H-2-linked Ir gene control of T cell recognition of the Sm nuclear autoantigen and the aberrant response of autoimmune MRL/Mp-+/+ mice

We have examined T cell recognition of the nuclear autoantigen Sm. Rabbit Sm-primed cells from autoimmune MRL/Mp-+/+ (+/+) mice and from all normal strains tested were able to proliferate to rabbit Sm in vitro. In contrast, the reactivity of normal strains to Sm of murine origin was genetically restricted; only H-2f strains B10.M and A.CA, and H-2s strains B10.S and A.SW could recognize mouse Sm, suggesting that responsiveness to mouse Sm was under the control of H-2-linked Ir genes. Although five Iak-bearing normal strains (B10.A, B10.A(2R), B10.BR, A/Sn, and CBA) did not recognize mouse Sm, autoimmune +/+ (Iak) mice were responders. The responsiveness of the +/+ mice to Sm was probably not due to differences in their Iak region, compared with other strains, because the Iak region of normal strains and the autoimmune +/+ strain were indistinguishable by interstrain MLC, immune response gene product function, and recognition by anti-Iak mAb. Inhibition of Sm-induced proliferation by mAb demonstrated that T cells from autoimmune +/+ mice, responder normal strains, and nonresponder normal strains recognized rabbit and mouse Sm in the context of I region-encoded products. The T cell response to Sm antigen in normal mice is therefore Ia region restricted and, for the murine antigen, under Ir gene control. Autoimmune mice that spontaneously make anti-Sm antibodies (+/+) also perceive Sm in an Ia-restricted manner, but their responder status abrogates H-2-linked Ir gene control.     

Altered expression of self-reactive T cell receptor V beta regions in autoimmune mice.

Intrathymic tolerance results in elimination of T cells bearing self-reactive TCR V beta regions in mice expressing certain combinations of I-E and minor lymphocyte stimulatory (Mls) phenotypes. To determine if autoimmune strains of mice have a defect in intrathymic deletion of self-reactive TCR V beta regions, expression of V beta 3, V beta 6, V beta 8.1, and V beta 11 were examined in lpr/lpr and +/+ strains of mice; MRL/MpJ(H-2K, I-E+, Mlsb,), C57BL/6J(H-2b, I-E-, Mlsb,), C3H/HeJ(H-2k, I-E+, Mlsc), AKR/J(H-2k, I-E+, Mlsa); and in autoimmune NZB/N(H-2d, I-E+, Mlsa) and BXSB(H-2b, I-E-, Mlsb) mice. The results suggest that, during intrathymic development, self-reactive T cells are deleted in autoimmune strains of mice as found in normal control strains of mice. However, the TCR V beta repertoire is skewed in autoimmune strains compared to normal strains of mice. For example, MRL-lpr/lpr mice, but not other lpr/lpr strains, had increased expression of V beta 6 relative to expression in control MRL(-)+/+ mice, which is associated with collagen-induced arthritis. These data are consistent with a model of normal affinity for negative selection of self-reactive T cells in the thymus of autoimmune strains of mice followed by expansion of autoreactive T cell clones in the peripheral lymphoid organs. The peripheral lymphoid organs of lpr/lpr mice contain an expanded population of abnormal CD4-, CD8-, 6B2+ T cells. Elimination of self-reactive peripheral T cells suggests that these abnormal cells are derived from a CD4+ subpopulation in the thymus. Flow cytometry analysis of peripheral lymph node T cells from MRL-lpr/lpr mice reveal three populations of CD4+ T cells expressing low, intermediate and high intensity of B220 (6B2). This supports the hypothesis that in lpr/lpr mice, self-reactive CD4+ T cells are eliminated in the thymus, and that these cells lose expression of CD4 and acquire expression of 6B2 in the periphery.     

Preferential use of a T cell receptor V beta gene by acetylcholine receptor reactive T cells from myasthenia gravis-susceptible mice.

Experimental autoimmune myasthenia gravis (EAMG) is an important model for testing current concepts in autoimmunity and novel immunotherapies for autoimmune diseases. The EAMG autoantigen, acethylcholine receptor (AChR), is structurally and immunologically complex, a potential obstacle to the application of therapeutic strategies aimed at oligoclonal T cell populations. Inasmuch as we had previously shown that the clonal heterogeneity of T cell epitope recognition in EAMG was unexpectedly limited, we examined TCR V beta expression. AChR primed lymph node T cells and established AChR reactive T cell clones from EAMG-susceptible C57BL/6 (B6; H-2b, Mls-1b) mice showed preferential utilization of the TCR V beta 6 segment of the TCR. After in vivo priming and in vitro restimulation for 7 days with AChR or a synthetic peptide bearing an immunodominant epitope, V beta 6 expressing lymph node cells (LNC) were expanded several-fold, accounting for up to 75% of recovered viable CD4+ cells. The LNC of B6.C-H-2bm12 (bm12; H-2bm12, Mls-1b) mice, which proliferated in response to AChR but not to the B6 immunodominant peptide, failed to expand V beta 6+ cells. Inasmuch as nonimmune bm12 and B6 animals had similar numbers of V beta 6+ LNC (4-5%), this suggested that structural requirements for TCR recognition of Ag/MHC complexes dictated V beta usage. Results concerning peptide reactivity and V beta 6 expression among T cells from (B6 x bm12)F1 animals also suggested that structure-function relationships, rather than negative selection or tolerance, accounted for the strain differences between B6 and bm12. To examine the potential effects of thymic negative selection of V beta 6+ cells on the T cell response to AChR, CB6F1 (H-2bxd, Mls-1b; V beta 6-expressing) and B6D2F1 (H-2bxd, Mls-1axb; V beta 6-deleting) strains were analyzed for AChR and peptide reactivity and V beta 6 expression. Both F1 strains responded well to AChR but the response of B6D2F1 mice to peptide was significantly reduced compared to CB6F1. Short and long term cultures of peptide-reactive B6D2F1 LNC showed no expansion of residual V beta 6+ cells, although similar cultures of CB6F1 LNC were composed of more than 60% V beta 6+ cells. The results from the F1 strains further indicated that the T cell repertoire for peptide was highly constrained and that non-V beta 6 expressing cells could only partially overcome Mls-mediated negative selection of V beta 6+ TCR capable of recognizing peptide.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cell cycle analysis of lymphocyte activation in normal and autoimmune strains of mice

The spontaneous spleen cell proliferation and the proliferation induced by in vivo or in vitro stimulation with such polyclonal B cell activators (PBA) as LPS, poly rI.rC, and anti-mu were studied in normal and autoimmune mice. The various murine models of autoimmunity differ in the level of naturally occurring splenic cellular hyperactivity as well as in the ability of their spleen cells to be further stimulated in vitro by polyclonal stimulators. Both the NZB strain and the MRL/Ipr strain had markedly increased numbers and percentages of spontaneously proliferating spleen cells, whereas the BXSB strain did not. Nonautoimmune strains were found to have very small numbers of activated cells in the spleen. However, such normal strains could be induced in vivo to mimic the natural splenic hyperactivity observed in older NZB and MRL/Ipr autoimmune strains by the injection of polyclonal B lymphocyte stimulators. In contrast, old hyperactive NZB mice were not further induced to undergo proliferation by in vivo administration of such stimulators. Density-separated, T depleted, spleen cells of normal and autoimmune mice were stimulated in vitro with PBA in 48-hr cultures. Cells from old MRL/Ipr and NZB mice were abnormal in both the anti-mu response and the LPS response; BXSB mice had normal anti-mu responses. These studies suggest that there is no prerequisite for spontaneous splenic hyperactivity in the development of autoimmunity. In addition, different PBA stimulate separate subsets of B cells that differ in their state of activation in the various autoimmune strains. Finally, different B cell subsets appear to be abnormal in different types of autoimmune mice.     

Abnormal polyclonal B cell activation in NZB/NZW F1 mice

Spleen cells from autoimmune (10-mont-old) NZB/NZW (B/W) mice failed to generate appreciable numbers of antibody-forming cells (AFC) in vitro to TNP-substituted sheep erythrocytes in response to the polyclonal B cell activators (PBA), LPS and PPD, despite normal DNA synthetic responses to these agents and normal AFC responses to TNP-Ficoll. The failure to respond to PBA in old B/W mice was not due to suppressor T cells since anti-brain-associated-theta-treated spleen cells still failed to generate AFC in response to PBA. The defect was age-related since cells from young B/W mice generated vigorous AFC responses to PBA. It is suggested that the failure of the spleen cells of old B/W mice to generate AFC is a result of in vitro polyclonal B cell activation in the course of autoantibody formation.     

Responses of B cells from autoimmune mice to IL-5

Three strains of mice (NZB/W F1 X NZW (NZB/W), BXSB, and MRL/Mp-lpr/lpr (MRL/lpr] develop an autoimmune disease that is clinically and immunologically similar to human SLE. A characteristic of these mice is polyclonal B cell hyperactivity. To explore whether this may be related to hyper-responsiveness to B cell stimulatory factors, we investigated the proliferative and secretory responses of B cells from these mice to semi-purified natural and rIL-5, a major regulator of B cell development in the mouse. As this lymphokine stimulates growth and differentiation of activated B cells, attention was focused on in vivo-activated B cell populations, obtained from the interface of 50/65% Percoll density gradients, from normal or autoimmune mice. This cell population from NZB/W mice secreted IgM and incorporated [3H]TdR at significantly higher levels in response to IL-5, and was more sensitive to IL-5, than a comparable population from several normal murine strains. NZB/W female and male mice displayed heightened responses to IL-5, indicating that this is characteristic of the strain in general and is not associated with the accelerated severe disease of the females. Small resting B cells from NZB/W and normal mice were insensitive to IL-5 stimulation. In contrast to NZB/W mice, no difference was observed in the magnitude of either proliferative or Ig secretory responses between in vivo-activated B cell populations from autoimmune BXSB and MRL/lpr or normal mice. Thus, B cell hyper-responsiveness to IL-5 is a characteristic of NZB/W mice but not of two other lupus-prone murine strains. As one unique feature of NZB/W mouse B cells compared to normal and other autoimmune B cells is an elevated proportion of Ly-1+ B cells, the possibility of IL-5 hyper-responsiveness being associated with this B cell subpopulation was investigated. Fluorescence-activated cell sorter sorted Ly-1+ and Ly-1- B cells both responded to IL-5, however Ly-1+ B cells consistently showed a higher stimulation index in both proliferative and Ig secretory responses to this lymphokine.     

IgG anti-DNA autoantibodies within an individual autoimmune mouse are the products of clonal selection

Although mice from almost all inbred strains produce IgM anti-DNA antibody in response to B cell mitogens, only (NZB x NZW)F1 mice and mice from other strains that are genetically predisposed to autoimmunity spontaneously produce anti-DNA antibody of the IgG isotype. Because (NZB x NZW)F1 mice display marked B cell hyperactivity, anti-DNA antibody production in these mice has been thought to result from spontaneous, polyclonal B cell activation. Although this may be true for IgM anti-DNA antibodies, our results demonstrate that IgG anti-DNA antibodies are not polyclonal. Rather, IgG anti-DNA autoantibodies within an individual autoimmune mouse are oligoclonal and somatically mutated. These results demonstrate that IgG anti-DNA autoantibodies are the products of clonally selective B cell stimulation and exhibit the same characteristics as secondary immune antibodies to conventional immunogens: they are IgG, they are clonally restricted, and they are somatically mutated.     

Genetic control of T and B lymphocyte activation in nonobese diabetic mice.

Type 1 diabetes in nonobese diabetic (NOD) mice is characterized by the infiltration of T and B cells into pancreatic islets. T cells bearing the TCR Vbeta3 chain are disproportionately represented in the earliest stages of islet infiltration (insulitis) despite clonal deletion of most Vbeta3(+) immature thymocytes by the mammary tumor virus-3 (Mtv-3) superantigen (SAg). In this report we showed that a high frequency of NOD Vbeta3(+) T cells that escape deletion are activated in vivo and that this phenotype is linked to the Mtv-3 locus. One potential mechanism of SAg presentation to peripheral T cells is by activated B cells. Consistent with this idea, we found that NOD mice harbor a significantly higher frequency of activated B cells than nondiabetes-prone strains. These activated NOD B cells expressed cell surface molecules consistent with APC function. At the molecular level, the IgH repertoire of activated B cells in NOD mice was equivalent to resting B cells, suggesting a polyclonal response in vivo. Genetic analysis of the activated B cell phenotype showed linkage to Idd1, the NOD MHC haplotype (H-2(g7)). Finally, Vbeta3(+) thymocyte deletion and peripheral T cell activation did not require B cells, suggesting that other APC populations are sufficient to generate both Mtv-3-linked phenotypes. These data provide insight into the genetic regulation of NOD autoreactive lymphocyte activation that may contribute to failure of peripheral tolerance and the pathogenesis of type I diabetes.     

Isotypes of spontaneous and mitogen-induced autoantibodies in SLE-prone mice

A common cellular abnormality of all murine strains prone to systemic lupus erythematosus (SLE) is an increased spontaneous polyclonal expansion of B cells. Our findings support the existence of this SLE-associated abnormality because the numbers of B lymphocytes secreting all the different IgG subclasses and IgM in spleens of all lupus-prone mice are elevated, compared to levels of normal splenic immunoglobulin-producing cells. We also report that 1) spontaneous polyclonal stimulation of immunoglobulin in autoimmune mice is preferential for subclass, and that the preferentially stimulated isotypes in each SLE strain consistently dominate both circulating and kidney-deposited immune complexes; 2) distinct patterns of isotype preference exist among the autoimmune strains determined by inherent B cell proliferative abnormalities or by B cell proliferation affected by thymus-derived lymphocytes; and 3) chronic administration of the TI B cell mitogen Lipid A in late-life SLE-prone mice induces an early-life glomerulonephritis with auto-antibodies of an isotype composition characteristic of those spontaneously produced by inherently abnormal B cells of early-life lupus mice.     

T cell regulation of immunoglobulin class expression in the B cell response to TNP-Ficoll: characterization of the T cell responsible for preferential enhancement of the IgG2a response

Syngeneic T cells injected into athymic nu/nu mice cause a preferential enhancement in the amount of IgG2a anti-TNP Ab produced by these mice to TNP-Ficoll. This enhancement appears to be caused by T cell effects on the IgG switching pathway. Through the use of F1----parent chimeras, the helper T cells were shown to affect TNP-Ficoll-responsive B cells in an H-2-unrestricted manner. The ability of T cells to mediate this IgG2a enhancement did not appear to be unique to any particular murine genetic background, because it was observed with T cells and nu/nu mice of C57BL/10, BALB/c, CBA/Ca, and B10.D2 strains. Priming of T cell donors with Ficoll or TNP-Ficoll did not increase the ability of splenic T cells, on a per cell basis, to enhance the IgG2a Ab response to TNP-Ficoll. The T cell population responsible for modulating the isotypic response was found to be sensitive to C-mediated cytotoxicity with both anti-Lyt-2 and anti-Lyt-1 hybridoma Ab. Although T cells from both the thymus and the spleen expressed enhancing activity, splenic T cells were more effective, on a per cell basis, than were thymocytes. The observations suggest that T cells that appear to enhance the switch to IgG2a in TNP-Ficoll-responsive B cells are not effectively primed by the antigen and interact with TNP-Ficoll-activated B cells through an H-2-unrestricted mechanism.     

Igh-C allotype-linked control of anti-DNA production and clonotype expression in mice infected with Plasmodium yoelii

The infection of nonlethal strain of Plasmodium yoelii induces the formation of IgG anti-DNA antibodies as a result of polyclonal B cell activation. By using various nonautoimmune strains of mice including H-2 or Igh congenic or recombinant mice, the levels and clonotypes of anti-DNA antibodies elicited by the malaria infection were analyzed in relation to the expression of the MHC or Igh gene. Our results showed there were little, if any, differences in serum anti-DNA levels and their clonotypes among B10 and B6 H-2 congenic mice. In contrast, malaria-induced IgG anti-DNA responses markedly differed quantitatively and clonotypically between murine strains bearing the Ighb allotype and those bearing the Igha, Ighj, Ighd, or Ighn allotype. The latter group of mice produced approximately 5 to 10 times more IgG anti-DNA antibodies than the former group of mice. Clonotypically, mice bearing the Ighb allotype developed high alkaline anti-DNA antibodies of pH 8.0 to 8.5, whereas non-Ighb mice failed to express such alkaline anti-DNA spectrotypes, and exhibited more neutral spectrotypes (pH 7.0 to 8.0). Studies on the Igh recombinant mice indicated that the observed quantitative and clonotypical differences in IgG anti-DNA production was not associated with the variable region, but with the constant region of the Igh gene complex. Our results have suggested that IgG anti-DNA responses occurring as a result of polyclonal B cell activation during the course of malaria infection markedly differs quantitatively and clonotypically among murine strains and appear to be controlled at least in part by the Igh-C gene or gene(s) closely linked to it.     

Genetic control of susceptibility to experimental autoimmune uveoretinitis in the mouse model. Concomitant regulation by MHC and non-MHC genes.

Experimental autoimmune uveoretinitis (EAU) in animals is a T cell-mediated autoimmune response directed against cells of the neural retina, in particular the photoreceptors. EAU can be induced in susceptible strains of mice by immunization with purified retinal Ag, and serves as a model for human uveitis. Because strong HLA associations have been noted in a number of human uveitic diseases, we investigated the role of MHC vs non-MHC genes in the control of susceptibility to ocular autoimmunity using the mouse EAU model. Selected strains representing most of the known independent H-2 haplotypes, as well as several H-2-recombinant and congenic strains, were immunized with interphotoreceptor retinoid-binding protein. Ocular pathology was induced in strains of the H-2k haplotype and their I-A-matched congenics, as well as in strains of the H-2r, H-2b, and H-2d haplotypes. In a series of experiments utilizing intra-H-2 recombinant strains, MHC control of susceptibility was tentatively mapped to the I-A subregion of the H-2k. Expression of the I-Ek gene product was not required for susceptibility to EAU, and in fact appeared to have an ameliorating effect on disease. Incidence and severity of disease obtained in strains sharing the same H-2 on a different background, or sharing the same background in the context of a different H-2, indicated that non-MHC genes contribute significantly to the regulation of EAU. Disease expression of susceptible H-2 haplotypes was highest in strains with B10 background (permissive) and ranged from intermediate to absent in strains with other (nonpermissive) backgrounds. The data suggest that although the ability to develop ocular pathology is dependent on the I-A subregion of the H-2, the final expression of disease in susceptible haplotypes is largely determined by background, non-MHC genes.     

Pertussis toxin prevents the induction of peripheral T cell anergy and enhances the T cell response to an encephalitogenic peptide of myelin basic protein.

In a murine model of T cell-mediated autoimmune disease, experimental autoimmune encephalitis (EAE), 80% of all encephalitogenic T cell clones in H-2u mice use the V beta 8.2 TCR element. To induce EAE in susceptible strains of mice either heat-killed Bordetella pertussis organisms or Bordetella pertussis toxin (PT) must be injected in addition to Ag in CFA. We investigated the mechanisms by which PT facilitates the induction of EAE. Our data show, that PT interferes with the induction of Ag-induced peripheral T cell anergy. Furthermore it has a specific adjuvanticity for the autoantigen pAc1-11 in vivo and acts as a selective mitogen in vitro. We also tested the hypothesis that PT is a bacterial superantigen that specifically expands the V beta 8.2+ subset of T cells, thereby expanding the encephalitogenic T cell clones that are contained in this subset, so that the number of autoreactive T cells is brought over a critical threshold, necessary to induce autoimmune disease. Our data show that PT is not a superantigen. Staphylococcal enterotoxin B, a V beta 8.2-specific superantigen, does not enhance the immune response to the encephalitogenic peptide.     

Antigen-specific lymphocyte proliferative responses in inbred mice after Trichinella spiralis infection.

The in vitro antigen-specific lymphoproliferative response of spleen, mesenteric lymph node (MLN), and coeliac lymph node (CLN) cells taken from various strains of inbred mice infected with Trichinella spiralis was assessed. In most experiments cell populations were stimulated with excretory/secretory antigens (ESA) derived from adult and larval worms. Lymphoid cells collected 5-7 days postinfection were usually the most responsive to ESA as measured by [3H]thymidine uptake. Spleen cells were more responsive than either MLN or CLN cells. There was a correlation between in vitro ESA stimulation and worm rejection in strong- and weak-responder strains of mice. Spleen and MLN cells of NFS mice showed higher antigen-specific responsiveness, whereas the same cells from B10.BR (H-2k) and B10.Q (H-2q) strains of mice were less responsive. Among intermediate responder strains 2 patterns were observed. Spleen and MLN cells of BuB and DBA/1 mice responded more strongly than those of C3H mice. Dose-response experiments demonstrated that increasing the infective dose of larvae to the host usually increased subsequent in vitro antigen-specific lymphoproliferation. Furthermore, non-MHC-linked genes appear to be the primary determinant of antigen-specific T-cell-proliferative responses in inbred mice infected with T. spiralis.     

Roles of I-E molecule and CD28 costimulation in induction of suppression by staphylococcal enterotoxin B in vivo.

Exposure to bacterial superantigens leads to the induction of a subsequent state of immune hyporesponsiveness. Using a transwell coculture system, a previous report demonstrated that splenocytes from staphylococcal enterotoxin B (SEB)-injected BALB/c mice secreted soluble mediators to suppress the proliferative response of naive syngeneic splenocytes to SEB stimulation. We show in the present study that, in contrast to the suppressive effect induced by SEB in BALB/c (H-2(d) haplotype), MRL(+/+), and MRL-lpr/lpr (H-2(k)) mice, SEB-primed splenocytes from I-E(-) strains such as B6, B10, A.BY (H-2(b)), and A.SW (H-2(s)) mice failed to inhibit the CD25 expression and the proliferative activity of their syngeneic naive responder splenocytes. Further results revealed that the SEB-primed cells from BALB/c, but not B6, mice inhibited the CD25 expression and proliferation of naive responder cells from either BALB/c or B6 mice, indicating the critical regulatory role of the effector cells. Unlike SEB, staphylococcal enterotoxin A induced profound suppression in both BALB/c and B6 mice. Moreover, the suppressive competence of SEB-primed splenocytes was diminished in CD28-deficient BALB/c mice. Taken together, our results indicate that when SEB is used as a stimulator in vivo, both the I-E molecule and CD28 costimulation are required for the induction of regulatory cells bearing suppressive activity.     

Autoimmune syndrome after induction of neonatal tolerance to alloantigens: effects of in vivo treatment with anti-T cell subset monoclonal antibodies

BALB/c (H-2d) mice rendered tolerant to h-2b alloantigens by neonatal injection of semiallogeneic (C57BL/6 X BALB/c)F1 spleen cells develop autoimmune features due to an abnormal activation of persisting F1 donor B cells. The role of T cells in this autoimmune syndrome was studied by in vivo treatment of tolerant mice with anti-L3T4(GK-1.5) or anti-Ly-2 (H-35-17.2) monoclonal antibodies. The treatment of tolerant mice from day 2 to day 21 of life with anti-L3T4 MAb completely prevented the occurrence of circulating immune complexes of anti-ssDNA anti-Sm and anti-hapten (FITC) IgG antibodies as well as the glomerular deposition of Ig that were usually seen in untreated tolerant mice. This effect persisted for at least 6 wk after stopping this treatment. When the injections of anti-L3T4 MAb were delayed until day 15 of life, a very significant decrease of the autoimmune manifestations was still observed. Treatment of tolerant mice with anti-Ly-2 MAb during the same period had no effects on the autoimmune disease as compared with untreated tolerant mice. No effects on the maintenance of tolerance vs H-2b alloantigens were observed after treatment with anti-L3T4 MAb, as followed by the decrease of CTL and CTL-p alloreactivity and by the persistence of F1 donor B cells, indicated by the presence of Ig bearing the Ighb donor allotype. These results suggest the existence of interactions between L3T4+ T cells and persisting autoreactive B cells from F1 donor origin in the development of the autoimmune syndrome after neonatal induction of transplantation tolerance.     

Leishmania donovani infection in heterozygous and recombinant H-2 haplotype mice

On a B10 (Lshs) genetic background the development of acquired T-cell-mediated immunity to Leishmania donovani infection in mice is under H-2-linked genetic control. Three phenotypic patterns of recovery were previously observed: "early cure" (H-2s, H-2r), "cure" (H-2b) and "noncure" (H-2d, H-2q, H-2f), with cure behaving as a recessive trait in H-2b/H-2d mice. In this study the long-term response to L. donovani is followed over 130 days of infection in eight recombinant haplotype strains and in six further heterozygous haplotype combinations. Noncure in B10.HTG mice, which carry d alleles for loci at the K end and b alleles for loci at the D end of H-2, confirms that H-2-linked genetic control of the acquired response to L. donovani infection is located in the K end. The complex pattern of dominance relationships observed in the additional heterozygous haplotypes studied, the variable phenotypic response of H-2k mice and of recombinant haplotype strains carrying IEk in common, and the differential early curing activity observed in heterozygotes involving the s but not the r early cure haplotype and in recombinant haplotype mice carrying s alleles to the left of IE suggest, however, that more than one subregion (IE and presumably IA) are involved. Results are interpreted in the light of immunoregulatory T-cell populations previously demonstrated in noncure, cure, and early cure strains.     

The immune response in aged C57BL/6 mice. I. Assessment of lesions in the B-cell and T-cell compartments of aged mice utilizing the Fc fragment-mediated polyclonal antibody response

The Fc fragment-mediated polyclonal antibody response was utilized to assess B-cell, T-cell, and macrophage reactivity in aged C57BL/6 mice. Spleen cells from aged (28–30 months) mice were found to be deficient in their capacity to proliferate and produce polyclonal antibody in response to Fc fragments when compared to adult (2–3 months) controls. Since T cells are required for the Fc-induced polyclonal antibody response, T cells from aged mice were assessed for their ability to restore the polyclonal antibody response in T-cell-depleted adult spleen cell populations. Aged T cells were not as effective as adult T cells in restoring the antibody response. The T-cell requirement in the Fc-induced polyclonal response has been shown to be replaceable by the Fc-stimulated T-cell replacing factor (Fc)TRF. T cells derived from aged mice were unable to produce (Fc)TRF to the level of adult cells. In addition to a defect in the T-cell compartment a lesion exists in the B-cell compartment of aged mice as well. Adult T cells were not capable of restoring the polyclonal antibody response of aged B cells any higher than aged T cells indicating a B-cell defect. Moreover, when a direct B-cell activator, Fc subfragment, was employed, the aged B cells were not stimulated to the level of adult controls. To test the ability of aged macrophages to function as accessory cells in the polyclonal response, macrophage-depleted adult spleen cells were mixed with aged or adult macrophages and the response measured. The results indicate that aged macrophages restore the polyclonal antibody response as efficiently as their adult counterpart.     

Inhibition of macrophage accessory cell function in casein-treated B6C3F1 mice

Humoral immunity of casein-treated B6C3F1 mice was evaluated. Splenocytes from casein-treated mice sensitized in vitro exhibited a marked suppression in their antibody response to the T-dependent antigen, SRBC (82%) and T-independent antigen, DNP-Ficoll (80%). In contrast, a control response to the polyclonal antigen, lipopolysaccharide (LPS), was observed. Cell fractionation and crossover reconstitution assays of adherent (ADH) and nonadherent (NAD) splenocyte populations from vehicle and casein-treated mice indicated that: 1) ADH splenocytes from casein-treated mice were responsible for suppression of humoral responses, 2) NAD splenocytes from casein-treated mice reconstituted with vehicle or naive ADH cells abrogated the immunosuppression, and 3) suppression of humoral responses in cultures containing casein ADH splenocytes was due to this cell populations inability to function as accessory cells in humoral responses rather than induction of suppressor macrophages. Results from in vivo studies with casein-treated mice sensitized with sheep red blood cells or dinitrophenyl-Ficoll paralleled the in vitro results.