Inhibition of antiskin allograft immunity induced by infusions with photoinactivated effector T lymphocytes (PET cells)

Induction of tolerance for skin allotransplantation requires selective suppression of the host response to foreign histocompatibility antigens. This report describes a new approach which employs pre-treatment with 8-methoxypsoralen (8-MOP) and ultraviolet A light (UVA) to render the effector cells of graft rejection immunogenic for the syngeneic recipient. Eight days after BALB/c mice received CBA/j skin grafts, their splenocytes were treated with 100 ng/ml 8-MOP and 1 J/cm2 UVA prior to reinfusion into naive BALB/c recipients. Recipient mice were tested for tolerance to alloantigens in mixed leukocyte culture (MLC), cytotoxicity (CTL), delayed-type hypersensitivity assays (DTH), and challenge with a fresh CBA/j graft. Splenocytes from BALB/c recipients of photoinactivated splenocytes containing the effector cells of CBA/j alloantigen rejection proliferated poorly in MLC and generated lower cytotoxic T-cell responses to CBA/j alloantigens in comparison with sensitized and naive controls and suppressed the MLC and CTL response to alloantigen from sensitized and naive BALB/c mice. In vivo, the DTH response was specifically suppressed to the relevant alloantigen in comparison with controls. BALB/c mice treated in this fashion retained a CBA/j skin graft for up to 42 days post-transplantation without visual evidence of rejection. These results showed that reinfusion of photoinactivated effector cells resulted in an immunosuppressive host response which specifically inhibited in vitro and in vivo responses that correlate with allograft rejection and permitted prolonged retention of histoincompatible skin grafts.     

Perturbation of the autoimmune network. II. Immunization with isologous idiotype induces auto-anti-idiotypic antibodies and suppresses the autoantibody response elicited by antigen: a serologic and cellular analysis

We report on the humoral and cellular events following autologous immunization against an idiotype (Id62) borne on a murine monoclonal autoantibody to thyroglobulin, and their impact on the autoantibody response to thyroglobulin. BALB/c mice with a state of active auto-anti-idiotypic immunity and challenged with thyroglobulin in complete Freund's adjuvant 2 wk after the last immunization with idiotype were found to have a suppressed autoantibody response. This suppression could be adoptively transferred to syngeneic x-irradiated recipients by using whole spleen cells from idiotype-primed mice. Transfer of separate T and B lymphocyte populations proved instrumental in disecting humoral from cellular events and in establishing that whereas B cells were required for transferring an intact anti-idiotype antibody response, T cells from idiotype-primed mice were necessary to transfer suppression. These findings contribute to our understanding of the interrelationship between antigen, idiotype, and anti-idiotype in the immune response to self-antigens, and the role of certain idiotypes in regulating autoimmune responses.     

A 23-kDa recombinant antigen of Cryptosporidium parvum induces a cellular immune response on in vitro stimulated spleen and mesenteric lymph node cells from infected mice

In the present study, we focused on a 23-kDa antigen, Cp23, which has been shown to be a major target of humoral immune responses in Cryptosporidium parvum infections and is present in both the sporozoite and merozoite stages. Recombinant Cp23 antigen was shown to stimulate a specific proliferative response by splenocytes and mesenteric lymph node cells from infected interferon gamma knockout BALB/c mice. Cp23 stimulation also induced TNF-alpha, IL-2, and IL-5 mRNA production by spleen cells from infected animals. In contrast, IL-12 mRNA was decreased by Cp23 stimulation compared with unstimulated splenocytes. These data suggest that, as with humoral responses, Cp23 is an important target of cellular immune responses in experimental C. parvum infections. The potential role of this antigen in conferring protective immunity is also discussed.     

Selective impairment of B cell function by Neisseria meningitidis

Spleen cells from CBA/J mice infected with Neisseria meningitidis displayed depressed in vitro plaque-forming cell (PFC) responses to T-dependent (sheep red blood cell; SRBC) and T-independent (TNP-LPS, TNP-Ficoll) antigens. The inhibition was observed over a wide range of antigen concentrations. The decreased responsiveness of splenocytes from infected mice was due to a selective impairment of B-cell function since helper-T-cell activity was intact in infected mice as shown by the ability of T-enriched lymphocytes to cooperate with normal B-enriched lymphocytes in the generation of an anti-SRBC response, accessory macrophage function was preserved since adherent spleen cells from bacteria-injected mice were shown to produce normal or increased levels of IL-1 and were able to cooperate with normal non-adherent spleen cells in the generation of PFC against SRBC. Addition of peritoneal cells from normal animals or extraneous IL-1 both failed to restore normal PFC responses in cultures of splenocytes from infected mice. Finally, B-enriched lymphocytes from infected mice produced poor anti-SRBC responses when cultured with either Con A supernatant or T-enriched lymphocytes from normal or infected mice. Cell-mixing experiments failed to detect the presence of suppressor cells in cultures of unfractionated spleen cells or B-enriched lymphocytes from infected mice. Therefore, the immunological unresponsiveness associated with a Neisseria meningitidis infection was attributed to a meningococcus-induced defect(s) in B-cell function. In vivo polyclonal B-cell activation leading to clonal exhaustion did not play a major role in the depression of humoral responses since meningococcal infection induced little or no polyclonal Ig secretion.     

Immunosuppression induced by attenuated Salmonella. Reversal by IL-4

We previously demonstrated that an aroA- strain of Salmonella typhimurium, which provides excellent protection against virulent Salmonella challenge, also rendered immunized mice unable to mount in vivo and in vitro antibody responses to heterologous Ag. Coculture studies using transwell plates indicated that suppression was mediated by soluble factors. The suppressive cells were identified as belonging to the monocytic linkage. Macrophage precursors as well as mature adherent macrophages mediated the observed suppression. In the present study, the mechanism of immunosuppression was investigated. Suppression was found to be genetically nonrestricted as spleen cells from immunized C3HeB/FeJ mice (H-2k) suppressed the anti-SRBC plaque-forming cell (PFC) responses of normal spleen cells from two MHC noncompatible mouse strains, BALB/c (H-2d) and C57BL/6 (H-2b). Time course experiments demonstrated that the addition of spleen cells from immunized mice to normal splenocytes as late as day 4 of a 5-day assay was still markedly suppressive. Furthermore, suppression of the PFC responses was accompanied by a profound inhibition of the capacity of immune splenocytes to produce IL-2 in response to in vitro stimulation by Con A. Coculture studies showed that immune spleen cells were able to suppress IL-2 production by normal splenocytes in a dose-dependent fashion. However, the suppressed PFC responses of immune spleen cells could not be reversed by the exogenous addition of up to 200 U/ml of IL-2, suggesting that immune splenocytes are also defective in their ability to respond to IL-2. In marked contrast, suppression of PFC responses was reduced by more than 50% by the addition of as little as 1 U/ml of IL-4 and was completely abrogated when 5 U/ml of IL-4 were added to in vitro cultures of spleen cells from immunized mice. The antisuppressive action of IL-4 appeared to be via its inhibitory effect on activated macrophages. The implications of the above findings are discussed.     

Immunomodulating activity of meningococcal antigens

A preparation of meningococcal antigens (MA) extracted in CaCl2, and containing mostly outer membrane proteins, was strongly mitogenic for murine B lymphocytes. Given to mice in vitro, MA markedly impaired subsequent in vivo T-cell responses of splenocytes. Suppression of normal T splenocytes in vitro occurred with both adherent (Ad) and nonadherent (NA) splenocytes from MA-sensitized mice. B cells were much less affected by the suppression induced by MA, and only Ad cells could convey in vitro the low level impairment of B-cell proliferation. Strong T-cell suppression associated with a B-cell mitogen is also produced by bacillus Calmette-Guérin (BCG) and Corynebacterium parvum. The possible role of these phenomena in meningococcal disease is discussed.     

Bystander sensitization to activation-induced cell death as a mechanism of virus-induced immune suppression

Viral infections which induce strong T-cell responses are often characterized by a period of transient immunodeficiency associated with the failure of host T cells to proliferate in response to mitogens or to mount memory recall responses to other antigens. During acute infections, most of the activated, proliferating virus-specific T cells are sensitized to undergo apoptosis on strong T-cell receptor (TCR) stimulation, but it has not been known why memory T cells not specific for the virus fail to proliferate on exposure to their cognate antigen. Using a lymphocytic choriomeningitis virus (LCMV) infection model in which LCMV-immune Thy 1.1(+) splenocytes are adoptively transferred into Thy 1.2(+) LCMV carrier mice, we demonstrate here that T cells clearly defined as not specific for the virus are sensitized to undergo activation-induced cell death on TCR stimulation in vitro. This bystander sensitization was in part dependent on the expression of Fas ligand (FasL) on the activated virus-specific cells and gamma interferon (IFN-gamma) receptor expression on the bystander T cells. We propose that FasL from highly activated antiviral T cells may sensitize IFN-gamma-conditioned T cells not specific for the virus to undergo apoptosis rather than to proliferate on encountering antigen. This may in part explain the failure of memory T cells to respond to recall antigens during acute and persistent viral infections.     

Cellular interactions in the cytotoxic T lymphocyte response to herpes simplex virus antigens: differential antigen activation requirements for the helper T lymphocyte and cytotoxic T lymphocyte precursors

The role and induction requirements of helper T lymphocyte responses to herpes simplex virus type 1 (HSV-1) was examined. Splenocytes from mice that had been primed in vivo with infectious HSV-1 can be restimulated in vitro with live or partially UV-inactivated HSV-1 to generate high levels of herpes virus-specific cytotoxic T lymphocyte (CTL) activity. By comparison, naive splenocytes or splenocytes taken from mice primed with heat-inactivated HSV-1 failed to generate CTL after in vitro viral stimulation. In addition, infectious HSV-primed splenocytes can be rendered unresponsive to secondary in vitro restimulation by pretreatment with anti-Lyt-1 antiserum plus complement. Spleen cells were taken from mice that had been primed and restimulated in vivo with infectious HSV-1. Two days after the second priming, splenocytes were prepared and irradiated. These cells were capable of assisting in the generation of CTL to varying degrees in all of the above unresponsive populations of cells. The irradiated cells did not produce detectable levels of CTL activity when cultured alone with antigen. Also, if the irradiated splenocytes were treated with anti-Lyt-1 plus complement before their addition to cultures, all restorative activity was ablated. In contrast, irradiated splenocytes from mice that had been primed and restimulated in vivo with either heat-inactivated or UV-inactivated HSV-1 were unable to provide help to naive or helper-depleted cultures. The failure to supply helper activity appears not to involve the preferential activation of suppressor cells, as evidenced by cell mixing experiments and the addition of concentrated, antigen-stimulated spleen cell supernatant fluids to secondary anti-HSV-1 splenocyte cultures. Proliferative assays using interleukin 2- (IL 2) dependent cell lines as a measure of relative helper activity indicated that the inactivated forms of HSV-1 were incapable of effectively enlisting helper activity. These experiments therefore suggest that the observed failure of heat-inactivated or UV-inactivated HSV-1 preparations to induce anti-HSV CTL responses reflects the inability of the HSV-1-specific subset of helper T lymphocytes to recognize these forms of the antigen.     

Mechanisms of suppressed cell-mediated immunity and impaired antigen-induced interleukin 2 production in granuloma-bearing mice

Pulmonary granulomas were induced in BALB/c mice immunized with methylated bovine serum albumin in complete Freund's adjuvant by the intratracheal injection of plain agarose beads or beads conjugated to specific antigen. Large hypersensitivity granulomas developed around antigen-coupled beads in immunized animals. Smaller but still prominent granulomatous reactions developed around plain beads in immunized mice. In nonimmunized animals, both plain and antigen conjugated beads produced very small granulomas. Granuloma formation in sensitized animals was associated with suppressed delayed-type hypersensitivity reactions induced by the footpad injection of specific and nonspecific antigens. Lymph node cells from sensitized granuloma-bearing mice with cutaneous anergy showed suppressed specific and nonspecific antigen-induced proliferative responses in vitro. These cells also showed suppressed interleukin 2 production in response to specific antigen. Although no soluble suppressive factor was detected in granuloma extracts, suppressor cells were found in lymph nodes of granuloma-bearing mice, which could inhibit antigen-induced production of interleukin 2 by lymph node cells from immunized mice. Antigen-specific immunoglobulin G antibody production was not suppressed in immunized granuloma-bearing mice. Previous studies from our laboratory have demonstrated migration inhibition factor and interleukin 1 activities in aqueous extracts prepared from granuloma-bearing lungs of immunized mice. These results and the findings reported here indicate that granuloma formation and the associated anergy observed in this system are primarily expressions of cell-mediated immunity; selective suppression of in vivo and in vitro expressions of cell-mediated immunity in granuloma-bearing mice may be due to impaired antigen-induced interleukin 2 production; and such impairment is caused by suppressor cells.     

Progressive depletion of peripheral B lymphocytes in 4-1BB (CD137) ligand/I-Ealpha)-transgenic mice

Interaction of 4-1BB (CD137) and its ligand (4-1BBL) is thought to positively regulate cell-mediated and humoral immune responses. We have prepared transgenic mouse strains that express 4-1BBL cDNA under the control of MHC class II I-Ealpha promoter. The 4-1BBL-transgenic mice show progressive splenomegaly and selective depletion of B220(+) B cells accompanied with low levels of circulating IgG and defective humoral responses to Ag challenge. In addition, splenocytes from the transgenic mice fail to provide stimulation for allogeneic T cells in both lymphoproliferative and CTL responses in vitro, whereas their T cells remain functionally normal. Our results reveal unexpected functions of 4-1BBL in the regulation of humoral immune responses and Ag presentation.     

Effect of antigen priming on T-cell suppression. I. Activity of Ly 1+2+ feedback suppressor T-cell precursors after isolation from competing Ly 2-T cells

Previous experiments have demonstrated that feedback suppression of murine antibody responses occurs in vitro after exposure of unprimed T-cell subsets to suppression-inducing signals from primed cells, resulting in suppression of primary and secondary IgM as well as IgG anti-SRBC responses. However, following priming with antigen when cells appear which are capable of inducing feedback suppression, the ability of unfractionated splenic T-cell populations to mediate detectable feedback suppression in vitro rapidly disappears, suggesting that priming alters the expression of feedback suppression at the same time as providing for its induction. In the present study, we have succeeded in isolating active feedback suppressor T-cell precursors (preTs) in the Ly 1+2+ and L3T4- T-cell populations from SRBC-primed as well as from unprimed mice, demonstrating that preTs are not lost after priming. The preTs isolated from primed mice resemble those isolated from unprimed mice in Ly and L3T4 phenotype, cell dose requirements, kinetics, level of suppression, and requirement for in vitro activation by primed cells. These results imply that antigen priming neither significantly depresses nor enhances the ability of Ly 1+2+ preTs to participate in feedback suppression and that activated suppressor effector cells are not detectable in the Ly 1+2+ splenic T-cell subset. Priming does, however, induce an enhancing activity in Ly 2-, L3T4+ T cells which appears to compete with feedback suppression and thus may account for the absence of detectable feedback suppression when unfractionated T cells from primed mice are the only source of preTs.     

Cellular immunity in chronic Theiler's virus central nervous system infection.

After (IC) inoculation of the DA strain of TMEV, SJL/J mice develop chronic CNS infection with marked mononuclear cell infiltration of spinal cord leptomeninges and white matter and concomitant demyelination. In the present study the temporal course of cell-mediated and humoral immune responses to virus were measured in this infection. It was shown that chronic TMEV infection is associated with the development of immunologically specific spleen cell reactivity as judged by in vitro incorporation of 3H-TdR into DNA in response to inactivated TMEV antigen. Spleen cell reactivity is first detectable about 2 months after infection, persists for at least 1 year, and correlates with the temporal development of serum-neutralizing antibody. The late development of sensitized spleen cells is not the result of an immunosuppressive effect of this virus infection since infected mice exhibit normal spleen cell proliferative responses to T cell mitogens and produce normal antibody responses to a heterologous protein antigen, sheep red blood cells. In addition, anti-viral antibody inhibits virus-induced spleen cell reactivity. Finally, the antigen-reactive lymphocyte subpopulation within the spleen responsible for proliferation to TMEV antigen are T cells and not B cells.     

T cell-induced Ig allotypic suppression in mice. II. Both CD4+ CD8- and CD4- CD8+ T cell subsets from sensitized Igha mice are required to induce suppression of Igh-1b allotype expression

We established the phenotype of T splenocytes (Ts) from Igha/a BALB/c mice sensitized against B splenocytes from the Ighb/b CB20 congenic mice that induce Igh-1b (IgG2a of the Ighb haplotype) suppression. This was achieved by studying the action of anti-T cell subset mAb on the capacity of Ts to induce this chronic allotypic suppression in Igha/b (BALB/c x CB20)F1 mice. The Ts were treated with cytotoxic anti-mouse CD4 or anti-mouse CD8 rat mAb in vitro before their injection into the Igha/b newborns or in vivo after their injection into the Igha/b newborns. Exposure to either anti-CD8 or anti-CD4 mAb in vitro or in vivo leads to loss of the capacity of Ts to induce Igh-1b allotypic suppression. Mixing CD4+-cell-depleted Ts and CD8+-cell-depleted Ts preparations restored the capacity of the cells to induce Igh-1b suppression. Thus, both CD4+ CD8- Ts and CD4- CD8+ Ts are required for the induction of this allotypic suppression. Bone marrow cells and B splenocytes from Igh-1b-suppressed adult Igha/b mice were shown to be able to durably express Igh-1b when transferred into irradiated Igha/a BALB/c hosts whereas whole spleen cells from such donors failed to do it. Abrogation of Igh-1b suppression by in vivo anti-CD8 mAb treatment was achieved in adult Igha/b heterozygotes but with a lower efficiency than in adult Ighb/b homozygotes, all being chronically Igh-1b suppressed. The CD4- CD8+ cell population essential for maintaining this suppression is resistant to in vivo 600 rad irradiation and seems to be slightly inhibited by in vivo administration of free Igh-1b.     

Defective production of interleukin 1 and interleukin 2 in patients with systemic lupus erythematosus (SLE)

The effects of local antigenic exposure on the responsiveness of systemic T cells were evaluated after C3H mice were given drinking water containing 6% bovine serum albumin (BSA) for 10 days and challenged sc with 1.0 mg BSA in adjuvant 28 days after the initiation of antigen feeding. During the first 28 days, no evidence of in vitro antigen-induced proliferation [( 3H]thymidine incorporation) was detected in whole lymphocyte populations from the peripheral lymph nodes (PLN), spleen, or mesenteric nodes. In contrast, PLN cells treated with anti-Lyt-1 plus complement (C) had a significant proliferative response only if the cells were obtained during the first 6 days of antigen ingestion. Lymphoid cells from the same animals, treated with anti-Lyt-2 and C, did not respond to antigen. Two or 4 days after the injection, given on day 28, whole PLN cell populations from antigen-fed mice showed proliferation. No response was observed with PLN cells obtained 8 days after injection. Shortening the interval between the initiation of feeding and parenteral challenge partially restored proliferative responses detected 8 days after injection. Cultures prepared 4 days after simultaneous oral and parenteral antigenic exposure showed proliferation equal to or greater than cultures from mice that received only the injection. These data show that systemic T cell responsiveness is not eliminated by ingestion of soluble antigen, but rather is modulated in a manner previously detected in the humoral immune system.     

Distinct immunologic specificity of tumor regression mediated by effector cells isolated from immunized and tumor-bearing mice

Sensitized T lymphocytes can mediate potent antitumor effects when transferred to tumor-bearing animals. Employing the MCA 105 and MCA 106 sarcomas, we were able to generate antitumor effector cells by immunization of syngeneic mice with tumor cells admixed with Corynebacterium parvum. These immune splenocytes could be further sensitized and expanded in culture by the in vitro sensitization (IVS) method utilizing tumor stimulator cells and IL-2. Adoptive immunotherapy of pulmonary metastases mediated by noncultured splenocytes from immunized mice or immune IVS cells showed exquisite specificity between the two sarcomas. These results demonstrate the presence of tumor-specific antigens on MCA 105 and MCA 106 tumor cells which can serve as target molecules for immunotherapy. Recently, we have generated therapeutic T lymphocytes from mice bearing progressively growing tumors by the IVS method. However, IVS cells from tumor-bearing mice showed cross-reactivity between the MCA 105 and 106 sarcomas in adoptive immunotherapy experiments. Since these IVS cells did not affect other control tumors, the limited cross-reactivity suggests the presence of common tumor-associated antigens on MCA 105 and MCA 106 tumor cells which can also serve as the target for tumor rejection. Therefore, immune responses to progressive tumor growth and to immunization are distinct with respect to antigen recognition by T lymphocytes.     

Differences in the regulation of humoral responses between mice infected with Trypanosoma cruzi and mice administered T. cruzi-induced suppressor substance

In the present study, the effects of Trypanosoma cruzi and the T. cruzi-induced serum suppressor substance (SSS) on antibody responses were compared. Although infection with T. cruzi led to an alteration in T cell helper activity and a reduced specific B cell precursor frequency, SSS did not have a similar effect on either of these cell populations. The characteristics of the altered T cell helper activity was further investigated, and it was found that helper activity appeared earlier in infected mice than in normal or SSS-suppressed mice, and less antigen was required for optimal elicitation of T helper cells in infected mice. The potency of T cell helper activity also was shown to differ, and in the order T. cruzi-infected 6E normal 6E SSS-suppressed mice. It was found that spleen cells from T. cruzi-infected mice elaborated more potent specific helper factors than spleen cells from normal or SSS-suppressed mice, but did not produce a detectable nonspecific helper factor in vitro. Finally, the addition of B cells from low-dose primed, T. cruzi-infected mice to cultures of normal spleen cells resulted in subnormal responses to the priming antigen (sheep erythrocytes) but not to another unrelated antigen (trinitrophenyl-haptenated Brucella abortus), whereas similarly sensitized B cells from normal or SSS-suppressed mice caused no such effect.     

IgE peptide-specific CTL inhibit IgE production: a transient IgE suppression model in wild-type and HLA-A2.1 transgenic mice

Effect of IgE peptide-specific CTL on IgE antibody production was studied in mouse models. CTL elicited in B6.A2Kb tg mice against a human IgE peptide nonamer, pWV, lysed human IgE-secreting U266 myeloma cells and inhibit IgE production by these cells. U266 transfected with mouse A2Kb transgene (U266-A2Kb) were optimally lysed by these CTL, because the α3 domain of A2Kb interacts well with the CD8 co-receptors. The CTL generated were more effective in inhibiting IgE production by U266-A2Kb cells than lysing these cells. IgE production by and progression of U266 myeloma were suppressed in B6.A2Kb tg mice rendered tolerant to these cells and vaccinated with pWV along with CpG. We also studied the CTL response elicited in wild-type mice by a mouse nonameric IgE peptide, PI-1, along with CpG. This treatment caused a transient suppression of the IgE response in mice previously sensitized to an antigen. In mice treated with this regimen repeatedly, the IgE response was fully recovered 20 days after each treatment. Notably, while IgE peptide/CpG-treated mice remained unresponsive to antigen challenge in vivo, antigen-specific IgE production can be elicited by antigen in cultured splenocytes from these mice. Moreover, IgE peptide/CpG also inhibited an on-going IgE response, including IgE production by bone marrow cells. Taken together, these observations indicate that a CTL-based IgE peptide vaccine targeting IgE-secreting B/plasma cells may be safely employed as a therapeutic approach for suppressing IgE production.     

Cadmium exposure of rainbow trout, Salmo gairdneri Richardson: effects on immune functions

Differential leucocyte counts, phagocytosis, humoral antibody response and the in vitro blasto-genetic response to mitogens (lipopolysaccharide and Concanavalin A) and to an antigen ( Vibrio anguillarum ) were studied in rainbow trout exposed to 0,0.7 or 3.6 μg Cd 1⁻¹ for 12 weeks.
Although the fish did not exhibit any clinical or histological changes, cadmium exposure was found to affect two of the immune parameters measured. The cellular response of fish immunized with V. anguillarum to the homologous antigen was significantly lower for splenocytes obtained from fish exposed to cadmium for 9 weeks (3.6 μg Cd 1⁻¹ group) than for splenocytes obtained from non-exposed fish. Conversely, the humoral antibody response to V. anguillarum O-antigen was higher in the 3.6 μg Cd 1⁻¹ group than in the non-exposed group. Protective immunity of fish vaccinated against V. anguillarum was equally as good in the cadmium-exposed group as in the non-exposed group. No cadmium-induced changes in differential leucocyte counts or in the proportions of phagocytic cells were observed.     

In vitro regulation of the pathogenic autoantibody response of New Zealand black mice. I. Loss with age of suppressive activity in T cell populations

An investigation of the regulation of specific anti-self responses was initiated with the development of an in vitro system in which spleen cells from NZB mice were stimulated by syngeneic mouse erythrocytes (MRBC) to produce MRBC-specific autoantibody-secreting cells. The response was measured by a modification of the focus-forming cell (FFC) assay, which enumerates cells secreting IgG, which specifically bind MRBC. Spleen cells from 9- to 12-mo-old NZB mice developed MRBC-specific FFC after 3 to 5 days in culture with MRBC. Few FFC were detected in the absence of MRBC in culture. Spleen cells from young (1- to 4-mo-old) NZB mice developed few if any FFC. Spleen cell populations containing T cells from young NZB mice suppressed this anti-MRBC response, whereas B cell populations from these young mice did not. In contrast, spleen cells, including T cell-enriched populations from old, Coombs'-positive mice were not capable under the same conditions of producing equivalent suppression of this in vitro autoimmune response. These data suggest that a population of suppressor T cells that may control the autoimmune anti-MRBC response in young NZB mice is lost, or else its activity is masked in old NZB mice that are actively producing anti-MRBC antibody.     

Induction of protective immunity against Schistosoma mansoni by a nonliving vaccine. III. Correlation of resistance with induction of activated larvacidal macrophages

Mice protected against Schistosoma mansoni infection by intradermal (i.d.) immunization with nonliving larval or adult worm antigens plus bacterial adjuvant developed 24-hr skin test responsiveness to schistosome antigens with the histologic features of delayed hypersensitivity. Intraperitoneal antigen injection elicited a mononuclear cell-enriched exudative population containing macrophages activated for direct cytotoxicity against schistosomula and tumor cell targets. This was likely to be due to in vivo exposure to macrophage-activating lymphokines, since these cells were unresponsive to further lymphokine stimulation in vitro and splenocytes from immunized mice reacted to specific in vitro antigen challenge by production of lymphokines capable of conferring larvacidal activity upon control macrophages. In contrast, mice treated with schistosome antigens by i.v. injection, which were not protected against challenge infection, failed to develop delayed hypersensitivity or activated macrophages in response to specific antigen challenge in vivo, and the titers of macrophage-activating lymphokine produced by in vitro antigen-stimulated splenocytes from these mice were threefold to fourfold lower than those produced by cells from animals immunized by the i.d. route. Thus, sensitization for cell-mediated immune responses including lymphokine production and macrophage activation correlated with induction of resistance to S. mansoni in this model of vaccination.