Role of T cells in regulating expression of the B cell repertoire. Anti-ssDNA precursor frequency of DBA/2 B cells is increased in the presence of T cells from NZB mice

Splenic B cells from DBA/2 and NZB mice were compared with regard to precursor frequency of anti-ssDNA-producing cells. Using a modification of the splenic fragment assay, we show that NZB T cells are capable of increasing the frequency of expression of anti-ssDNA precursors in DBA/2 splenic B cells. When limiting numbers of splenic B cells of DBA/2 origin were adoptively transferred into an irradiated (1200 rad) recipient, the co-transfer of NZB T cells markedly increased the frequency of anti-ssDNA precursors in cultured splenic fragments. The anti-ssDNA produced under these conditions was exclusively IgM and exhibited a high degree of cross-reactivity with TNP and fluorescein. Thus, the increase in anti-ssDNA precursor frequency reflected an expansion of the B cell repertoire to include precursors of polyspecific antibody-producing cells that under normal circumstances are not expressed. The ability of NZB T cells to increase the anti-ssDNA precursor frequency was further defined by the CBA/N immunodeficiency gene xid, in that B cells from DBA/2.xid donors did not exhibit increased anti-ssDNA precursor frequency in the presence of NZB T cells. When NZB splenic B cells were co-transferred with DBA/2 T cells, the anti-DNA precursor frequency of the NZB B cells was not reduced. This study demonstrates that T cells can influence the emergency of B cell clones in an Ag-nonspecific manner. The well documented in vivo spontaneous polyclonal activation of NZB B cells may be secondary to T cell-mediated expansion of the B cell repertoire.     

In vivo effects of hyperdiploid Ly-1+ B cells of NZB origin

Cells with increased chromosome number and DNA content have been found in the spleens of old NZB mice. These hyperdiploid cells are of clonal origin and demonstrate discrete IgH chain gene rearrangements by Southern blot analysis. In this report, hyperdiploid cells were analyzed by three-color flow cytometric techniques and found to be Ly-1+ B cells which were dull for Ly-1 and bright for surface IgM. These cells, unlike typical diploid Ly-1+ B cells, were negative for B220/6B2 and surface IgD. Hyperdiploid Ly-1+ B cells were found to be the predominant splenic subpopulation in animals receiving a spleen cell transfer from donors which possessed hyperdiploid Ly-1+ B cells. (NZB x DBA/2)F1 recipients of NZB spleen cells demonstrated a 10- to 1000-fold increase in Ly-1+ B cells in the spleen but showed no increased levels of Ly-1+ B cells in the peritoneum. Nearly all the splenic Ly-1+ B cells were hyperdiploid with the phenotype of the NZB parent. Cytogenetic analysis revealed that all the hyperdiploid cells were NZB donor cells. These findings suggest that the increase in splenic Ly-1+ B cells in the F1 recipients was due to expansion of injected splenic hyperdiploid Ly-1+ B cells of NZB origin. All of the F1 recipients of NZB hyperdiploid Ly-1+ B cells demonstrated a significant decrease in endogenous B cells as well as decreased serum IgM and anti-ssDNA autoantibodies. These studies suggest that hyperdiploid Ly-1+ B cells are different from typical peritoneal Ly-1+ B cells both in the lymphoid organs to which they home and in their proliferative capacity. NZB hyperdiploid Ly-1+ B cells, which may arise as a natural consequence of hyperactive Ly-1+ B cells, may play an immunoregulatory role in the spleen.     

Comparison of response to stem cell differentiation signals between normal and autoimmune mouse strains

Normal DBA/2 and autoimmune NZB mice were studied with regard to signals eliciting differentiation and division of bone marrow stem cells. Irradiated (NZB X DBA/2)F1 mice were repopulated with various combinations of T-depleted bone marrow from NZB and DBA/2 mice. In response to the repopulation signal of irradiation, recipients of autoimmune NZB marrow initially demonstrated expansion of LY-5+ lymphoid and hemopoietic cells, particularly of the B cell lineage. The greater the proportion of NZB marrow, the higher the percentage of lymphoid cells observed 2 wk post-repopulation. B cells (ThB-positive cells) were increased in disproportionate numbers in recipients of NZB marrow, even those that had received as little as 20% NZB bone marrow cells. However, by 2 mo, the initially observed increase in lymphoid cells in recipients of NZB marrow was no longer observed. Up to 6 mo post-repopulation, cytogenetic analysis revealed that irradiated recipients were repopulated in the same proportion of DBA/2: NZB as was in the injected marrow. Endogenous colony formation assays indicated that recipients of 100% NZB, 80% NZB, and 20% NZB marrow all had greater numbers of splenic endogenous colonies than did recipients of DBA/2 marrow alone. These studies indicated that autoimmune NZB marrow repopulated irradiated mice in the proportion in which it was injected, but there was a disproportionate early increase in cells of the B lineage as well as a disproportionate increase in splenic colony formation.     

Studies on the influence of the internal environment on autoantibody production by B cells

Purified splenic B cells from autoimmune NZB and nonautoimmune DBA/2 mice were transferred to unmanipulated H-2 compatible xid recipients. The number of autoantibody-secreting clones present in recipient mice was quantitated at varying times after transfer using a splenic fragment assay. We found that NZB and DBA/2 B cells expanded equally well in equivalent xid environments. Cells from either donor expanded significantly better in autoimmune-prone NZB.xid as compared with DBA/2.xid recipients. Moreover, clones producing antibodies reactive with T cell surface antigens, bromelain-treated mouse red cells, or DNA expanded more rapidly than did cells producing antibodies to the nonautoantigen TNP-KLH. Serum autoantibody levels rose in concert with the increased numbers of autoantibody-producing lymphocytes. We conclude that factors present in the internal milieu of autoimmune-prone NZB.xid mice, rather than an intrinsic B cell defect, facilitate the expansion of (auto)antibody-secreting B cells.     

Similar in vivo expansion of B cells from normal DBA/2 and autoimmune NZB mice in xid recipients

B cells from normal DBA/2 and autoimmune NZB mice were transferred into H-2-compatible xid recipients where they engrafted without irradiation or other manipulation of the host. The properties of these cells and their interaction with the host environment were analyzed at the single cell level with a splenic focus assay. When similar numbers of NZB and DBA/2 anti-DNA-producing B cell precursors were transferred, they expanded at similar rates in xid recipients. The rate of expansion varied with the strain of the recipient: it was fastest in autoimmune-prone NZB . xid and slowest in DBA/2 . xid hosts. Cells producing antibodies reactive with the autoantigen DNA proliferated substantially faster than those reactive with the non-autoantigen trinitrophenylated keyhole limpet hemocyanin. These results suggest that 1) B cells from NZB mice do not behave differently from DBA/2 B cells, 2) the internal milieu of the recipient into which the cells are transferred has an important effect on B cell proliferation, and 3) B cells capable of autoantibody production may have a selective growth and/or differentiation advantage relative to other B cells.     

Evidence for a B lymphocyte defect underlying the anti-X anti-erythrocyte autoantibody response of NZB mice.

The autoimmune hemolytic anemia of NZB mice is pathogenetically mediated by a genetically prescribed anti-erythrocyte autoantibody response directed to the X erythrocyte autoantigen. The cellular locus of the immunoregulatory defect underlying the anti-X response was explored by adoptively transferring bone marrow cells (BMC) from NZB mice to lethally irradiated histocompatible recipients. Before adoptive transfer, BMC from donor mice were assayed for antigen-binding lymphocytes with receptors for the X autoantigen (X-ABL) by immunocytoadherence assays and for anti-X autoantibody-secreting cells (X-PFC) by plaque-forming cell assays. Twelve weeks after adoptive transfer, splenic lymphocytes from recipient mice were assayed for X-PFC and humoral anti-X autoantibody by Coombs' tests. Transfer of 15 to 30 x 10(6) BMC containing 6 to 12 x 10(3) X-ABL but no X-PFC from 6- to 8-week-old NZB mice to lethally irradiated BALB/c, B10.D2, C57BL/Ks, and DBA/2 mice produced X-PFC in 70% of the recipients. Development of X-PFC was not simply dependent upon available X-ABL since transfer of 15-30 x 10(6) BMC, containing comparable numbers of X-ABL, from BALB/c, B10.D2, C57BL/Ks, or DBA/2 mice to NZB or syngeneic recipients did not produce X-PFC. Transfer of BMC from NZB mice to BALB/c, B10.D2, and DBA/2 mice with weekly administrations of AKR anti-theta antiserum had no effect on the development of X-PFC; Tlymphocyte ablation was evidenced by the absence of theta+ spleen cells. These results suggest that the pathogenetic anti-X response is not genetically prescribed at the level of macrophages, humoral factors, or T cells, but rather appears to be a phenotypic expression of a primary B lymphocyte defect permitting or promoting differentiation of NZB X-ABL.     

Failure of NZB spleen to respond to prethymic bone marrow suppressor cells.

Mouse bone marrow contains theta-negative lymphocytes that can suppress an in vitro plaque response by spleen cells primed in vivo with burro red blood cells (BRBC). These bone marrow cells are radiosensitive and can be induced with thymosin fraction 5 or alpha 1 thymic peptides to express the theta antigen. Enrichment for these suppressor pre-T lymphocytes can be achieved by a one-step density centrifugation, macrophage depletion, or a combination of both procedures. NZB mice, which spontaneously develop an autoimmune disorder, have a suppressor abnormality revealed by this assay system. Upon analysis, they have normal BM pre-T suppressor cells but their spleen cells are refractory to the BM suppressor signal. NZB BM suppressor cells inhibit the response by DBA/2 spleen cells, but DBA/2 BM suppressor cells do not inhibit NZB spleen. This resistance to suppression is a property of the B cell fraction recovered from NZB spleen.     

Analysis of T cell and B cell function in Peyer's patch and lamina propria of New Zealand Black and DBA/2 mice

We have analyzed gastrointestinal immune function in both DBA/2 and spontaneously autoimmune New Zealand Black (NZB) mice. We have studied both in vitro proliferation and differentiation of Peyer's patch cells and have measured immunoglobulin (Ig) secretion by cultured jejunal segments. Peyer's patch B cells and T cells from both DBA/2 and NZB mice showed similar proliferative responses to Con A and lipopolysaccharide (LPS), respectively. Unlike NZB splenic B cells, isolated Peyer's patch B cells from NZB mice did not spontaneously secrete Ig of any isotype. Seven-day cultures of equal numbers of Peyer's patch T cells and B cells resulted in similar patterns of secretion of IgA, IgG, and IgM in both strains. The addition of Con A to cultures of DBA/2 Peyer's patch cells consistently resulted in a onefold to threefold increase in IgA secretion after 7 days. Con A stimulation of NZB Peyer's patch cells did not produce any increment in IgA secretion. LPS stimulation of Peyer's patch cells from either strain resulted in a similar increase in IgG secretion with little effect on IgA secretion. The in vivo correlate of this finding was seen in the IgA to IgG ratio of Ig secreted by cultured jejunal fragments. In DBA/2 mice the rates of IgA/IgG varied from 2.36 to 4.85, whereas in NZB mice the ratio never exceeded 0.5. These experiments show that defects on the T cell compartment of NZB mice encompass gut-associated lymphoid tissue. The possible relationship of these findings and previously observed defects in oral tolerance is discussed.     

Studies of bone marrow progenitor cells in lupus-prone mice. I. NZB marrow cells demonstrate increased growth in Whitlock-Witte culture and increased splenic colony-forming unit activity in the Thy-1-, lineage- population.

Previous studies have demonstrated that NZB marrow can transfer features of autoimmunity. Therefore, we undertook a study of NZB marrow to determine whether it demonstrated any phenotypic abnormalities. In Whitlock-Witte cultures, NZB marrow cells generated nonadherent cells at low seeding densities, densities at which marrow from other strains did not generate nonadherent cells. In contrast, NZB marrow grew less well than controls in Dexter cultures. Inasmuch as the latter favor growth of granulocyte-macrophage precursors and the former B cells, these results suggest a possible skewing of NZB marrow cells toward lymphocyte production. Unfractionated marrow cells from NZB mice were found to produce 10-fold more splenic colonies in lethally irradiated recipients than marrow cells from control mice. This result was independent of the genotype of the recipient. When the progenitor Thy-1lo, Lin- marrow subpopulation was studied, NZB mice did not differ substantially from controls regarding splenic CFU. Therefore, Thy-1-, Lin- marrow cells were studied as a possible source of the excess splenic CFU in NZB mice. Indeed, the NZB Thy-1-, Lin- population contained 30-fold more splenic CFU than did the Thy-1-, Lin- population from control mice. These results suggest that NZB mice have unusual marrow progenitor cells; such cells may play a role in their autoimmune disease.     

Immunologic abnormality in NZB/NZW F1 mice. Thymus-independent occurrence of B cell abnormality and requirement for T cells in the development of autoimmune disease, as evidenced by an analysis of the athymic nude individuals

Both NZB nu/+ and NZW nu/+ mice were microbially clean by cesarean section. The (NZB x NZW)F1 hybrid (NZB/W) nu/nu mice and nu/+ littermates were then generated by mating of NZB nu/+ with NZW nu/+mice under specific pathogen-free conditions. The female NZB/W F1 nu/nu mice did not develop autoimmune kidney disease, whereas all of nu/+ female littermates mice exhibited proteinuria and died of renal failure with a 50% survival time of 35 wk. Namely, nude mice had no signs of proteinuria up to the time of their death caused by other diseases rather than glomerulonephritis, and their mean survival time was greater than 45 wk. Nude mice had also no anti-ssDNA antibody in their serum. However, splenic B cells of NZB/W nude mice exhibited hyper-responsiveness to both LPS and B151-TRF2, a T cell-derived polyclonal B cell-stimulation factor, and produced large numbers of Ig-secreting cells and anti-TNP plaque-forming cells as well as anti-ssDNA antibody comparable to the nu/+ littermate mice. Interestingly, thymus-engrafted NZB/W nude mice developed autoimmune disease exemplified by the induction of anti-ssDNA antibody and proteinuria at approximately the same time as their nu/+ littermates. These results indicate that the B cell hyper-responsiveness found in NZB/W mice is apparently determined by the T cell-independent process, and T cells are obligatorily required for the development of autoimmune disease in NZB/W mice.     

Transfer of long-lasting tumor immunity by immune T cells from MHC congenic mice: Migration,survival and tumor-protectivity of cytotoxic donor cells

Immunocompetent B10.D2 (H-2^d) mice are able to reject the highly malignant lymphoma ESb of DBA/2 (H-2^d) origin very effectively. Seven days after intravenous injection of the ESb tumor cells, B10.D2 mice developed a strong tumor-rejection response which was associated with the generation of anti-tumor T cells in their spleens with direct cytotoxic activity. Most of the cytotoxic potential was directed against the minor histocompatibility differences as demonstrated by the lysis of unrelated DBA/2 derived Eb tumor cells and normal DBA/2 but no B10.D2 derived ConA lymphoblasts. A previously performed clonal analysis, however, revealed a minority population of CTL clones which specifically recognized the ESb specific transplantation antigen (ESb-TATA). When transferred systemically into DBA/2 mice, the B10.D2 anti-ESb immune spleen cells could delay the outgrowth of s.c. transplanted ESb tumor cells. When the ESb tumor cells were experimentally distributed in a s.c. implanted sponge-matrix, the i.v. injected B10.D2 immune cells could confer complete protective immunity against the metastatic tumor, provided the recipients were pre-treated with 5 Gy to allow a better take of the allogeneic cells. The distribution of intravenously injected B 10D2 donor spleen cells was assessed in the recipients up to 50 days by cytotoxicity testing and assaying for the expression of the ₂ microglobulin allelic form b ( ₂m^b). These tests revealed a high propensity of donor cells to populate the spleen and lymph nodes of the DBA/2 recipients. Again this was particularly marked in sublethally irradiated mice where a long-lasting lymphoid chimerism was established.     

Autoimmune CD4+ T cells interfere with immune tolerance to a thymic-independent antigen

The ability of autoimmune T cell subsets to interfere with tolerization of B cells can be studied by using thymic-independent Ag. We have defined an abnormality within the CD4+ T cell compartment in young NZB and MRL-lpr/lpr mice by studying tolerance of spleen and B cells to the thymic independent Ag, fluorescein-Brucella abortus. Tolerization of spleen cells is defective in MRL-lpr/lpr mice, but not MRL-+/+ or C3H.lpr mice, suggesting that the defect requires both the autosomal MRL background and the lpr gene to be present. T enriched cells from NZB mice and from MRL-lpr/lpr mice (but not MRL-+/+ or C3H.lpr mice) reverse tolerance in spleen cells from [NZB X DBA/2]F1 and C3H/HeJ mice, respectively. This interference is removed by treatment with anti-CD4 antibody and C. Supernatants from cultured T cells of NZB and MRL-lpr/lpr mice also prevent tolerance in spleen cells of [NZB X DBA/2]F1 and MRL-+/+ mice, respectively, unless CD4+ cells are removed prior to T cell culture. Removal of T cells from NZB and MRL-lpr/lpr spleen cells allows normal tolerization of B cells, which is abrogated by the addition of syngeneic T cells or cultured T cell supernatants. This effect also depends on the presence of CD4+ T cells. These studies show that in MRL-lpr/lpr mice, through interaction of the lpr and MRL background genes in a T cell subset, and in NZB mice, CD4+ T cells interfere with B cell tolerance to a thymic-independent Ag.     

Regulation of antigen induced changes in cyclic nucleotide levels in NZB/wf1 mice.

Normal C57BL/6J mice respond to the iv injection of antigen with an increase in splenic cAMP at 2 min. NZB/WF₁ mice are predisposed to autoimmune and immunological disorders upon aging. The ability of NZB/WF₁ mice to respond to antigen with an increase in their splenic cAMP level was found to diminish with age. This loss of responsiveness is antigen specific and not due to a loss of adenylate cyclase activity in spleen cells of old NZB/WF₁ mice. The adoptive transfer of spleen cells from unresponsive old mice into responder young mice inhibited the cAMP response to antigen by the recipients. Spleen cells from young responsive mice, on transfer into old nonresponsive NZB/WF₁ recipients, resulted in restoration of the cAMP response to antigen. In both cases, the activity of donor cells was dependent on the transfer of T cells. These results indicate that populations of T cells participate in the regulation of the cAMP response to antigen by NZB/WF₁ mice. The response of old mice could also be restored by treatment with indomethacin, and also the spleen cells of such treated donors failed to suppress the cAMP response of young recipients. Together, the results suggest a role for prostaglandins in regulating the cAMP response to antigen.     

Proliferation of anti-DNA-producing NZB B cells in a non-autoimmune environment

This study demonstrates that purified NZB B cells, but not other NZB spleen cell populations, are capable of transferring anti-DNA antibody production into unirradiated H-2-compatible xid recipients. The number of autoantibody-producing B cells and the concentration of anti-DNA antibody found in the recipients correlated directly with the number of NZB B cells transferred. In addition, the number of anti-DNA-secreting lymphocytes found in the xid hosts increased exponentially with time post cell transfer. Several lines of evidence suggest that this phenomenon reflected the rapid proliferation of donor NZB B cells in the xid environment. Significantly, such proliferation was characteristic of donor cells that produced autoantibodies, but not of splenic B cells as a whole. These results suggest that stimulated NZB B cells can both induce and perpetuate autoantibody production in a normally non-autoimmune environment and in the absence of autoimmune helper cells.     

Defective B cell tolerance induction in New Zealand black mice. I. Macrophage independence and comparison with other autoimmune strains

B cell unresponsiveness was examined in vitro by using spleen cells from autoimmune NZB, BXSB/Mp male, MRL/Mp-Ipr/Ipr (MRL/l), and control mice, and the tolerogen trinitrophenyl human gamma-globulin (TNP-HGG). The B cell subset responsive to TNP-Brucella abortus in each autoimmune and control strain that was tested was highly susceptible to tolerance induction with the use of high epitope density conjugates (TNP30HGG and TNP32HGG). When a tolerogen with a lower epitope density was used (TNP7HGG), several control strains were all rendered tolerant in a thymic-independent and hapten-specific manner. NZB B cells were resistant to all concentrations of TNP7HGG tested, whereas B cells from BXSB/Mp male and MRL/1 mice were resistant to low concentrations of this tolerogen. NZB mice were resistant in addition to tolerance induction with TNP9HGG, TNP10HGG, and TNP12.7HGG. Experiments were performed to determine whether splenic macrophages played a role in resistance to tolerance in NZB mice. The mixing of NZB and control DBA/2J T cell-depleted splenocytes revealed no modulatory effects by the accessory cells in culture. Moreover, B cells rigorously depleted of macrophages by double Sephadex G-10 column passage exhibited characteristic patterns of resistance or susceptibility in NZB and control strains, respectively. These findings support the conclusion that resistance to tolerance in NZB mice is determined at the B cell level and are consistent with the hypothesis that diverse immunoregulatory disturbances contribute in varying degrees to the development of systemic lupus erythematosus in different inbred strains of mice.     

20 alpha hydroxysteroid dehydrogenase (20 alpha SDH) activity in New Zealand mice T lymphocytes and bone marrow cells: effect of age, sex, and castration.

The activity of 20 alpha hydroxysteroid dehydrogenase (20 alpha SDH), a T lymphocyte-associated enzyme, was measured in fetal liver, thymus, spleen, and bone marrow cells from NZB, NZW, and (NZB X NZW)F1 (B/W) mice. There was an age-dependent increase of 20 alpha SDH activity in bone marrow cells, and a decrease in thymocytes and splenic T lymphocytes. Treatment with anti-theta and complement did not reduce the 20 alpha SDH activity of bone marrow and fetal liver cells, but reduced the activity of spleen cells. PHA stimulates both 20 alpha SDH activity and thymidine incorporation in splenic, bone marrow, and fetal liver lymphocytes. The results suggest that the enzyme in the bone marrow and fetal liver is located in pre-T lymphocytes. Enzymatic activity in bone marrow cells taken from female B/W mice (older than 7 months) was 40 to 20% lower than in male mice. Orchidectomy, but not ovariectomy, caused a significant decrease in thymocyte 20 alpha SDH activity. Orchidectomy depressed and ovariectomy enhanced 20 alpha SDH activity of bone marrow cells. The 20 alpha SDH activity of fetal liver cells from B/W mice was twice as high as in either parent strain. No 20 alpha SDH activity was found in fetal liver cells taken from BALB/C SJL or C57BL/6 mice. A model is proposed to explain the age- and sex-related changes in 20 alpha SDH activity of pre-T and T lymphocytes in healthy and pathologic conditions.     

Thymic hormone modulation of age-induced changes in the induction of graft-versus-host disease by DBA/2J lymphocytes

Aging induces a number of changes in the immune system, including the involution of the thymus which results in the loss of thymic hormone production and alteration in T cell function. One age-dependent change in immune response is the increasing risk of developing acute or chronic form of graft-versus-host disease (GVHD) following bone marrow transplantation as the age of the recipient increases. A murine model of GVHD that has been extensively studied is one in which injection of C57BL/6 spleen cells into unirradiated B6D2F1 mice results in an acute form of GVHD characterized by cytolytic T lymphocytes (CTL), suppressor cells, runting, and occasionally death. In contrast, injection of DBA/2J spleen cells results in a chronic form of GVHD characterized by a lack of CTL and hyperproduction of immunoglobulin and autoantibodies. This study shows that the GVHD response of DBA/2J spleen cells is dependent on the age of the donor DBA/2J mice. If spleen cells from DBA/2J mice older than 3 months are injected into B6D2F1 recipients, CTL and lack of immunoglobulin production indicative of acute GVHD result. Administration of thymosin fraction 5, a collection of thymic hormones, to DBA/2J mice older than 3 months caused spleen cells from these treated mice to give a GVHD response characteristic of the chronic form of GVHD in B6D2F1 recipients. Thus, thymic hormones were able to modulate the changes in GVHD responses of DBA/2 lymphocytes that occur as the mice age. Preliminary fractionation of TF5 has indicated that there are at least two active thymic peptides present in TF5.     

Autoreactive B cells in lupus-prone New Zealand black mice exhibit aberrant survival and proliferation in the presence of self-antigen in vivo

To identify defects in B cell tolerance that may contribute to the production of autoantibodies in New Zealand Black (NZB) mice, we crossed soluble hen egg white lysozyme (sHEL) and anti-HEL Ig transgenes (Ig Tg) onto the NZB background. In this study, we have examined one of the first checkpoints involved in maintenance of peripheral B cell tolerance, follicular exclusion and elimination of self-reactive B cells in the absence of T cell help. Freshly isolated anti-HEL Ig Tg B cells were labeled with CFSE, adoptively transferred into sHEL recipients, and the fate of self-reactive anti-HEL Ig Tg B cells was followed using flow cytometry and immunofluorescence microscopy. Although anti-HEL Ig Tg B cells from NZB mice are appropriately excluded from B cell follicles in NZB sHEL recipient mice, they demonstrate aberrant survival, proliferation, and generation of anti-HEL Ab-producing cells. This abnormal response results from an intrinsic defect in NZB B cells, requires the presence of CD4(+) T cells, and is facilitated by the splenic environment in NZB mice. Thus, NZB mice have immune defects that interact synergistically to allow autoreactive B cells to become activated despite the presence of tolerizing autoantigens.     

Genetic studies in NZB mice. II. Hyperdiploidy in the spleen of NZB mice and their hybrids.

The presence of hyperdiploidy was studied in New Zealand black (NZB) mice and the progeny of NZB X DBA/2 crosses and backcrosses. Hyperdiploidy was observed in the spleens of a majority of NZB mice but not in DBA/2 mice at 1 year of age. In crosses of NZB with the DBA/2 strain, hyperploidy was observed only in backcrosses to NZB. Hyperdiploidy appeared to be determined by a recessivley inherited trait and was not related to the presence of other immunological abnormalities, including splenomegaly, hypergammaglobulinemia, and spontaneous antibodies cytotoxic for T cells and reactive with single-stranded DNA. Abnormal cells were not present in Concanavalin A-stimulated 48-h spleen cultures. There was no difference in the in vitro sister chromatid exchange rate between the autoimmune NZB strain and the non-autoimmune DBA/2 strain. Identification of NZB chromosomes by banding analysis showed that chromosomes 15 and 17 were frequently present in more than two copies in hyperdiploid spleen cells. NZB chromsomes also had reduced C-banding in an autosomal pair. These studies indicate that chromosomal abnormalities which occur in NZB mice may be useful as genetic and cytogenetic markers.     

Peripheral (somatic) expansion of the murine cytotoxic T lymphocyte repertoire. II. Comparison of diversity in recognition repertoire of alloreactive T cells in spleen and thymus of young or aged DBA/2J mice transplanted with bone marrow cells from young or aged donors

Lethally irradiated (1000 R whole body) DBA/2J mice of 10 wk or 20 mo of age were repopulated with anti-Thy-1.2-treated DBA/2J bone marrow cells of 10-wk- or 20-mo-old donors. Sixty days post-transplant, limiting dilution cultures of the spleen and thymus cell population of individual mice (for each group) were examined to assess the within-group and between-group diversity in the anti-H-2Kb allo-recognition repertoire. Our data are consistent with a significant expansion of the CTLp repertoire taking place in the periphery, beyond the early appearing specificities present in the thymus. Moreover, comparison of the repertoires in young recipients of young or aged marrow, or in aged recipients of young or aged marrow, support the notion that there is a defect in the peripheral environment of aged mice that results in altered expansion of the thymic CTLp repertoire. In addition, there is an intrinsic difference in bone marrow precursor cells of CTLp in aged mice that is revealed only in an aged environment.