Suppressor cells and immunodeficiency in (NZB x NZW)F1 hybrid mice.

Old (15-20 month) male (NZB x NZW)F1 (B/W) mice have severely impaired spleen cell reactivity to phytohemagglutinin (PHA), a mitogen which stimulates mainly T lymphocytes. Spleen cells from old mice markedly suppressed the PHA response of splenocytes from young (3-4 month) B/W males. Similar suppressor activity was not present in the spleens of old mice of four nonautoimmune strains. The suppressor activity of old B/W spleen cells was mediated by a nonphagocytic, radioresistant, mononuclear leukocyte. Although this cell was eluted in the "T lymphocyte" fraction of nylon wool colums, it was not sensitive to treatment with anti-Thy-1 antiserum and complement. Suppressor activity was lost after 18 h incubation at 37 degrees C in tissue culture medium. Supernatants of these overnight cultures had no suppressive effect on fresh young B/W spleen cells. Old B/W spleen cells suppressed PHA reactivity more than concanavalin A or lipopolysaccharide reactivity. Kinetic studies demonstrated an increasing suppression with time over 72 h of culture. This study demonstrate that the severely impaired PHA reactivity of old B/W mice is mediated, at least in part, by active suppression.     

Regulatory T cells essential to prevent the loss of self-tolerance in murine models of erythrocyte-specific autoantibody responses

The spontaneous appearance of anti-erythrocyte autoantibodies resulting in autoimmune hemolytic anemia described in NZB mice more than 40?years ago provided a model for the study of mechanisms behind the loss of self-tolerance. We developed an in vitro model of this anti-MRBC response in which CD8(+) suppressor T cells were shown to be a controlling element. CD8(+) T cells from young NZB mice co-cultured with spleen cells from old, actively autoimmune NZB mice suppressed the anti-MRBC responses of the old mice. Eliminating the CD8(+) cells from young NZB spleen cells or even from non-autoimmune BALB/c spleen cells prior to culture removed the controlling influence of these CD8(+) cells and allowed the development of anti-MRBC-secreting cells. This review will consider the role of the CD8(+) suppressive cells in the anti-self-erythrocyte model in light of insights provided by current 'regulatory T cell' literature.     

Bone marrow cells from young and old New Zealand black mice can reconstitute B lymphocytes in severe combined immunodeficient recipients

The formation of B lymphocytes in young New Zealand Black (NZB) mice proceeds at an accelerated rate, resulting in a deficiency of B lineage progenitors in mice of 15 weeks of age and older. Multiple studies have indicated that intrinsic defects in B lineage cells as well as in the hemopoietic microenvironment in which they develop contribute to these cellular abnormalities. To determine whether the B-cell hyperactivity observed in young mice could be observed in a normal environment, bone marrow cells from young (4 weeks or less) NZB donors were transplanted into Severe Combined Immunodeficient (SCID) mice that have a marked deficiency of lymphocytes but an apparently normal hemopoietic microenvironment. Engraftment of donor lymphoid cells can occur without pretransplant conditioning regimens, thus minimizing the chances of transferring microenvironmental elements. Marrow from young NZB donors reconstituted surface IgM-expressing B cells and CFU-B (B-cell colony-forming unit) in the marrow of SCID mouse recipients to levels comparable to that observed with donor NZB.xid marrow. The latter mice carry the xid gene that ameliorates the defects exhibited by B lineage cells of NZB mice. Both the number of surface IgM-expressing B cells and CFU-B were higher in the spleen of SCID mice that received NZB grafts than marrow cells from donor BALB/c or NZB.xid mice. Marrow from young NZB donors also reconstituted Thy-1, L3T4 and Lyt2-expressing cells in the spleen to levels higher than observed with young NZB.xid donor cells. The transplantation of marrow from 6-month-old NZB donors made it possible to test whether B lineage cells were present in that tissue and could mediate reconstitution in the normal SCID environment. Marrow from old NZB donors did reconstitute B cells in the marrow and spleen of SCID recipients. The level of reconstitution was comparable to that mediated by young BALB/c cells and twice that of old NZB.xid donor cells. The absolute number of splenic CFU-B was also higher in recipients of old NZB marrow as compared to young BALB/c cells. Old NZB.xid donor marrow reconstituted splenic Thy-1, L3T4 and Lyt2 T cells to levels less than observed with NZB donor cells. Analysis of serum Ig in recipients of old NZB cells indicated higher levels of total IgM as compared to mice engrafted with NZB.xid cells, and anti-single stranded DNA antibodies were detected.     

Lymphocyte subpopulations in the thymus of NZB x NZW mice: phenotypic characterization by flow cytofluorometry analysis.

The composition of the thymocyte population was investigated as a function of age in the autoimmunity-prone NZB x NZW F1 (NZB x W) female mice and in control BALB/c female mice. Single- and two-colour flow cytofluorometry analyses were used to quantitate the cell surface binding of fluorochrome-conjugated antibodies directed against various lymphocyte markers and of fluoresceinated peanut agglutinin (PNA). In both mouse strains, two major phenotypically distinct thymocyte subpopulations were thus identified. The predominant subpopulation was characterized as bright Thy-1+, Lyt-1 + 2+ and bright PNA+, and the other one as dull Thy-1+, Lyt-1 + 2- and dull PNA+. The relative frequencies of these two subpopulations were similar in NZB x W and BALB/c mice at 3 months of age. However, from 6 months onwards, slight but significant differences became detectable between the two strains. Thus, in BALB/c mice, both thymocyte subpopulations regressed at approximately the same rate during ageing so that their relative proportions remained constant. In contrast, in NZB x W mice, while the number of bright Thy-1+ cells diminished as in BALB/c mice, the number of dull Thy-1+ cells barely varied from 3 to 12 months of age, which resulted in a proportional increase of this latter subpopulation. Moreover, elevated frequencies of surface immunoglobulin-bearing cells were recorded in the thymus of 8-12 month old NZB x W mice but not in BALB/c mice. Therefore, the development of autoimmunity in NZB x W mice appears associated with an abnormal age-dependent evolution of the intrathymic lymphocyte population.     

Studies on Lymphocyte Homing in Autoimmune Prone NZB Mice

Lymphocyte homing patterns in young (3-5 months old) and old (10-12 months old) autoimmune prone NZB mice were investigated by transferring ⁵¹Cr labelled lymphoid cells into syngeneic and H-2 compatible allogeneic recipients. We confirmed that non H-2 alloantigens as well as H-2 alloantigens can be important determinants of apparent abnormalities of cellular distribution with the techniques employed. No gross abnormalities of lymphocyte traffic were present in the young NZB mice as compared to the autoimmune resistant strains of mice when syngeneic cells are used. Spleen of older NZB mice appeared to be less attractive to lymph node cells than was the spleen from young NZB mice. Splenocytes of older NZB mice localized significantly more in the liver and less in the lymph nodes as compared with splenocytes from young NZB mice. The mechanisms underlying abnormalities of lymphoid cell distribution which feature the autoimmune-prone NZB mice are not yet clear and further studies will be necessary before they can be characterized definitively. Our findings, using syngeneic cells, are in disagreement with those of Zatz and Lance since evidence of abnormal distribution of lymphocytes in young NZB mice were not seen when syngeneic cells were employed.     

Abnormalities of third-order suppressor T cells in old (New Zealand black x New Zealand white) F1 mice.

The suppressor T cell (Ts) function of old NZW, NZB, C57BL/6 and (NZB X NZW) F1 [B/W)F1), mice to the 2,4-dinitro-1-fluorobenzene (DNFB) hapten was studied. Intravenous administration of dinitrophenyl (DNP) coupled syngeneic lymphoid cells (which normally induce DNP specific suppression) did not result in suppression of DNFB-specific contact hypersensitivity (CS) responses in old NZB or (B/W) F1 mice. Nevertheless, when spleen cells from these old mice were injected into young mice (either (B/W)F1 or A/Sn), strong suppression of the induction phase of CS responses was observed. In addition, effector phase suppressor activity was also observed when splenic cells from tolerized old (B/W) F1 donors were transferred into young (B/W)F1 mice during the effector phase of the CS response. In both cases, the significant cells in the transfer were I-J+ T cells. Thus, the old mice retained functional Ts1 and Ts2 suppressor cells. However, the suppressive activity of the old mice could be reconstituted with spleen cells from primed young mice, suggesting that they have a defect in the Ts3 subset. This was further supported by the finding that the significant cells from the primed young mice were I-J positive and cyclophosphamide-sensitive.     

In vitro studies on the phagocytosis of Staphylococcus aureus by peritoneal macrophages of New Zealand mice

The ability of peritoneal macrophages from NZB, NZW and BWF1 mice to phagocytose and subsequently kill Staphylococcus aureus has been studied and compared to peritoneal macrophages from CBA, BALB/c and C₃Hf mice. Phagocytic indices determined in young and old New Zealand mice did not differ from those of the control strains. The bactericidal activity of the peritoneal macrophages did not show any interstrain differences.

Incorporation of serum from old and young NZB mice into the culture medium did not affect phagocytosis or the rate at which phagocytosed bacteria were killed. Studies performed in the absence of serum from the culture medium showed that probably both phagocytosis and bactericidal activity were unimpaired.

     

Enhanced response of autoantibody-secreting B cells from young NZB/NZW mice to T-cell-derived differentiation signals

Spleen cells from young NZB/NZW mice spontaneously produce IgM antihistone and anti-DNA antibodies in culture, and this in vitro autoantibody production is T-cell dependent. In the present studies, we investigated the response of young autoantibody-producing NZB/NZW B cells to various T-cell-derived signals. Stimulation with unprimed allogeneic T cells resulted in a 10- to 20-fold increase in IgM antihistone and anti-DNA antibody production compared with cultures of B cells alone. The responding cells were found in the large B-cell fraction after separation on Percoll gradients. Allo-stimulated B cells from nonautoimmune mice produced much lower absolute amounts of IgM autoantibodies as well as total IgM compared with NZB/NZW cells. Marked IgM antinuclear antibody and total IgM production was also observed when NZB/NZW B cells were cultured with supernatants from TH2 but not TH1 T-helper clones. Although B cells from nonautoimmune mice produced high levels of autoantibodies after stimulation with lipopolysaccharide, only minimal levels were secreted in response to the active supernatants. These results suggest that young NZB/NZW mice have IgM autoantibody-producing B cells that are more sensitive to certain T-cell-derived signals compared with B cells from normal mice. Although these hyperresponsive NZB/NZW cells appear to be in an advanced stage of activation, they require additional T-cell signals to express this abnormality.     

Lack of synergy between T and B cells in the response to 2-mercaptoethanol in old NZB/W F1 mice

The responses of NZB × NZW (NZB/W) F₁ mice to 2-mercaptoethanol (2-ME) were examined from the viewpoint of T-B cell interaction. Young (1-mth-old) NZB/W F₁ mice responded to 2-ME in an almost similar pattern to that of BALB/c mice, although a slightly higher rate of DNA synthesis was observed in B cell-enriched cultures (75% B cells) containing 2-ME than in those of BALB/c mice. Old (9-mth-old) NZB/W F₁ mice showed an absent synergistic effect of T and B cells in the response to 2-ME. These results indicate an abnormality of T-B cell interaction particularly in old NZB/W F₁ mice.     

Comparison of T cell-mediated immune responsiveness of NZB, (NZB x &NZW)F1 hybrid and other murine strains.

The age-dependent capacity of NZB and (NZB x NZW)F1 hybrid, BALB/c, DBA/2, C57BL/6 and C3H mice to generate T cell-mediated immune responses was assessed qualitatively and quantitatively by measuring the following effector functions: (a) the time course of alloreactive cytotoxic T-cell activity triggered in vitro was comparable for NZ and other mouse strains; cell reactivity generated in vivo against EL4 tumour cells was low in young (NZB x NZW)F1 mice and in DBA/2 mice but was comparable for older (NZB x NZW)F1, NZB and other mouse strains; (b) the time-dependent, vaccinia virus-specific, cytotoxic T-cell activity after systemic infection was similar for all mouse strains; (c) the T cell-dependent primary footpad swelling after local injection with lymphocytic choriomeningitis virus was within the same range for all mouse strains tested with respect to size and kinetics of the reaction; (d) the cell-mediated immune protection against Listeria monocytogenes after systemic infection revealed that NZ mice are, independent of age, more susceptible than C3H or C57BL/6 mice and comparable to A strain mice. Therefore, these responses in young, or clinically relatively normal older, NZB or (NZB x NZW)F1 strains that are affected by a lupus-like autoimmune disease did not differ markedly from the range of responses of other mouse strains of 2-14 months of age, which are not known to be similarly diseased. Thus, overall cell-mediated immunity of NZ mice as assessed quantitatively and kinetically in these functional models is within normal ranges. Possible T-cell defects may therefore be selective and either do not occur or were not detected in these models.     

Immune suppression to nucleosides: differences between NZB and NZW mice

Previous studies (Y. Borel and M. C. Young, Proc. Natl. Acad. Sci. USA 1980. 77: 1593) have shown that one can raise nucleic acid-specific suppressor T cells which diminish either the T-dependent immune response in vivo or the T-independent immune response in vitro. The results presented here confirm and extend these observations in several different strains of mice. Administration of nucleoside-modified spleen cells diminishes antibody-forming cells to nucleoside in mice immunized with nucleoside linked to keyhole limpet hemocyanin (KLH). Immune suppression was obtained in all strains except SJL and NZW, which are known to be high responders to denatured DNA. Both the primary and secondary immune responses were suppressed in C57BL/6 mice. Autologous cells exhibit a different ability to function as carriers. Spleen cells are the most effective, and to a certain extent, thymus cells. In contrast, bone marrow cells and red cells fail to induce immune suppression. A strain difference was found between NZB and NZW mice in their susceptibility to immunosuppression by nucleoside-modified spleen cells. Whereas NZB mice are high responders to nucleoside-KLH, they were easily suppressed by nucleoside coupled to spleen cells. In contrast, NZW mice, although relatively low responders to nucleoside-KLH, were not suppressed by administration of nucleoside coupled to spleen cells. Both male and female (NZB × NZW)F₁ mice appeared to behave like the NZW parental strain and were resistant to immunosuppression by nucleoside-modified spleen cells. The significance of this observation for the pathogenesis of murine systemic lupus erythematosus is discussed.     

Functional absence of a B cell subpopulation in ageing New Zealand mice

As has been found for spleen cells from ageing NZB x NZW (B/W) mice, ageing NZB mice were also found to make no antibody when stimulated in vitro with the polyclonal B cell activators (PBA) LPS and PPD. This immune defect was not due to the action of suppressor cells, since old NZB and B/W spleen cells did not suppress the PBA response of young spleen cells. Spleen cells from aged NZB mice were not able to generate antibody-forming cells when stimulated with the thymus-independent antigen, TNP-LPS, but were able to produce antibody in response to another thymus-independent antigen, TNP-AECM-Ficoll, thereby implying that there is a selective functional deletion of a B cell subpopulation in ageing New Zealand mice. The failure of B/W and NZB spleen cells to generate antibody in response to PBA is interpreted as a consequence of a continuing in vivo polyclonal B cell activation accompanying the development of autoimmune disease, leading to a scarcity of B cells available for activation by PBA and by some thymus-independent antigens in vitro.     

CD5 (Ly-1)-negative, conventional splenic B cells make a substantial contribution to the bromelain plaque-forming cell response in CBA and BW mice.

CD5 (Ly-1) B cells are a minor subpopulation in mouse spleen and are thought to be responsible for the production of natural autoantibodies to bromelain-treated autologous erythrocytes (Br-RBC). Here it is shown that substantial numbers of conventional, CD5-negative, splenic B cells also secrete these antibodies in CBA and (NZB x NZW)F1 mice, whereas in NZB and BALB/c mice they are all produced by the CD5 B-cell population. However, stimulation with bacterial lipopolysaccharide in vivo preferentially activates the CD5 B-cell group to anti-Br-RBC antibody secretion.     

The role of suppressor T cells in the expression of autoimmune haemolytic anaemia in NZB mice.

The course of haemolytic anaemia in NZB mice has been altered by injection of spleen cells from diseased mice into younger ones before the onset of clinical disease. Recipients greater than 6 weeks of age developed early-onset autoimmune disease, recipients less than 6 weeks of age developed early-onset autoimmune disease, recipients less than 6 weeks of age recovered from early induced disease and showed a delay in the onset of spontaneous disease as compared with untreated NZB mice. This delay was due to the induction in the young mice of splenic suppressor cells. These cells were non-adherent to nylon wool and suppressed autoantibody formation on transfer to old Coombs-positive recipients. Suppressor cells active against autoantibody formation on transfer to old Coombs-positive recipients. Suppressor cells active against autoantibody-producing cells may be present in young untreated NZB mice, but not in sufficient numbers to suppress autoantibody production on adoptive transfer to Coombs-positive; however, when Ig-negative cells from the spleens of very young NZB mice were transferred together with Ig-positive cells from Coombs-positive donor mice to irradiated NZB recipients, the autoantibody production of the transferred B cells was suppressed in some cases. Suppressor cell activity could also be induced by co-culture of spleen cells from old Coombs-positive and young Coombs-negative NZB mice in vitro.     

Age-related difference by IgG subclass in the response of mice to allogeneic spleen cells.

Inbred mice of various strains, 3–4 months of age and 16 months or older, were given primary injections of allogeneic spleen cells to observe the time of appearance and relative levels of alloantibodies of IgG1 and IgG2 class. In 3–4 month old C3H mice injected with BALB/c spleen cells, IgG2 alloantibodies were present on day 6, before the appearance of alloantibodies of IgG1 class. The IgG2 class alloantibodies then continued to increase in level until day 12. IgG1 class antibodies, which appeared after day 6, also increased during this period. When C3H mice at 16 months of age were similarly injected a difference in response was found in that IgG2 class alloantibodies did not increase in level after the appearance of those of the IgG1 class, but IgG1 class alloantibodies increased until day 12, as in the young mice. At intermediate ages smaller effects in the same directions were observed. Young BALB/c mice injected with C3H spleen cells gave responses similar to those of the young C3H mice. At 16 months, however, the response was not different from that of the young BALB/c mice. At older ages (19–25 months) the response of BALB/c mice was similar to that of the 16-month-old C3H mice described above. CBA mice of various ages which were injected with BALB/c spleen cells showed effects similar to that of the BALB/c mice in that a change of response seen in the older CBA mice, similar to that of the other two strains, did not appear at 16 months of age but did appear later (20–24 months).     

Mercury induces polyclonal B cell activation,autoantibody production and renal immune complex deposits in young (NZB × NZW)F1 hybrids

It is well established that in susceptible mouse strains, chronic treatment with subtoxic doses of mercuric chloride (HgCl₂) induces a systemic autoimmune disease, which is characterized by increased serum levels of IgG1 and IgE antibodies, by the production of anti-nucleolar antibodies and by the development of immune complex-mediated glomerulonephritis. Susceptibility to mercury is partly under the control of major histocompatibility complex genes. To study the susceptibility to mercury further, we investigated the in vivo effects of mercury in young autoimmune disease prone (NZB × NZW)F1 (H-2^d/z) mice prior to establishment of spontaneous autoimmune disease. Mercury-susceptible SJL (H-2^s) mice and mercury low-responder BALB/c (H-2^d) mice were used as positive and negative controls, respectively. In (NZB × NZW)F1 mice, treatment with mercury stimulated an intense antibody formation characterized by increased numbers of splenic IgG1 and IgG3 antibody-producing cells as well as by elevated serum IgE levels. Injection with mercury also induced an increased production of IgG1, IgG2b and IgE antibodies in SJL, but not in BALB/c mice. The mercury-induced IgG1 response in (NZB × NZW)F1 and SJL mice was found to be polyclonal and autoantibodies against double-stranded (ds)DNA, IgG, collagen, cardiolipin, phosphatidylethanolamine as well as antibodies against the hapten trinitrophenol were produced. In addition, SJL, but not (NZB × NZW)F1 or BALB/c mice, produced IgG1 anti-nucleolar antibodies after treatment with mercury. Further studies demonstrated that (NZB × NZW)F1 and SJL mice developed high titers of renal mesangial immune complex deposits containing IgG1 antibodies 3 weeks after injection with mercury. Thus, a mouse strain genetically prone to develop spontaneous autoimmune diseases is highly susceptible to mercury-induced immunopathological alterations.     

The in vitro activity of peritoneal exudate cells from New Zealand Black mice (NZB/B1) in the presence of I125-BSA (bovine serum albumin)

Peritoneal exudate cells from old NZB/B1 mice were found to be more active in taking up I¹²⁵-labelled bovine serum albumin than similar cells from age matched BALB/c, C57B1 and CBA mice. The cells from both young and old NZB/B1 mice were markedly less able to degrade the ingested antigen than cells from the other strains. These observations are discussed in relation to the development of autoimmune phenomena in the NZB/B1 strain.     

Differences between CD8+ T cells in lupus-prone (NZB x NZW) F1 mice and healthy (BALB/c x NZW) F1 mice may influence autoimmunity in the lupus model

Immunization with portions of a murine antibody to DNA induced Ig peptide-reactive peripheral CD8+ inhibitory T (Ti) cells in non-autoimmune (BALB/c x NZW) F1 (CWF1) mice. Those Ti suppressed in vitro production of IgG anti-DNA by lymphocytes from MHC-matched, lupus-prone (NZB x NZW) F1 (BWF1) mice, primarily via secretion of transforming growth factor-beta (TGF-beta). However, splenic CD8+ cells from immunized BWF1 mice failed to suppress anti-DNA. Therefore, BWF1 mice were studied for defects in peripheral CD8+ T cells. The potential to suppress autoimmunity mediated by activated CD4+ helper T and B cells in BWF1 mice was assessed. As BWF1 mice aged, peripheral CD8+ T cells expanded little; fewer than 10% displayed surface markers of activation and memory. In contrast, quantities of splenic CD4+ T and B cells increased; high proportions displayed activation/memory markers. In old compared to young BWF1 mice, splenic cell secretion of two cytokines required for generation of CD8+ T effectors, IL-2 and TGF-beta, was decreased. Immunizing BWF1 mice activated peptide-reactive CD8+ T cells, but their number was decreased compared to young BWF1 or old normal mice. While peptide-reactive splenic CD8+ T cells from immunized BWF1 mice did not survive in short-term cultures, similar CD8+ T cell lines from immunized CWF1 mice expanded and on transfer into BWF1 mice delayed autoimmunity and prolonged survival. Therefore, CD8+ T cells in old BWF1 mice are impaired in expansion, acquisition of memory, secretion of cytokine, and suppression of autoimmunity. Understanding these defects might identify targets for therapy in systemic lupus erythematosus.     

T-cell tolerance induction is normal in the (NZB x NZW)F1 murine model of systemic lupus erythematosus

The (New Zealand black (NZB) x New Zealand white (NZW))F1 (NZB/W) mouse strain spontaneously develops an autoimmune disease characterized by anti-dsDNA antibody production and glomerulonephritis. Although evidence suggests that production of pathogenic autoantibodies is T-cell dependent, the immunological defects that lead to activation of these autoreactive T cells are unknown. In particular, it has not been resolved whether autoreactive T cells become activated in these mice because of a generalized defect in T-cell tolerance induction. Previous work has demonstrated that thymic and peripheral tolerance to strongly deleting antigens are intact in NZB/W mice. In this study we investigate whether these mice possess a more subtle T-cell tolerance defect. To this end, we have produced NZB/W mice carrying a transgene encoding beef insulin (BI) which is expressed at levels close to the threshold for T-cell tolerance induction. In BALB/c mice this transgene produces a profound but incomplete state of BI-specific T-cell tolerance, mediated predominantly by clonal anergy. Comparison of BI-specific tolerance in NZB/W, major histocompatibility complex (MHC)-matched (BALB/c x NZW)F1, and BALB/c BI-transgenic mice clearly demonstrates that T-cell tolerance induction is normal in NZB/W mice. The data suggest that the loss of T-cell tolerance that ultimately supports nephritogenic autoantibody production in NZB/W mice does not result from a generalized defect in T-cell tolerance, and by extension likely results from aberrant activation of specific autoreactive T cells.     

Qualitative difference of anti-DNA antibody-producing cell precursors in the pre-immune B cell repertoire between normal and lupus-prone mice.

The precursor frequency for anti-DNA antibody-producing cells in the pre-immune B cell repertoire was investigated in young female BALB/c and NZW mice, and in young and aged female NZB x NZWF1 (B/WF1) mice. Spleen cells from these mice were diluted serially and stimulated polyclonally in vitro with lipopolysaccharide (LPS) and IL-4 to induce both IgM and IgG1 production. The results demonstrated that there existed virtually no difference in precursor frequency for IgM anti-DNA antibody-producing cells between normal and lupus mice, confirming previous observations made by other investigators. In contrast, the number of precursors for IgG1 anti-DNA antibody-producing cells was much higher in young and old B/WF1 mice than in normal mice. These results suggest that the high frequency of precursors for IgG1 anti-DNA antibody-producing cells in the pre-immune B cell repertoire of B/WF1 mice is a crucial factor for the pathogenesis of systemic lupus erythematosus.