Lymphocyte function in experimental African trypanosomiasis. IV. Immunosuppression and suppressor cells in the athymic nu/nu mouse

The role of T cells in the development and expression of antigen-nonspecific immunosuppression in experimental African trypanosomiasis was addressed. Nude ($\text{nu}\text{nu}$) C57BL/ 6 NIH mice and their thymus-bearing ($\text{nu}\text{+}$) littermates were infected with Trypanosoma rhodesiense and examined for suppression of splenic B-cell responses in vitro to the mitogen LPS. All animals developed splenic unresponsiveness to LPS. Further, both nu/nu and nu/ + infected mice displayed suppressor cell activity in their spleen cell populations upon transfer to normal uninfected mouse spleen cell cultures. On the basis of these findings we suggest that both the generalized immunosuppression and the development of suppressor cell activity in the spleens of mice infected with T. rhodesiense are T-independent processes.     

Impairment of primary in vitro response of New Zealand mouse spleen cells to a thymic-dependent antigen.

New Zealand Black (NZB) and NZB by New Zealand White (NZW) F₁ hybrid ($\text{B}\text{W}$) mice develop clinical signs of autoimmune disease between 6 and 10 months of age but spleen cells from these strains have a greatly reduced in vitro response to sheep erythrocytes (SRBC) as early as 5–6 weeks of age. This hyporesponsiveness can be only partially restored with 2-mercaptoethanol, allogeneic macrophages or spleen cells, or allogeneic factor. The response of NZB and $\text{B}\text{W}$ spleen cells to the thymic independent antigen DNP-Ficoll is nearly normal. The reduced in vitro SRBC response was found to be attributable to splenic T and B cells rather than macrophages. Macrophages from NZB mice were found to function normally. The in vitro behavior of NZB lymphocytes is very similar to non-autoimmune mice infected with common murine viral pathogens. NZB and $\text{B}\text{W}$ mice may be making an active immune response as early as 5 weeks of age.     

T-cell mediated suppression in the MRL mouse

MRL/lpr mice possess an autosomal recessive gene, lpr, which is associated with lymphoproliferation and acceleration of autoimmune disease. Lymphoproliferation has been ascribed to a single gene defect predominantly affecting the T-lymphocyte component of the immune system. MRL/++ mice do not possess the lpr autosomal recessive mutation and do not develop early lymphadenopathy. T-lymphocyte functional activity was studied in these mice using the polyclonal T-cell mitogens PHA and Con A. Our results indicated a significant suppression of the spleen and lymph node response of MRL/lpr mice to these polyclonal mitogens as compared to the MRL/++ response noted as early as 6 weeks of age. In addition, there was a progressive decline in the MRL/lpr spleen and lymph node cell mitogenic responses with increasing age. Spleen and lymph node cells from 20-week MRL/lpr mice were also relatively unresponsive in the mixed lymphocyte culture reaction as compared to cells from MRL/ ++ or BALB/c mice. The in vitro proliferative response of the MRL mice was further examined with respect to possible accessory cell modulation by both macrophages and T cells. It was found that in 20-week MRL/lpr lymph nodes a significant degree of suppression of lymphocyte proliferation could be mediated by the MRL/lpr T cell. Increased lymphocyte proliferation to a mitogenic signal could only be demonstrated in those MRL/lpr mice 3 weeks of age.     

Suppressor T-cell activity in MRL/Mp-lpr/lpr mice: differential effects on primary and memory antibody responses of MRL/Mp-lpr/lpr and MRL/Mp-+/+ spleen cells to thymus dependent and thymus independent antigens in vitro

We have previously shown that suppressor-T-cell (TS) activity in the spleens of autoimmune MRL/Mp-lpr/lpr (MRL/l) mice is increased after 2 months of age. The TS suppress the in vitro primary IgM response to the thymus-dependent (TD) antigen sheep erythrocytes (SRBC) of B and T cells from young congenic MRL/Mp-+/+ (MRL/n) mice which lack the lymphoproliferation (lpr) gene. The TS are nylon wool nonadherent, Thy 1.2 positive, and radiation sensitive. The studies presented here were done to further characterize the TS and to attempt to determine the mechanism of action of these cells. We found that increased TS activity was also present in the proliferating lymph nodes of old MRL/l mice but not in lymph nodes of young MRL/l or MRL/n mice. The splenic TS equally suppressed the primary IgM SRBC response of both young MRL/l and MRL/n B and T cells, indicating that MRL/l SRBC-specific B and T cells are not resistant to suppression. The IgM response of MRL/n B and T cells to the T-independent (TI) antigen trinitrophenyl conjugated to Brucella abortus (TNP-BA) was not suppressed by the TS, although the IgM response to TNP was suppressed when TNP was coupled to the TD carrier SRBC. The results of kinetics studies of TS expression showed that when the TS were added on Day 0 of culture the SRBC response was suppressed as early as Day 2 of culture; however, when the TS were added on Days 1, 2, or 3 of culture, the suppression was reduced. The TS suppressed the in vitro memory IgG response of spleen cells from MRL/n mice which had been primed with SRBC; the memory IgG responses of spleen cells from MRL/l mice were variably suppressed. Taken together, these results suggest that the TS suppress TH function in early events of antibody production and that some activated B or T cells may be resistant to the effects of the TS. Increased TS activity was not present in the spleens of aged New Zealand Black X NZ White (NZB/W) F1 mice. Possible reasons for the presence of increased TS activity in MRL/l mice and its relation to autoimmune disease is discussed.     

Ontogeny of murine B-cell responses to thymus-independent trinitrophenyl antigens.

The ontogeny of B-cell responsiveness to three thymus-independent trinitrophenyl (TNP) antigens has been examined in BALB/c mice in vivo and in vitro. When in vivo splenic plaque-forming cell (PFC) responses to TNP-conjugated lipopolysaccharide (TNP-LPS), Ficoll (TNP-Ficoll), and Brucella abortus (TNP-Brucella) were measured in neonatal and adult mice, a defined sequence of responsiveness was observed. Newborn mice responded well to TNP-LPS, but not to TNP-Ficoll or TNP-Brucella. Neonates injected at 1 day of age responded to TNP-LPS and TNP-Ficoll and mice 5 to 14 days of age responded to TNP-LPS, TNP-Ficoll, and TNP-Brucella. Furthermore, the antigen-reactive populations increased at different rates for the three antigens in the first 2 weeks of life. In vitro experiments confirmed the results obtained in vivo although slightly earlier responsiveness to TNP-Brucella was observed in vitro. PFC inhibition assays with free TNP hapten were performed so that avidity profiles could be examined in neonatal and adult anti-TNP PFC responses. The results clearly demonstrate that once a response becomes detectable in neonatal mice immunized with any of the three TI TNP antigens, fully heterogeneous or “adult-like” responses are found. In addition, experiments comparing avidity profiles in athymic (nu/nu) BALB/c mice and their normal (nu/+) littermates demonstrate that T cells are not required for the generation of fully heterogeneous anti-TNP PFC responses. These results indicate that B cells responsive to different TI TNP antigens mature at different times and at different rates during ontogeny. Late maturation events of such B cells do not include the acquisition of additional V-region specificities as detected in a PFC inhibition assay.     

Adjuvant-induced nonspecific supressor cells: in vitro and in vivo studies

The in vitro mitogen responses of spleen cells from mice injected ip with the nonantigenic adjuvant, Al(OH)₃, are markedly depressed. This depressed reactivity was found to be mediated by a population of nylon wool adherent, Fc-receptor-bearing suppressor cells. Suppressor cells were detected only in the spleens of the adjuvant-treated mice, as the response of lymph node cells to mitogenic stimulation in vitro was found comparable to that of normal controls. Moreover, elevated levels of suppressive activity could be detected in sera of Al(OH)₃-treated mice during the first week after adjuvant administration, which, however, did not correlate with either the long-lasting presence of suppressor cells or the in vivo normal immune response of the adjuvant-treated animals. Studies designed to test the effect of suppressor cells on the generation of splenic PFC in vivo revealed that both the direct and indirect PFC responses against SRBC inoculated iv were enhanced rather than suppressed, as compared to those of the normal controls. Furthermore, the level of cytotoxic lymphocytes generated in spleens of Al(OH)₃-treated mice immunized with allogeneic tumor cells was equal to or higher than that of the normal controls. In view of the present results, we feel that the concept that splenic, nonspecific suppressor cells (macrophages) are immunosuppressive in vivo as well as the in vivo relevance of in vitro findings should be carefully reevaluated.     

Expression of subregion and haplotype preference for H-2Kk restricted cytotoxic T-cell responses in vivo and at the level of the precursor frequencies

Several strains of mice bearing the H-2K^k allele were found to generate in vivo strong CTL responses against TNP-haptenated syngeneic cells, while several other strains of mice were found to generate comparably weak or no responses. C3H × DBA/2)F1 mice (H-2^k × H-2^d) and A/J mice with the recombinant haplotype $\text{H-2}{}^{\mathrm{<mtext>k</mtext><mtext>d</mtext>}}$ generated CTL responses in vivo that were completely restricted toward the H-2^k haplotype or the K end of the $\text{H-2}{}^{\mathrm{<mtext>k</mtext><mtext>d</mtext>}}$ haplotype, respectively. The CTL activity of C3H × DBA/2)F1 and A/J mice against haptenated H-2^k targets was found to be more than 25-fold higher than the CTL activity on H-2^d targets. The CTL responses in vitro under macroculture conditions showed, on the other hand, only a 3- to 6-fold higher cytotoxic activity against the haptenated H-2^k targets as compared with haptenated allogeneic or H-2^d targets; and limiting dilution experiments in microcultures revealed that the CTL precursor frequencies were only 2- to 3-fold smaller for TNP-haptenated H-2^d or haptenated allogeneic targets than for haptenated H-2^k target cells. This indicated that sufficient numbers of H-2^d-restricted and allorestricted CTL precursors were actually present in these strains, but did not develop detectable cytotoxic activity in vivo. The exceptional property of the H-2^k haplotype is, therefore, only partly determined by a difference in the CTL precursor frequencies, and to the larger extent determined at the level of the activation of the CTL response.     

Soluble factors from BCG-induced suppressor cells inhibit in vitro PFC responses but not cytotoxic responses.

A macrophage-like suppressor cell is present in the spleens of BCG-infected C57BL/6 mice. This suppressor cell is capable of suppressing both in vitro cytotoxic and PFC responses of normal C57BL/6 spleen cells. Suppression was not caused by changes in the kinetics of the responses or in the quantities of antigen required for stimulation. Suppression of the in vitro cytotoxic response could not be linked to any soluble mediator. In contrast, supernatants obtained from BCG spleen cell cultures, which failed to inhibit alloantigen-induced cytotoxic responses, suppressed the in vitro PFC response to SRBC by normal C57BL/6 spleen cells. It is postulated that either BCG-induced macrophage-like suppressor cells inhibit these in vitro responses via different mechanism(s) or these responses are regulated by different suppressor cell subpopulations within the monocyte/macrophage compartment of BCG spleen cells.     

Immunologic unresponsiveness of mouse spleen sensitized to allogenic tumors.

CS7BL/6 mice were sensitized with an ip injection of allogeneic P-815 mastocytoma cells. Fifteen days later the spleen cells of the tumor allosensitized mice were cultured and tested for their responsiveness to mitogens and alloantigens, and for their ability to generate cytotoxic cells in vitro. The results indicate that 15 day tumor-sensitized spleen cells are hypo-responsive in mixed lymphocyte culture (MLC) with DBA/2 or AKR as stimulating spleen cells. The cells which are hypo-responsive in MLC can proliferate in response to mitogens and they also can generate cytotoxic cells in vitro. MLC reactivity recovers in about 2–3 months which is $\text{1}\text{1}\text{2}\text{–2}\text{1}\text{2}$ months after the mice have rejected their tumors. The mechanism of MLC hypo-responsiveness was investigated. The results suggest the presence of a suppressor cell which does not appear to be a macrophage or a B-cell. The suppressor cell can be separated from the cytotoxic cell and therefore appears to be a noncytotoxic T-cell.     

Dysfunction of Ia-positive antigen-presenting cells in autoimmune mice

Antigen-presenting activity of spleen macrophages for T-cell activation was studied in vitro using autoimmune prone MRL/Mp-lpr/lpr (MRL/l) mice, and their normal counterparts, MRL/Mp-+/+ (MRL/n) mice. In vitro induction of trinitrophenyl (TNP)-specific proliferative T-cell response in lymph node lymphocytes from picryl chloride-painted mice was markedly impaired in MRL/l mice. The presenting activity of TNP-hapten by spleen macrophages for proliferative T cells was also impaired in MRL/l mice. The impairment of both T-cell and antigen-presenting macrophage activities was marked in older MRL/l mice, but not in younger ones. The impaired antigen-presenting activity of macrophages was not due to the development of suppressor macrophages. In accordance with the impaired antigen-presenting activity of macrophages the population of Ia-positive cells in spleen macrophages and the production of interleukin 1 by spleen macrophages were also reduced in older MRL/l mice. These results suggest that Ia-positive macrophages are impaired in autoimmune prone mice and that the dysfunction of Ia-positive macrophages plays an important role in the pathogenesis of autoimmune diseases.     

Concanavalin A-induced suppressor cell activity for T-cell proliferative responses: Autologous and allogeneic suppression in aging humans

Peripheral blood mononuclear cells from 48 healthy subjects of ages varying from 20 to 94 years were evaluated for the ability to generate suppressor cell activity following in vitro incubation with concanavalin A. The suppression of proliferative responses by autologous and young, allogeneic lymphocytes to phytohemagglutinin was assessed using suppressor/ responder cell ratios ($\text{S}\text{R}$) of 2:1 and 1:1 and by using a summation index. Inducible suppressor cell activity for autologous responder cells was comparable between 24 aged (76.0 ± 10.9 years) and 20 young (26.8 ± 4.6 years) subjects. However, aged subjects exhibited a significant decrease in suppressor cell activity ($\text{S}\text{R}\text{= 1}$) when allogeneic responder cells were utilized. Our results indicate that autologous inducible suppressor cell activity is preserved in the aged population, whereas allogeneic activity is impaired.     

Plaque-forming cells fater in vitro stimulation with theta-AKR antigen

Spleen cells of inbred mice strains carrying θ-C3H allele have been cultured in the presence of AKR thymus cells and their in vitro primary PFC response against thymic alloantigen θ-AKR was studied.The responses of a magnitude which was comparable with that obtained in previous in vivo experiments were obtained 4 days after stimulation. The strain-dependent variability of the magitude of anti-θ-AKR responses was observed in vitro. RR and C58/J spleen cells produced much more PFC than C57BL/6J and DBA/2J spleen cells. This was in agreement with previous in vivo studies on the genetic control of the anti-θ AKR responses.In the absence of AKR thymus cells, spleen cells of high responders, RR, developed in vitro PFC which released antibodies lytic to AKR thymus cells. Their number was ten-times lower than in stimulated cultures. Spleen cells of all strains tested produced also small numbers of PFC secreting antibodies against θ-identical allogenic thymus cells and even to syngenic thymus cells.     

Nucleoside-specific suppression in MRL/MP +/+ mice

The induction of nucleoside-specific nonresponsiveness was further studied in the autoimmune strain MRL/MP +/+ (MRL/n). Experiments were undertaken to determine (i) whether nucleoside-conjugated spleen cells are able to induce specific nonresponsiveness to T-dependent nucleoside antigens in MRL/n mice, and (ii) whether periodic treatment with nucleoside-conjugated spleen cells would retard the development of spontaneous anti-DNA antibodies and associated indicators of autoimmunity. The results show that nonresponsiveness to nucleoside antigens is inducable in male, but not in female, MRL/n mice. Nonresponsiveness in male MRL/n was transferable and mediated by T cells. Treatment of male MRL/n mice with nucleoside-conjugated spleen cells (NSC) appeared to attenuate the progress of autoimmune symptoms in experimental animals. These results are discussed in the context of recent studies exploring the etiology of autoantibody production and the loss of self-tolerance in murine models of autoimmunity.     

Schistosoma mansoni: Splenic lymphocyte responses of mice after initial exposure to highly irradiated cercariae

Inbred $\text{C}\text{57}\text{B}\text{1}\text{6}$ and CBA mice were immunized with ⁶⁰Co-irradiated (50 kR) Schistosoma mansoni cercariae. Based on the percentage reduction from controls in the numbers of adult parasites developing from a challenge cercarial exposure, the level of protection among immunized $\text{C}\text{57}\text{B}\text{1}\text{6}$ mice ranged from 56 to 74%, and among immunized CBA mice from 10 to 27%. In a longitudinal study, parallel in vitro comparisons of mitogen- and antigen-stimulated lymphocyte proliferative responses were performed with spleen cells from immunized and control mice of both strains. In contrast to decreased mitogen reactivity during a chronic, patent infection, immunization with irradiated cercariae resulted in no alteration in PHA and LPS responses in the reactivity of either strain. A vigorous antigen-specific reactivity was noted in the responses of immunized CBA mice. Additionally, a biphasic pattern of responsiveness characterized the CBA responses to antigens of cercarial, adult worm, or schistosomal egg origin. In comparison, there was a greatly diminished reactivity in immunized $\text{C}\text{57}\text{B}\text{1}\text{6}$ mice to the same antigens. Therefore, no obvious correlation existed in this model between the relative magnitude of antigen-specific responses between the two strains and the level of anti-schistosome immunity induced.     

Macrophages as effector cells of protective immunity in murine schistosomiasis: IV. Coincident induction of macrophage activation for extracellular killing of schistosomula and tumor cells

Peritoneal macrophages from Schistosoma mansoni-infected mice are activated both for nonspecific tumor cytotoxicity and for killing of skin-stage schistosomula in vitro. In the current study, mechanisms for induction of macrophage tumoricidal and schistosomulacidal activity have been compared. Examination of macrophages activated in vivo by BCG infection or C. parvum treatment, or in vitro by exposure to lymphokine prepared from antigen-stimulated BCG-immune spleen cells, showed that these effector functions were closely linked. Indeed, fractionation of lymphokine-rich supernatant fluids by Sephadex G-100 gel filtraction showed that activities responsible for induction of schistomula killing by inflammatory macrophages and for induction of tumoricidal activity cochromatographed as a single peak in the 50,000 MW region. Thus, development of macrophage-mediated cytotoxicity against these two extracellular (tumor cell or helminth) targets was coincident in several cell populations activated in vivo or in vitro. However, activation for tumoricidal and schistosomulacidal capacity appeared to be quantitatively dissociated in macrophages from mice with chronic schistosomiasis; those cells demonstrated low, yet significant, levels of larval killing ($\text{1}\text{3}$ to $\text{1}\text{5}$ those of BCG or lymphokine-activated cells) but maximal levels of tumor cell cytotoxicity. Furthermore, cytotoxicity by peritoneal cells from S. mansoni-infected mice was not increased in vitro by exposure to lymphokine. Identification of this functional alteration in S. mansoni-activated cells may help to clarify the role of macrophages in the partial immunity against challenge infection which is demonstrated by mice with chronic primary S. mansoni infection.     

Mechanisms of antibody formation: I. Early in vivo proliferation of mouse spleen T cells as an initial step in antibody formation

Spleen cultures prepared from mice injected 24 hr earlier with 2 × 10⁶?2 × 10⁸ sRBC and challenged in vitro with sRBC produced 10 times more anti-sRBC IgM PFC than cultures prepared from uninjected mice. The effect was specific for the particular species of foreign RBC injected in vivo. In vitro responses to TNP were also increased in spleen cultures prepared from animals injected 24 or 12 hr earlier with carrier RBC alone, directly implicating carrier-specific T cells in this process. Similar enhancements of PFC formation occurred in cultures prepared from mice which had been injected with sRBC 24 and 48 hr earlier, but which were exposed to lethal irradiation at 1 hr after injection of antigen, if their spleens were shielded extracorporeally during irradiation. This finding indicated that in vivo recruitment of antigen-reactive extrasplenic X-ray-sensitive cells from the circulating lymphocyte pool by the spleen could not account for the observed enhancement.Proliferation in the spleen of antigen-reactive T cells, commencing 12–20 hr after the administration of antigen, was demonstrated by the tritiated thymidine pulse technique. An 8-hr hot-pulse given to spleen cell cultures from normal animals at 20 hr after in vitro challenge with antigen did not affect the rate of generation of IgM-producing cells; however, administration of a similar pulse to cultures which were initiated at 12 or at 20 hr after the in vivo injection of sRBC eliminated the enhanced generation of PFC and delayed the in vitro response to sRBC by 24 hr.Spleen cell cultures were prepared from mice which had been injected in vivo with sRBC at 12, 20, and 70 hr earlier, and 8- to 10-hr hot pulses were given immediately after initiation of the cultures. The cultures were then challenged with sRBC-TNP; antibody responses to TNP were greatly reduced in hot-pulsed cultures prepared from mice injected in vivo with carrier RBC at 12 or 20 hr prior to initiation of the cultures. In contrast, antibody responses to TNP observed in hot-pulsed cultures prepared from mice which had been injected with carrier RBC at 70 hr prior to initiation of the cultures were generally similar to those of nonpulsed 70 hr control cultures. This result suggests that the onset of T helper cell proliferation begins within 12–20 hr after injection of antigen, but subsides in vivo within 70 hr. By that time, the antigen-reactive T cells have already differentiated to perform their helper function.In spite of the triggering of T-cell proliferation during the first 24 hr after injection of antigen, spleen cell cultures prepared from mice which had been injected 24 hr earlier in vivo with 2 × 10⁸ sRBC produced only minimal numbers of anti-sRBC PFC if no antigen was added to the cultures. The presence of unprocessed antigen thus appears to be a requirement for B-cell proliferation in vitro, even after T-cell division has been triggered. This finding is consistent with earlier suggestions that the function of “helper” T cells may not be limited to passive transport of antigenic determinants to B cells. Evidence is also presented to support the contention that the antigen-reactive T cell involved in this process may have to undergo cell division in order to develop “helper” capacity.     

Transfer of cell-mediated immunity with cell-free leukocyte extracts: II. Demonstration of antigen-specific and nonspecific components

Transfer of cell-mediated immunity was achieved with dialyzable cell-free extracts from lymphoid cells of mice primed to the contact sensitizing agent, 2,4-dinitrofluorobenzene (DNFB). The biological activity of the extract (Transfer Factor, TF) was analyzed in vivo by the ear thickness assay and in vitro by the macrophage migration inhibition (MMI) test and lymphocyte transformation using the soluble analog, sodium 2,4-dinitrobenzenesulfonate. Consistently positive responses occurred 20 hr following a single intravenous injection of 5 × 10⁷ lymphocyte equivalents per recipient. The most potent source of TF (memory TF) was lymph node cells obtained 30 days after primary exposure to DNFB. By contrast TF prepared at the peak of the response to DNFB was less potent which was shown to be due to the presence in it of a suppressor factor. Memory TF elicited macrophage inhibition factor production in naive lymph node cells whereas positive responses were only obtained in the ear thickness and lymphocyte transformation assays provided recipients had undergone prior subliminal sensitization. Specificity of TF was tested using picryl chloride and oxazolone as control antigens. Results from the MMI and ear thickness assays were consistent with the presence in Transfer Factor of an antigen-specific component. Its effects, however, on the proliferative response to antigen lacked specificity and depended on prior sensitization of recipients, rather than donors, to the inducing antigen. The target of the specific component was considered to be an Ly-1⁺, Ia^?, $\text{Ly}\text{2}\text{3}{}^{\mathrm{?}}$ T cell since MIF production and in vivo delayed hypersensitivity are known to be mediated by a T cell bearing this phenotype. Taken together these findings emphasize the value of using a battery of tests of cell-mediated immune function when studying soluble mediators such as Transfer Factor and suggest that the current system is a valid experimental model for analysis of the Transfer Factor phenomenon.     

In vitro T-lymphocyte proliferative response to mouse thyroglobulin in experimental autoimmune thyroiditis

The in vitro lymphocyte proliferative response to mouse thyroglobulin (MTg) was studied in good and poor responder mice in relationship to in vivo antibody formation and thyroid infiltration. CBA(H-2^k) and BALB/c(H-2^d) mice were immunized in the hind footpads with MTg incorporated into complete Freund's adjuvant (CFA). At weekly intervals up to 28 days, groups of mice were sacrificed. Their popliteal lymph nodes were cultured in vitro for proliferative response to MTg and their antibody levels and thyroid involvement determined. In good responder CBA mice, the proliferative responses to MTg were strongest on Days 8 to 14, where they were 9- to 14-fold over control levels, depending on the day of harvest. The response declined to 2- to 4-fold over background on Days 21 to 28, although high antibody levels were present throughout this period. The proliferative response was abrogated by anti-Thy-1 treatment, indicating its dependence on T cells. In poor responder BALB/c mice, no significant proliferative responses to MTg were observed at any time, although the animals displayed moderate levels of MTg antibody. The responses to PPD, in contrast, were similar in both strains, usually being 4- to 7-fold above background. Thyroid infiltration, like the proliferative response to MTg, was observed only in CBA mice. Thus lymphocyte proliferation at 8 to 14 days represents a reliable, early in vitro correlate of autoimmune thyroiditis induced with CFA as adjuvant.     

The effects of age on the immune response to type III pneumococcal polysaccharide (SIII) and bacterial lipopolysaccharide (LPS) in BALB/c, SJL/J, and C3H mice.

Type III pneumococcal polysaccharide (SIII) and bacterial lipopolysaccharide (LPS) were used to evaluate B cell and T cell regulatory functions in BALB/c, SJL/J, and C3H mice of various ages. It was found that the BALB/c and C3H mice could mount high level plaque-forming cell (PFC) responses to SIII at various ages through 110 weeks whereas the levels of the SJL/J PFC responses had begun to decline by the age of 42 weeks through the age of 80 weeks. BALB/c mice were also capable of producing strong PFC responses to LPS at various ages through 110 weeks whereas the comparable SJL/J PFC responses to LPS had declined by 80 weeks of age. By using anti-lymphocyte serum (ALS) and low-dose paralysis to SIII, it was shown that suppressor T cell activity was apparently greater in young BALB/c mice than in older BALB/c mice. It was also found that paralysis to SIII in BALB/c mice was easier to achieve at an early age. SJL/J mice were found to have the necessary B cell activity to respond to SIII through 80 weeks of age and the PFC responses could be greatly enhanced by ALS. Implications of the roles of regulatory T cells in aging are discussed.