished the capability of the animals to develop DTH responses as induced by subcutaneous (s.c.) immunization with C3H/He spleen cells. Such suppression was alloantigen-specific, since p.v. inoculation of C3H/He spleen cells resulted in selective inhibition of anti-C3H/He DTH potential without suppressing DTH responses to C57BL/6 alloantigens. This tolerance was rapidly inducible and long-lasting. When spleen cells from tolerant mice were transferred i.v. into 600 R X-irradiated syngeneic recipient mice alone or together with normal BALB/c spleen cells, these tolerant spleen cells themselves failed to induce DTH responses but did not exhibit any suppressive effect on the generation of DTH responses induced by normal spleen cells co-transferred. These results indicate that tolerance was not necessarily associated with the induction of suppressor cell activity but rather was associated with the elimination or functional impairment of clones specific for alloantigens. The results are discussed in the context of a) the role of the liver in immune responses, b) cellular mechanisms underlying the tolerance induction, and c) potential application of this approach to the future transplantation immunology.     

Alloantigens placed into the anterior chamber of the eye induce specific suppression of delayed-type hypersensitivity but normal cytotoxic T lymphocyte and helper T lymphocyte responses

Intracameral inoculation of allogeneic B16F10 melanoma cells (C57BL/6) into LP/J mice resulted in progressively growing intraocular tumors and impaired delayed-type hypersensitivity (DTH) reactivity. Additional experiments showed that DTH responses were specifically down-regulated by splenic T suppressor cells. By contrast, subcutaneous inoculation of B16F10 melanoma cells induced significant DTH responses to the alloantigens expressed on the tumor cells and stimulated brisk rejection of the subcutaneously injected tumor cells. In spite of the T suppressor cell inhibition of DTH reactivity, significant cytotoxic T lymphocyte activity could be demonstrated in lymphoid cell suspensions from hosts harboring allogeneic intraocular tumors. The demonstrated cytotoxic T lymphocyte activity is particularly noteworthy because it occurs in the face of severely suppressed DTH responsiveness and thus implies that the intracameral presentation of alloantigens evokes a precise immunoregulatory process that selectively and concomitantly modulates specific cellular immune components; one immune process (cytotoxic T lymphocyte function) is stimulated whereas the other (DTH responsiveness) is down-regulated.     

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.     

Effects of pertussis toxin on delayed-type hypersensitivity responses and on the activity of suppressor T cells on the responses

Experiments were performed on mice to investigate the effects of pertussis toxin (PT) on delayed-type hypersensitivity (DTH) to ovalbumin (OA) and on the activity of suppressor T cells on the DTH (DTH-Ts). Mice immunized with alum-precipitated ovalbumin showed a transient DTH, which was determined as footpad swelling which disappeared 2 weeks after immunization. Maximal footpad swelling was observed 24 hr after DTH elicitation. On the other hand, when mice received PT (2 micrograms/mouse) at the time of immunization, the transient DTH became an enhanced and persistent DTH, which persisted for at least 4 weeks. In addition, the time of maximum footpad swelling was delayed from 24 to 48 hr after DTH elicitation. The immune spleen T cells from PT-treated mice showed a persistently high ability to transfer DTH into syngenic naive mice. DTH-Ts was induced in spleens of mice injected iv with OA-coupled syngeneic spleen cells. However, when these mice received PT at the time of suppressor induction, their spleen cells revealed considerably reduced suppressor activity. The activity of DTH-Ts was also reduced when DTH-Ts were either treated in vitro with PT or transferred into PT-injected recipient mice. From these results, interference with the suppressor function of DTH-Ts from PT was considered to be, at least in part, as an enhancing mechanism of DTH.     

T-T cell interaction in the induction of delayed-type hypersensitivity (DTH) responses: vaccinia virus-reactive helper T cell activity involved in enhanced in vivo induction of DTH responses and its application to augmentation of tumor-specific DTH responses

The role of antigen-specific helper T cells in augmenting the in vivo development of delayed-type hypersensitivity (DTH) responses was investigated. C3H/HeN mice were inoculated i.p. with vaccinia virus to generate virus-reactive helper T cell activity. These vaccinia virus-primed or unprimed mice were subsequently immunized subcutaneously (s.c.) with either trinitrophenyl (TNP)-modified syngeneic spleen cells (TNP-self), vaccinia virus-infected spleen cells (virus-self), or cells modified with TNP subsequent to virus infection (virus-self-TNP). Seven days later, these mice were tested for anti-TNP DTH responses either by challenging them directly with TNP-self into footpads or by utilizing a local adoptive transfer system. The results demonstrated that vaccinia virus-primed mice failed to generate significant anti-TNP DTH responses when s.c. immunization was provided by either virus-self or TNP-self alone. In contrast, vaccinia virus-primed mice, but not unprimed mice, could generate augmented anti-TNP DTH responses when immunized with virus-self-TNP. Anti-vaccinia virus-reactive helper activity was successfully transferred into 600 R x-irradiated unprimed syngeneic mice by injecting i.v. spleen cells from virus-primed mice. These helper T cells were found to be antigen specific and were mediated by Thy-1+, Lyt-1+2- cells. DTH effector cells enhanced by helper T cells were also antigen specific and were of the Thy-1+, Lyt-1+2- phenotype. Furthermore, vaccinia virus-reactive helper T cell activity could be applied to augment the induction of tumor-specific DTH responses by immunization with vaccinia virus-infected syngeneic X5563 tumor cells. T-T cell interaction between Lyt-1+ helper T cells and Lyt-1+ DTH effector T cells is discussed in the light of the augmenting mechanism of in vivo anti-tumor-specific immune responses.     

Differential effects of alloimmunization on T cells mediating graft-vs-host splenomegaly or the allogeneic effect in F1 mice.

Spleen cells from normal BALB/c mice or mice immunized 10 or 30 days previously with C57BL/6 spleen cells were tested for a) their capacity to produce graft-vs-host (GVH) reactions in newborn F1 mice and b) their capacity to produce an allogeneic effect in adult F1 mice immunized with Type III pneumococcal polysaccharide. GVH reactivity of alloimmune spleen cells obtained 10 or 30 days after immunization was significantly increased as compared to the reactivity of normal spleen cells in that a) at comparable cell doses, higher spleen indices were obtained with alloimmune cells than normal cells, and b) alloimmune cells produced severe runting at lower cell doses than normal cells. By comparison, the capacity of alloimmune spleen cells to produce an allogeneic effect was reduced 50% on a per cell basis as compared to normal spleen cells at both 10 and 30 days after immunization. These results give further evidence that T cells producing the allogeneic effect are distinct from the T cell populations which interact to produce GVH splenomegaly.     

A requirement for helper T cells in the induction of delayed-type hypersensitivity

This paper describes a model system for studying the role of helper T cells in the induction of delayed-type hypersensitivity (DTH). Cyclophosphamide- (CP) treated mice sensitized with antigen 3 days later develop high levels of delayed-type immunity; however, DTH cannot be demonstrated in mice that are sensitized with antigen 1 day after drug treatment. The inability to respond to antigen 1 day after CP treatment can be restored if either normal or low-dose primed spleen cells are transferred at the time of sensitization. Although irradiated (1500 rad) normal spleen cells are unable to restore DTH, such treatment has no effect on the primed spleen cell population. The lymphocytes responsible for restoring the DTH response were identified as T cells, in that treatment with anti-Thy-1.2 serum and C abrogated their effect. Furthermore, restoration of the DTH response was dependent on the presence of antigen at the time of lymphocyte transfer; irradiated primed cells could not transfer DTH alone. The DTH effector cells in reconstituted mice were identified as originating from the host and not from the transferred cell population. This was accomplished by using anti-H-2 serum to identify the source of the DTH effector cells after transferring parental (H-2b) irradiated primed spleen cells into CP-treated F1 mice (H-2b,k). Thus, the irradiated transferred cells are behaving as helper T cells and promoting the development of DTH effector cells in the host.     

Direct in vitro evidence for different susceptibilities to 4-hydroperoxycyclophosphamide of antigen-primed T cells regulating humoral and cell-mediated immune responses to sheep erythrocytes: a possible explanation for the inverse action of cyclophosphamide on humoral and cell-mediated immune responses

Suppressor T cells of humoral immune responses, effector T cells mediating DTH, suppressor T cells of DTH, and helper T cells of humoral immune responses, all with specificity to SRBC, were produced in mice. The biologic activity was tested in adoptive transfer experiments. In vitro treatment with different doses of 4-hydroperoxycyclophosphamide (4-HPCy) yielded the result that the various activities tested were not uniformly sensitive to the action of this drug: Suppressor T cells of humoral immune responses and effector T cells mediating DTH were resistant to doses of 4-HPCy that eliminated the activities of suppressor T cells of DTH and helper cells of the humoral immune response. These findings help to explain the various effects cyclophosphamide has on the in vivo immune response and may help to form a basis for the rational manipulation of the immune response by drugs that selectively affect different subgroups of immune cells.     

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.     

Prophylactic immunization against experimental leishmaniasis. V. Mechanism of the anti-protective blocking effect induced by subcutaneous immunization against Leishmania major infection

The responsiveness of BALB/c mice to protective i.v. immunization with 150,000-rad irradiated or heat-killed Leishmania major promastigotes can be totally suppressed by prior subcutaneous (s.c.) injection of the same "vaccine." Induction of this effect is leishmania specific for although prevention of protection against L. major infection can be obtained with either homologous or Leishmania donovani promastigotes, it does not follow s.c. administration of an immunogenic Trypanosoma cruzi epimastigote preparation. Multiple s.c. injections of irradiated L. major promastigotes do not inhibit the subsequent antibody response of any major isotype to i.v. immunization, but rather induce some priming. The same s.c. injections induced delayed-type hypersensitivity (DTH) reactivity that could be transferred locally or systemically, although it was weaker than in mice with cured infections. Parallel cell-mediated immunity (CMI) responses were also reflected in vitro in specific lymphocyte transformation assays. Despite this evidence of a DTH/helper type of T cell response, transfer of 5 X 10(7) viable T cell-enriched spleen cells from 4 X s.c. immunized donors to normal recipients completely abrogated the protective response to i.v. immunization. Conversely, T cell-depleted (anti-Thy-1.2 + C treated) cells were without effect. The inhibitory T cells were defined by monoclonal antibody pretreatment as possessing an Lyt-1+2-,L3T4+ phenotype. T cells from s.c. immunized donors were also shown, by mixed transfer experiments, to counteract completely the protective effect of T cells from i.v. immunized donors in 550-rad irradiated recipients. They were as potent as suppressor T cells from donors with progressive disease both in this capacity and in abrogating the prophylactic effect of sublethal irradiation itself. The similarities and differences between suppressor and immune effector T cells induced by s.c. or i.v. immunization and those arising in response to leishmanial infection itself are discussed.