Prophylactic immunization against experimental leishmaniasis. VI. Comparison of protective and disease-promoting T cells

In previous studies, we reported that mice immunized i.v. with lethally irradiated Leishmania major promastigotes developed substantial resistance to a subsequent L. major infection. However, such protection could be totally suppressed by prior s.c. injection with the same antigens. Both the protective immunity and the inhibition of its induction could be adoptively transferred with specific Lyt-2- T cells. Here, we present evidence showing that protection and disease promotion resulting from i.v. or s.c. immunization, respectively, are mediated by functionally distinct subsets of T cells. In a series of titration experiments, it was found that freshly isolated T cells derived from prophylactically i.v. immunized BALB/c mice were either protective (greater than 10(7) cells/recipient) or ineffective (less than 10(7) cells/recipient). No exacerbation of disease was observed at any dose. Conversely, T cells from mice immunized s.c. either accelerated disease development and inhibited protective immunization (greater than 10(7) cells/recipient) or had no effect (less than 10(7) cells/recipient). No protection was observed at any dose tested. In mixed transfer experiments, increasing numbers of T cells from s.c. immunized donors progressively inhibited the protective effect of T cells from i.v. immunized donors. Supernatant of T cell cultures from protectively immunized donors contained substantial macrophage-activating factor whereas such activity was not detectable in the supernatant of T cell culture from s.c. immunized donors. Analysis by flow cytometry showed that the spleen and lymph nodes of normal, i.v., or s.c. immunized BALB/c mice contained similar ratios of L3T4+ cells and Lyt-2+ cells.     

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.     

Different time course patterns of local expression of delayed-type hypersensitivity to sheep red blood cells in mice.

The delayed-type hypersensitivity (DTH) reaction, a peripheral expression of cell-mediated immunity is still a crucial in vivo immunological test. Nevertheless, the biological significance of its time course remains unclear. Thus, an exhaustive study of DTH was undertaken in mice immunized with increasing doses of sheep red blood cells (SRBC) inoculated intravenously (iv) or subcutaneously. The results showed that overall DTH reactions peaked at 18 hr except in mice iv immunized with the lowest doses (10(5) and 10(6)) and elicited at Day 4. The protracted DTH reaction was shown to be associated with an histological picture of tuberculin-type reaction. A part of the 18-hr DTH reaction is mediated by serum in mice inoculated with large doses of SRBC; nevertheless, numeration by limiting dilution analysis of circulating DTH cells showed that the frequency of these cells correlates with the 18-hr DTH level. The protracted DTH shown at 42 and 48 hr, 4 days after immunization with 10(5) and 10(6) SRBC, could not be transferred in naive recipients with immune spleen cells; it was independent of the antigen life span and did not result from immunization modulation at the bone marrow level on recruitable cells.     

Prophylactic immunization against experimental leishmaniasis. III. Protection against fatal Leishmania tropica infection induced by irradiated promastigotes involves Lyt-1+2- T cells that do not mediate cutaneous DTH

Protective immunity against fatal L. tropica infection in genetically vulnerable BALB/c mice can be induced by prophylactic immunization with irradiated promastigotes even when heat-killed. Such immunity is adoptively transferable transiently into intact or durably into sub-lethally irradiated (200 or 550 rad) syngeneic recipients by splenic T but not B cells. The effector T cells are of the Lyt-1+2- phenotype, devoid of demonstrable cytotoxic activity. The immune splenic T cell population expresses specific helper activity for antibody synthesis. A causal role for helper T cells in this capacity, however, seems unlikely, because it was shown in the accompanying paper that antibody does not determine the protective immunity against L. tropica. The immunized donors show no detectable cutaneous DTH or its early memory recall in response to live or killed promastigotes or a soluble L. tropica antigen preparation. Spleen, lymph node, and peritoneal exudate cells from protectively immunized donors similarly fail to transfer DTH locally or systemically. These cells also lack demonstrable suppressive activity against the expression or induction of DTH to L. tropica. Thus, protection against L. tropica induced by prophylactic i.v. immunization with irradiated promastigotes appears to be conferred by Lyt-1+2- T cells that are distinguishable from T cells mediating either both DTH and T help, or cytotoxicity.     

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.     

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.     

Delayed-type hypersensitivity response in mice to Pneumocystis carinii.

Resistance to Pneumocystis carinii infection appears to be mediated by T lymphocytes but the mechanism and subsets of T cells involved are poorly understood. We used the BALB/c mouse model to study the delayed-type hypersensitivity (DTH) response to rat P. carinii. Mice were sensitized to P. carinii for seven days and then challenged with P. carinii antigens in the right rear footpads and normal rat lung antigens in the left rear footpads. A typical DTH response was observed in the right footpads as evidenced by significant swelling and substantial mononuclear cell infiltration at 24-h post-challenge. The DTH response could be transferred to naive syngeneic mice by adoptively transferring spleen cells from P. carinii-sensitized mice. In addition, by using anti-thy-1, anti-mouse Ig, anti-L3T4 and anti-Lyt-2.2 monoclonal antibodies in in vitro cytolysis experiments, we were able to demonstrate that the DTH response was dependent upon T lymphocytes. The response appeared to require cooperation between both L3T4+ and Lyt 2+ subsets of T lymphocytes.     

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.     

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.     

Activation of T cells by glutaraldehyde-fixed erythrocyte antigens: radiosensitivity of cells mediating delayed-type hypersensitivity reactions in the mouse.

Mice immunized with glutaraldehyde-fixed sheep red blood cells (G-SRBC) show delayed-type hypersensitivity (DTH) reactions to G-SRBC or SRBC. The specificity of the DTH reaction of mice sensitized with glutaraldehyde-fixed antigens is similar to that found after sensitization with unfixed antigens. The dose-response curve for sensitization by glutaraldehyde-fixed SRBC was very different from the curve for normal SRBC. At low doses, both antigens were effective in sensitizing to show DTH but neither induced an antibody response. However, at high antigen doses, only the glutaraldehyde-fixed antigen was efficient in sensitizing to show DTH and it failed to raise an antibody titer. Spleen cells of mice sensitized with fixed RBC can transfer DTH locally but if the donor cells are irradiated (500 R), the transfer is abrogated. In contrast, the transfer of DTH by spleen cells of mice immunized with unfixed antigen is not affected by 500 R. The transfer of DTH by spleen cells of mice immunized with fixed antigen can be blocked by “in vitro desensitization” while the transfer of DTH by spleen cells from mice primed with normal antigen is resistant to “in vitro desensitization.” These results suggest that immunization of mice with different physical states of the same antigen can result in the activation of antigen-specific T cells which exhibit markedly different properties.     

Properties of cloned T cells that mediate delayed-type hypersensitivity against ovalbumin in mice

Cloned T-cell lines that mediate delayed-type hypersensitivity (DTH) against soluble protein antigen, ovalbumin (OA), were established in (C57BL/6 X DBA/2)F1 mice and their properties were examined. They induced antigen-specific delayed-type footpad reactions, characterized histologically by a predominant mononuclear cell infiltration, when transferred intravenously into syngeneic mice. Morphologically, they were medium or large lymphoblasts with granules in the cytoplasm and expressed Lyt 1 cell surface antigens. One of them proliferated antigen specifically under the presence of both C57BL/6 and F1 accessory cells, while others proliferated antigen specifically only under the presence of F1 accessory cells. They also produced macrophage-activating factor (MAF) and substances which mediate a DTH-like footpad inflammatory reaction with a maximum 6 hr after injection into the footpad of normal mice, when incubated in the presence of specific antigen and specific accessory cells in a serum-free medium for 24 hr. These results demonstrate that cloned DTH-effector T cells, established here against soluble protein antigen, are Lyt 1-positive, large lymphoblasts and that they produce MAF and footpad-reactive inflammatory substances antigen specifically under the presence of specific accessory cells.     

Influence of 2'-deoxyguanosine upon the development of DTH effector T cells and suppressor T cells in vivo

Subcutaneous (s.c.) immunization of mice with allogeneic spleen cells can induce delayed-type hypersensitivity (DTH) to both major and minor histocompatibility antigens. Intravenous immunization with allogeneic spleen cells, however, induces a poor state of DTH. Furthermore, i.v. immunization with allogeneic spleen cells, especially if they have been irradiated, induces suppressor T lymphocytes. These suppressor T cells are capable of suppressing the host-vs-graft (HvG) DTH reactivity that normally arises after s.c. immunization. Moreover, they can suppress the development of anti-host DTH effector T cells during graft-vs-host (GvH) reactions. These models for HvG and GvH DTH reactivity were used to study the influence of 2'-deoxyguanosine (dGuo) and guanosine (Guo) on the generation of DTH-reactive T cells and suppressor T cells in vivo. It was found that daily i.p. administration of 0.01 mg dGuo to mice immunized i.v. partially prevented the generation of suppressor T cell activity, whereas daily administration of 0.1 or 1 mg dGuo resulted in a complete abolition. Administration of dGuo has no effect on the anti-host DTH reactivity by spleen cells from nonsuppressed donors except for when a daily dose of 10 mg is administered. This dose proved to be toxic for precursors of DTH effector T cells. Daily i.p. injection of Guo had no effect on the generation of suppressor T cells nor on the generation of DTH effector T cells. The effect of dGuo was found to be due to a direct effect on suppressor T cells and not to the induction of contrasuppressor cells. These data suggest a differential sensitivity of DTH-reactive T cells and suppressor T cells for dGuo. Because suppressor T cells and DTH-reactive T cells require proliferation for expressing maximal functional activity in the systems used, both cell types probably have different enzyme activities involved in the purine metabolism and similar deoxycytidine kinase activities, but have different nucleotidase (5'NT) activities, those in suppressor T cells being the lowest. If so, suppressor T cells will accumulate deoxyguanosine triphosphate, which causes an inhibition of the ribonucleotide reductase activity and thus of the DNA synthesis by these cells.     

Prostaglandin-mediated suppression of delayed-type hypersensitivity to infected erythrocytes during Babesia microti infection in mice

The mechanism of suppression of delayed-type hypersensitivity (DTH) to intraerythrocytic Babesia microti which occurs during infection in mice was examined. The suppression was not specific for anti-parasite DTH; infected mice immunized and challenged with sheep red blood cells had a similar depression of anti-sheep red blood cell DTH. Sublethal or lethal irradiation did not significantly alter the suppression of the DTH response, and cyclophosphamide pretreatment of infected mice also had no effect on suppression. Multiple passive transfer experiments using serum or regional lymph node cells from immunized or infected and immunized (suppressed) donor animals failed to demonstrate any ability to transfer suppression of DTH. Adherent cells from the spleens or peritoneal exudates of suppressed mice, however, did significantly depress the ability of immunized mice to express a DTH response. The cells responsible for this suppression were Thy 1- and nonspecific esterase+. Treatment of suppressive cell populations with 10 micrograms/ml indomethacin for 24 hr in vitro abrogated their suppressive ability, and in vivo administration of indomethacin to suppressed mice also restored DTH to normal levels. By examining levels of prostaglandin E2 (PGE2) in supernates of cultured peritoneal exudate cells from immune or suppressed mice, it was shown that infected mice had peritoneal exudate cells which produced significantly more PGE2 than similar cells from immune mice. These data suggest that B. microti infection elicits synthesis of PGE2 by macrophage-like cells which results in suppression of DTH to parasite as well as heterologous antigens.     

Antigen-specific augmentation factor involved in murine delayed-type footpad reaction. IV. Effect of delayed-type hypersensitivity augmentation factor on in vitro induction of DTH

We found an antigen-specific factor capable of augmenting delayed-type hypersensitivity (DTH) in the serum of mice sensitized with heterologous erythrocytes to induce a delayed footpad reaction (DFR), or in the culture supernatant of the mixture of sensitized T cells and specific antigens. This factor (DTH augmentation factor; DAF) was confirmed to augment DTH in transferred recipients. In this paper, such an activity of DAF was further investigated using the system with in vitro induction and local transfer of DTH. DAF also augmented the primary in vitro induction of DTH, when spleen cells from mice transferred with the DAF-containing serum 12 hr previously or spleen cells incubated with the DAF-containing serum on ice for 2 hr were cultured with heterologous erythrocytes. DAF acted on the induction phase of DTH and augmented a typical DTH which was dependent on Thy-1-positive T cells. DAF showed antigen specificity, but was not assigned to conventional immunoglobulin. The activity of DAF was detected when nylon-wool nonadherent cells were incubated with DAF prior to the culture of those cells and antigens, but not detected when only nylon-wool adherent cells were incubated with DAF. Thus, DAF exerted its effect through binding to acceptor cells which were included in nylon-wool nonadherent spleen cells from normal mice.     

Trypanosoma cruzi: immune response in mice immunized with parasite antigens

The humoral and cellular immune responses were studied in mice immunized with flagellar fraction (F), F plus Bordetella pertussis as adjuvant (F-Bp), and microsomal (Mc) subcellular fractions from the epimastigote forms of Trypanosoma cruzi. The immune response was studied before and after the challenge with 50 bloodstream forms of T. cruzi, Tulahuén strain. The immunization with F-Bp, but not with Mc or F and Bp separately, protected mice, in terms of parasitemia and mortality, from the challenge with the parasite. Before the challenge, levels of specific antibodies in mice immunized with F-Bp were higher than in mice immunized with F or Mc. Antibody levels 17 days after the infection were similar in the three groups of mice while nonimmunized mice reached lower levels. Early during the infection nonimmunized infected mice lacked delayed-type hypersensitivity (DTH) responses to parasite antigens and to concanavalin A (Con A). Mice immunized with F-Bp, however, presented positive DTH responses to parasite antigens and Con A both, before and after the challenge with T. cruzi. DTH reaction was transferred with spleen cells. Mice immunized with Mc behaved similarly to infected nonimmunized animals in their reactivity to parasite antigens. These results indicated striking differences between protected and nonprotected mice in humoral and cellular immune responses during experimental T. cruzi infection.     

Effector phenotypes and mechanisms of antitumor immune reactivity of tumor-immunized and tumor-bearing mice in two syngeneic tumors.

By using two different syngeneic tumors, Meth A sarcoma and RL male 1 lymphoma of BALB/c origin, the present study was designed to investigate the subset(s) of T cells mediating in vivo antitumor immune responses and some of the effector mechanisms of in vivo protective immunity in BALB/c mice immunized against tumor or bearing tumor. Spleen cells from the mice immunized against Meth A tumor or bearing Meth A tumor inhibited the growth of Meth A tumor in the Winn assay. In the Meth A-immunized mice, L3T4+ (CD4+) cells played a major role in mediating the inhibitory activity against Meth A tumor growth, whereas in the Meth A-bearing mice, the antitumor protective immunity was mediated by both L3T4+ and Lyt-2+ (CD8+) cells. Spleen cells from the Meth A-immunized or Meth A-bearing mice were not able to generate cytotoxic T lymphocytes (CTL) directed against Meth A tumor after the in vitro restimulation of spleen cells with mitomycin C (MMC)-treated Meth A cells, while fresh spleen cells from the Meth A-immunized or Meth A-bearing mice were able to induce the strong delayed-type hypersensitivity (DTH) responses to Meth A tumor. The DTH response to Meth A tumor was mediated by L3T4+ cells in the Meth A-immunized mice and by both L3T4+ and Lyt-2+ cells in the Meth A-bearing mice. In the similar experiments performed in the RL male 1 lymphoma, the antitumor activity in spleen cells from the RL male 1-immunized or RL male 1-bearing mice depended on Lyt-2+ but not L3T4+ cells in the Winn assay. When spleen cells from the RL male 1-immunized or RL male 1-bearing mice were cultured with MMC-treated RL male 1 cells for 5 days, an appreciable CTL response to RL male 1 tumor was induced. These results suggest that the nature of tumor and/or tumor antigens determines which T cell subset is required to exhibit the protective immunity against tumor and thus the different effector mechanisms could be induced in the different tumor models. Furthermore, these data support the conclusion that antitumor T cell responses are affected by the immune state of host to tumor.     

Evanescent delayed-type hypersensitivity: mediation by effector cells with a short life span.

Four days after i.v. immunization of mice with optimal low doses of heterologous erythrocytes (2 x 10(5) RBC), strong delayed-type hypersensitivity (DTH) responses can be elicited in the footpad. At later intervals after immunization, DTH responsiveness is progressively diminished and replaced by 4-hr antibody-dependent reactions. These evanescent T cell-mediated DTH responses, which are progressively replaced by antibody-dependent reactions, resemble Jones-Mote type delayed hypersensitivity responses of humans and guinea pigs. Since higher doses of immunizing antigen activate suppressor mechanisms that inhibit DTH responses, we examined the possibility that the evanescence of DTH in mice immunized with an optimal low dose of antigen might also be due to suppression. Using techniques that could clearly demonstrate the suppression produced by high antigen doses, we failed to find evidence for either humoral or cellular suppression in optimally immunized mice with declining of DTH responses. Thus, it appears that the evanescence of produced by optimal low dose immunization with RBC may be due to an intrinsic short life span of the effector cells rather than to the activation of an identifiable shut-off mechanism.     

Regulatory mechanism of delayed-type hypersensitivity in mice. I. Properties of memory cpells and suppressor cells for delayed-type hypersensitivity against ovalbumin.

Delayed-type hypersensitivity (DTH) response in mice induced by sc injection of alum-absorbed ovalbumin (OA) was accelerated and enhanced by priming sc with a low dose of urea-denatured ovalbumin (UD-OA), 2 or more days earlier, whereas it was suppressed by priming sc with a high dose of UD-OA, 0 or more days earlier. The ability in primed mice to accelerate or suppress the DTH response could be transferred antigen specifically into cyclophosphamide (CY)-pretreated recipients or normal recipients by spleen cells from primed mice, but not by the T-cell-depleted spleen cells. Furthermore, the ability of spleen cells to transfer the acceleration or the suppression appeared transiently around 7 or 4 days after priming, although the acceleration or the suppression in donor mice persisted for a much longer time. Pretreatment with CY abolished the suppression of DTH response in high dose-primed mice and resulted in the acceleration of DTH response. These results suggest that the activity of DTH-related memory T cells which accelerate and enhance the response can be inhibited by suppressor T cells for the DTH response.     

Virus-specific delayed-type hypersensitivity (DTH). Cells mediating lymphocytic choriomeningitis virus-specific DTH reaction in mice

We had previously shown that the local lymphocytic choriomeningitis virus-induced delayed-type hypersensitivity (DTH) reaction in mice consists of two well delineated phases that are mediated by CD8+ and CD4+ T lymphocytes, respectively. These findings have been confirmed and extended by showing that the first CD8+ cell-dependent part of the response was enhanced by either the presence of CD4+ cells or systemic treatment with IL-2 and that it developed in the absence of detectable numbers of mononuclear phagocytes, whereas the later CD4+ cell part required monocytes or related elements. Furthermore, in the DTH reaction that was elicited with noninfectious viral Ag in mice previously immunized by infection, only the CD4+ cells participated. Thus, the two phases of the lymphocytic choriomeningitis-viral DTH reaction are principally different, which has to be taken into account when trying to assess the relevance of DTH during this virus infection.     

Experimental visceral leishmaniasis: production of interleukin 2 and interferon-gamma, tissue immune reaction, and response to treatment with interleukin 2 and interferon-gamma

During the first 2 to 4 weeks of progressive visceral infection with the intracellular protozoan, Leishmania donovani, spleen cells from BALB/c mice failed in response to leishmanial antigen to produce either of the activating T cell-derived lymphokines, interleukin 2 (IL 2) or gamma-interferon (IFN-gamma). Four weeks after infection, however, antigen-induced IL 2 and IFN-gamma secretion emerged and coincided with the onset of control over parasite replication and the subsequent killing of greater than 80% of intrahepatic L. donovani. The development of this immunosecretory activity correlated with the hepatic tissue response at the site of parasitized Kupffer cells. This response progressed from Kupffer cell fusion (week 1) to fusion plus a mononuclear cell infiltrate (week 2) to well-organized granuloma formation (weeks 4 to 8). In contrast, T cell-deficient nude BALB/c mice exerted no control over L. donovani, their spleen cells failed to generate antigen-induced IFN-gamma, and at 4 weeks, their livers were devoid of any tissue reaction. Since spleen cells from 2-week infected normal mice did not produce antigen-stimulated IL 2 or IFN-gamma, these mice were treated with recombinant (r) lymphokines. Various protocols using both high and low dose human rIL 2 had no antileishmanial effect. Hepatic parasite replication was completely halted, however, by macrophage-activating doses of murine rIFN-gamma. These results reemphasize that an intact T cell-dependent response is required for successful defense against L. donovani, indicate that this immune response can be measured at both the cellular (secretory) and tissue levels, and confirm that IFN-gamma can exert an antileishmanial effect in vivo.