NZB Mice Research Articles

Preferential reactivity of autoantibodies in murine lupus NZB mice to neuraminidase-treated monosialogangliosides on B cells of mouse spleen

When analyzed by flow cytometry, reactivity of IgM autoantibodies in sera from NZB mice to spleen B cells, but not to T cells, from BALB/c mice was remarkably increased after treatment of the cells with Vibrio cholerae neuraminidase. By TLC immunostaining with the antibodies, neither neutral nor acidic glycosphingolipids from both BALB/c and NZB mouse spleens were found to be reactive, but after neuraminidase treatment of the TLC plate, prior to the immunostaining, three components became reactive. All of the reactive glycosphingolipids were found to carry a single sialic acid residue and were at a concentration less than 1.3% of the total lipidbound sialic acids. Their mobilities on TLC plate were close to those of IV 3 NeuAcnLc 4Cer, IV 3 NeuAcII 3 NeuAcGg 4Cer, and IV 3 NeuAcII 3 NeuAc 2Gg 4Cer. In addition, the monosialogangliosides, which became reactive with the autoantibodies after neuraminidase treatment, were found to be predominantly distributed on B cells from BALB/c mice spleen, but not on T cells by TLC immunostaining. These studies demonstrate that the majority of IgM autoantibodies to spleen lymphocytes in sera from NZB mice might react preferentially to terminal sugar residues of three new glycosphingolipids masked by a single sialic acid on B cells, but not on T cells.

Transplantation of wheat germ agglutinin-positive hematopoietic cells to prevent or induce systemic autoimmune disease.

Hematopoietic stem cell defects are thought to be involved in the etiopathogenesis of systemic autoimmune disease. Positively selected, stem cell-enriched populations of wheat germ agglutinin-positive (WGA+) low-density bone marrow and fetal liver cells from normal and autoimmune-prone mice were used to determine whether reciprocal transplantation of stem cells between normal and autoimmune-prone mice inhibits or causes development of autoimmune disease. NZB recipients of DBA/2 stem cell populations analyzed greater than 100 days after bone marrow or fetal liver cell transplantation showed decreased levels of anti-DNA antibodies and decreased glomerular lesions when compared with nontreated NZB mice or NZB recipients of NZB stem cell preparations. Female DBA/2 recipients of WGA+ NZB bone marrow cell or fetal liver cell transplants exhibited elevated serum autoantibody levels and developed glomerular lesions characteristic of NZB mice when analyzed greater than 100 days after transplantation. These pathological disturbances were not observed in DBA/2 recipients of DBA/2 stem cell preparations. The data indicate that WGA+ stem cells from autoimmune-prone NZB mice contain the genetic defects responsible for the development of systemic autoimmune disease.

Monoclonal antibodies against human anti-F(ab′) 2 antibodies react with light chain epitopes

Anti-F(ab′) 2 antibodies affinity isolated from sera of patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), or normal SLE relatives were used to produce monoclonal antibodies (mAbs) in Balb c and NZB mice. Four of five mAbs showed only primary light chain specificity. Only one mAb produced in an NZB mouse against anti-F(ab′) 2 from a single SLE patient showed anti-μ-chain specificity. Parallel identical control immunizations with IgG or a single human IgG κ myeloma produced mAbs with a predominant γ-chain Fc fragment specificity. Anti-light chain specificity of mAbs was demonstrated to involve epitopes requiring tertiary structure of the entire light chain instead of antigens confined to C κ λ or V κ λ fragments. Anti-κ specificity of three mAbs was extremely similar but not identical to that defined by anti-Kml allotyping systems. No evidence was obtained with any of the mAbs produced for antigens unique to SLE or RA anti-F(ab′) 2 antibodies. The light chain antigenic prominence of many anti-F(ab′) 2 antibodies may reflect structural features shared by this group of immunoglobulins some-how important for their biologic function.

Correlation between the occurrence of lupus nephritis, anti‐erythrocyte autoantibodies and Vx haplotype in NZB × 129/J and NZB × SM/J recombinant inbred murine strains

The NZB mouse is genetically predisposed to the development of autoimmune disease that resembles the human autoimmune systemic lupus erythematosus and autoimmune hemolytic anemia, with increased titers of anti-DNA, and Coombs' autoantibodies. The various autoimmune traits are controlled separately by a limited number of genes. Genetic studies have shown that several immune loci are involved in autoimmunity: T cell abnormalities, H-2 complex and immunoglobulin genes have been implicated. In this report, we present evidence for a significant correlation of NZB V kappa 1 haplotype defined by restriction fragment length polymorphism analysis with anti-erythrocyte autoantibodies in NZB x 129/J and NZB x SM/J recombinant inbred lines.

Ionic Binding Characteristics of Monoclonal Autoantibodies to DNA from NZB.H-2 bm12 Mice

NZB (H-2d) mice are well known for the production of IgM autoantibodies to ssDNA. However, an F1 cross between NZB and either NZW or SWR mice is required to produce IgG nephritogenic antibodies to dsDNA and glomerulonephritis. The contribution of parental class II loci in the hybrid mice is clearly important to the development of anti-dsDNA antibodies. In contrast, NZB mice congenic with the Iabm12 mutation develop IgG autoantibodies to dsDNA despite being homozygous for Ia. As a part of our effort to examine the mechanisms of disease development in NZB.H-2bm12 mice, we have generated a panel of monoclonal antibodies against nucleic acids. A subgroup of these antibodies exhibited strong electrostatic interaction with nucleic acids as evidenced by inhibition of their binding by a moderate increase in ionic strength. Interestingly, the effect of salt was either all or none; e.g., antibodies were either markedly inhibited or virtually unaffected. The importance of this ionic interaction was highlighted by analysis of DNA binding of antibodies from serum and nephritic kidneys of NZB.H-2bm12 mice. Antibodies specific for ssDNA, which are common in NZB mice and not associated with nephritic lupus, are largely unaffected by salt. However, serum and kidney eluted IgG antibodies specific for dsDNA were markedly inhibited by salt. We postulate that B cell clones whose antibodies exhibit electrostatic interaction with DNA are preferentially expanded during the course of lupus in NZB.H-2bm12 mice and that such antibodies contribute significantly to glomerulonephritis.

The contribution of I-Abm12 to the production of autoantibodies to dsDNA.

The development of IgG autoantibodies to dsDNA in NZBxNZW F1 (NZB/W) and NZBxSWR F1 (SNF1) mice have been linked to specific alleles of MHC class II genes contributed by the NZW and SWR parents respectively. Recently, our laboratory has shown that the introduction of the bm12 mutation into NZB mice (NZB.H-2bm12) results in mice which are phenotypically similar to NZB/W F1 mice and, in particular, develop IgG anti-dsDNA antibodies. A variety of immune abnormalities have been described in autoimmune NZB (H-2d) mice. It is, however, unclear at present, whether all these abnormalities are due to the influence or effect of a single set of linked genes or due to multiple genes. It was reasoned that NZB.H-2bm12 mice provide a unique opportunity to examine this issue. Specifically, we bred a series of five different F1 colonies of mice: (a) NZB.H-2bm12/b F1; (b) NZB.H-2bm12/d F1; (c) NZB-H-2b/d F1; (d) NZB-H-2bm12 x B6.C-2bm12 F1 (NZB/B6.H-2bm12 F1); and (e) NZB x B6.C-H-2bm12 F1 (NZB/B6.H-2d/bm12 F1) mice. All groups of mice were serially followed for the appearance of IgM and IgG anti-ssDNA and anti-dsDNA antibodies, splenic CFU-B, spontaneous secretion of IgM, FMF analysis, proteinuria and survival. We report herein that H-2bm12 genes have a dominant influence on the appearance of IgG anti-dsDNA antibodies. In contrast, antibodies to ssDNA, IgM secreting cells, CFU-B and Ly-1 B cells are linked to genes from the NZB background. Finally, we particularly note an absence of IgG antibodies to dsDNA in NZB-H-2b/d F1 mice.

Influence of Host Environment on Growth of Clonal CD5 + B (Lyl + B) Cells

Autoimmune NZB mice have increased percentages of CD5+B (Lyl+B) cells in both the spleen and peritoneum. We have previously reported that as NZB mice age they develop a clonal population of hyperdiploid CD5+B cells in the spleen. These cells can readily be transplanted into unirradiated recipients. The growth characteristics of such transplanted hyperdiploid NZB spleen cells were examined in different recipient strains to determine if the immunological status of the host environments affected the growth of the clonal CD5+B cells. Young NZB and NZB.xid recipients (lacking hyperdiploid CD5+B cells) allowed growth and expansion of unpassaged CD5+B cells derived from primary NZB mice. Similarly, (NZBxDBA/2) and (NZBxBALB/c) F1 recipients allowed for expansion of CD5+B cell clones from primary sources. In a separate experiment, T cell-depleted NZB spleen cells containing a hyperdiploid CD5+B cell clone were transferred to SCID mice. The SCID environment supported the growth of the primary clone. None of these recipients normally have elevated CD5+B cells, yet these recipients allowed growth of primary transferred hyperdiploid cells. However, a difference in the ability of these recipient strains in their ability to expand multiply passaged CD5+B cell clones was observed. These results indicate that while hyperdiploid CD5+B cells are difficult to be maintained in culture, they can readily be passaged in vivo. The host environment may provide growth factors or signals for endogenous growth factors. Although the CD5+B clones arise initially in a hyperactive autoimmune environment, a hyperimmune environment is not necessary to support their growth. Transferred CD5+B cells affect the recipient environment and reduce the percentages of normal B cells.

NZB serum factor (NZB-SF): B precursor cell maturation factor identified in murine lupus: I. Identification of 60-kDa glycoprotein as the major component from both spleen cell supernatant and serum

NZB serum factor (NZB-SF), initially identified in sera of very young NZB mice, can enhance maturation and proliferation of sIg pre-B cells in marrow. In the present study, spleen cell supernatant from young NZB mice was used as a source of NZB-SF. NZB mice were treated with Corynebacterium parvum 2 weeks prior to sacrifice, and harvested spleen cells obtained at sacrifice were cultured for 24 hr in serum-free medium. One liter of spleen cell supernatant prepared in this way contained NZB-SF-like activity equivalent to that present in 10 ml of serum collected from young NZB mice. NZB-SF was purified on an affinity Chromatographie column conjugated with mouse IgG 1 monoclonal antibody (mAb) against NZB-SF. The purified NZB-SF had pI 7.8 and showed one major band of 60 kDa and a faintly stained 35-kDa band upon SDS-PAGE under nonreducing conditions. The 60-kDa NZB-SF extracted from the gel slice was also more potent in dot blot ELISA (>100 times) than the 35 kDa NZB-SF and was biologically active. After endoglycosidase F treatment, but not after treatment with a reducing agent (2-ME), the two bands merged into a single band at the 15-kDa position. Amino acid sequence analysis of endo-F treated NZB-SF indicated that the N-terminus of this protein is blocked. Serological and functional studies of affinity-purified NZB-SF have revealed that NZB-SF is distinguishable from IL-1α, IL-2, IL-3, IL-4, IL-5. IL-6, CSF-GM, IFN-γ, and TNFα. Therefore, a major component of NZB-SF(s) in the spleen cell supernatant may be an apparently novel 60-kDa glycoprotein with a single amino acid backbone. Sera and spleen cell supernatants from normal strains of mice (DBA/2, B6. or BALB/c) were also applied to the immuno-affinity column used to purify NZB-SF. It was found that trace amounts of NZB-SF are present also in serum of normal strains of mice and that spleen cells of these mice can also produce NZB-SF in vitro following stimulation with C. parvum- In SDS-PAGE, the 60-kDa NZB-SF is also the major component of NZB-SF in normal strains of mice. These results suggest that the 60-kDa NZB-SF may be of physiological importance in B cell differentiation and that this physiological factor is overproduced in autoimmune-prone NZB mice.

Preferential Proliferation of Anti-Dna Producing Cells of Nzb Mice in Nzbxzd Recipients

B cells from autoimmune NZB mice were transferred into unmanipulated non-autoimmune NZB.xid mice. The number of antibody-producing cells against various antigens in recipient mice was monitored at varying time after cell transfer using ELISPOT assay. NZB B cells producing antibody against all antigens we examined were able to proliferate in NZB.xid mice, which supports the idea of polyclonal B cell activation. However, anti-DNA producing cells proliferated most rapidly, and anti-BrMRBC producing cells proliferated more rapidly than B cells of other antigenic specificities. The percentage of anti-DNA producing cells in total immunoglobulin-producing cells increased over time whereas the percentage of anti-ovalbumin producing cells kept the same level. This indicates directly the preferential proliferation of NZB anti-DNA producing cells in NZB.xid mice. The result shows the responsibility of antigen-specific stimulation or activation on autoimmunity in the context of polyclonal B cell activation.

Hemolytic anemia related to an IgM autoantibody to phosphatidylcholine that binds In vitro to stored and to bromelain-treated human erythrocytes

Both normal and autoimmune mice have IgM natural autoantibodies to bromelain-treated erythrocytes in which phosphatidylcholine (PTC) becomes exposed. At one stage this antibody may participate in the genesis of autoimmune hemolytic anemia in the NZB mouse. We have recently studied a patient with hemolytic anemia who had persistently high serum titers of IgM anticardiolipin antibodies (aCL) that were also demonstrated in a hemolysate of his erythrocytes obtained at the time of the anemia. We affinity-purified the antibody and sought its binding to normal human bromelain-treated erythrocytes (BrE) because of the IgM isotype of the antibody, since cardiolipin is not a constituent of the erythrocyte wall, and because the anionic phospholipids, with which aCL are known to cross-react, are not located at the outer leaflet of the erythrocyte membrane. We found binding of the antibody to HBrE in their hemolysates and by flow cytometry. We also demonstrated that the aCL cross-reacted extensively with PTC, as well as with other anionic or zwitterionic phospholipids. The purified IgM antibody lysed BrE in the presence of complement and also bound to in vitro-aged erythrocytes. Because this patient had no other evidence of systemic lupus erythematosus or any other autoimmune condition, his disease may represent a variant of the recently described primary antiphospholipid syndrome.

Effects of recombinant human erythropoietin on haemolytic anaemia in mice

The effects of repeated administration of recombinant human erythropoietin (rHuEPO) were investigated in mice with haemolytic anaemia. Mice with haemolytic anaemia induced by phenylhydrazine (PHZ mice) were examined as an acute model and New Zealand black mice (NZB mice) at 13 months of age were examined as a chronic model. The plasma erythropoietin (EPO) level in PHZ mice was high and showed a strong inverse correlation with the Hb in the anaemia development period. However, it was relatively low in the recovery period from anaemia. On the other hand, the plasma EPO level in NZB mice showed a simple inverse correlation with the Hb. The rHuEPO was injected every day for a week into these mice. While a high plasma EPO level was maintained in PHZ mice, no significant effect was observed by injection with rHuEPO at dose of 600 IU/kg. However, in the recovery period from anaemia, RBC and haemoglobin in PHZ mice were increased by the rHuEPO treatment and recovered more quickly to their normal levels. In NZB mice, RBC and haemoglobin were also increased by treatment with rHuEPO at dose of 600 IU/kg. Anti-RBC autoantibodies and anti-EPO antibodies did not increase, while RBC and plasma EPO levels were increased by the rHuEPO treatment. These results suggest that some types of haemolytic anaemia are not always combined with high endogenous EPO levels and that exogenous rHuEPO may be effective for use in the treatment of haemolytic anaemia.

Defect of Binding of Nuclear Factors from Embryonic and Newborn Brain Nuclear Extracts from Autoimmune NZB Mice with the Rat Neuropeptide Y Gene Promoter

Defect of Binding of Nuclear Factors from Embryonic and Newborn Brain Nuclear Extracts from Autoimmune NZB Mice with the Rat Neuropeptide Y Gene Promoter

Chronic in vivo depletion of CD4 T cells increases both serum IgM levels and the expressed frequency of anti-ssDNA precursors in both NZB and [formula omitted] mice

Chronic depletion of CD4 T cells has been employed as therapy in a number of models of autoimmune disease, including spontaneously autoimmune NZB W mice. In the present study, we evaluated the influence of CD4 depletion on the production of IgM and IgM anti-ssDNA. Beginning at 8 weeks of age, NZB and DBA 2 mice received 12 weekly injections of monoclonal antibody GK1.5 (anti-CD4) or normal rat IgG. In both strains, CD4 T cell depletion resulted in an increase in serum IgM. Anti-ssDNA precursors, which are increased in NZB mice, were further increased by depletion of CD4 T cells. The DBA 2 mouse expresses anti-ssDNA precursors relatively infrequently; however, CD4 T cell depletion resulted in a significant increase in the expression of these autoantibody precursors as well as an increase in the RNA content of splenic B cells. These results indicate that although CD4 T cell depletion ameliorates clinical manifestations of autoimmunity in some situations, this treatment may also increase serum IgM levels and the production of anti-ssDNA autoantibodies.

Identification of a new V kappa gene family that is highly expressed in hybridomas from an autoimmune mouse strain.

We have identified a new murine V kappa family that contains five to seven members, one member of which encodes the L chain V region of an anti-dsDNA antibody produced by a BALB/c hybridoma, C8.5. The cloned C8.5 V kappa gene exhibits highest homology with a human V kappa gene that was cloned from a nonproductive rearrangement but has never been seen in an expressed repertoire. Because this family was first identified in an autoantibody, we studied its expression in an autoimmune mouse strain. This V kappa family is expressed in 20% of hybridomas from NZB mice.

Possible immunoregulatory role for CD5+B cells

CD5 + B cells represent a subpopulation of B cells which have the characteristic of employing unmutated immunoglobulin variable region genes. These cells are found to be increased early in ontogeny. The percentage of CD5 + B cells is highest in the fetus and decreases after birth. The antibodies produced by CD5 + B cells are polyreactive and are the natural autoantibodies. These autoantibodies may not be pathogenic. CD5 + B cells are elevated in certain autoimmune disease states and are the malignant cell type in B-CLL, with a strong genetic component involved in determining elevated CD5 + B cell states. Elevated CD5 + B cells are found in immunodeficient states (young, aged, and autoimmune). CD5 + B cells may normally act as a first-line defense against invading foreign pathogens but are not involved in the specific immune response. There is some evidence, at least in newborns, that CD5 + B cells may affect the emerging B cell repertoire of conventional B cells via idiotype cascade. However, the action of CD5 + B cells in the newborn may be quite different than their activity in the adult. Nonimmunoglobulin-producing CD5 + B cells may be immunosuppressors. In this report, a unique subpopulation of CD5 + B cells was investigated. These cells were found only in the spleens of aged NZB mice. The CD5 + B cells were clonal and possessed extra chromosomes and did not appear to be producing antibodies. These cells were capable of rapid proliferation in unirradiated recipients. By taking advantage of this proliferative capability, the effect of exogenous clonal CD5 + B cells on recipient immune system was evaluated. Clonal CD5 + B cells from NZB mice were immunosuppressive and decreased the numbers of conventional B cells as well as the level of "natural antibodies." In summary, CD5 + B cells may play different roles in the immune system depending upon environment, age, and their differentiation state (i.e., proliferation versus antibody secretion). The natural antibody produced by CD5 + B cells may be involved in maintenance functions such as removal of dead cells and first-line defense mechanisms. In addition, CD5 + B cells may themselves regulate the immune system and produce a factor which is immunosuppressive. An understanding of the various functions of CD5 + B cells may elucidate fundamental immunoregulatory circuits.

Production of a monoclonal allo‐antibody to murine natural cytotoxic cells

A mouse IgG1 monoclonal antibody (1C4), which recognizes a cell surface molecule on murine natural cytotoxic (NC) cells was produced. By flow cytometry, 1C4 preferentially reacted with less than 5% of fresh CBA spleen cells and 20-50% of CBA-interleukin-3 (IL-3) cells, an in vitro derived NC-like cell line. In vitro treatment of spleen cells from a number of inbred mouse strains either with 1C4 alone or 1C4 coupled to dynabeads markedly decreased or abolished NC activity of the cells against 51Cr-labelled WEH1-164 targets. Splenic NC activity of these same mouse strains was also reduced or abolished by in vivo administration of 1C4. The effect was evident within 2 h of treatment and persisted for at least 1 week. In contrast 1C4 had little or no effect on splenic NK activity against 51Cr-labelled YAC-1 targets over the same range of experiments in vitro and in vivo. Results of strain surveys for both in vitro and in vivo reduction of splenic NC activity by 1C4 treatment showed that CBA, C57BL/6, BALB/c and NZB mice were positive and CE and DBA/2 mice were negative, indicating that 1C4 recognizes an allo-antigen on mouse NC cells. This allo-antibody has been designated NC-1.1, and thus 1C4 is an anti-NC-1.1 monoclonal antibody.

The BM12 mutation and autoantibodies to dsDNA in NZB.H-2bm12 mice.

Molecular and genetic tools have been used to shed light on the genes that contribute to susceptibility to murine lupus and the mechanisms that lead to immunopathology. The MHC genes and their products have been consistently shown to contribute toward the development of disease. To understand the contribution of MHC-class II genes, our laboratory had derived two inbred strains of mice, NZB.H-2bm12 and NZB.H-2b. These new colonies of mice were studied and compared in the 10th generation backcross; inbreeding was serially followed by H-2 typing, responses to beef/porcine insulin, and the presence of the B6 Ig allotype, IgG2ab. Of great interest is the finding that NZB.H-2bm12, in contrast to NZB.H-2b or NZB (H-2d), mice develop high titer autoantibodies to dsDNA. This result is unique because NZB (H-2d) mice, unliked NZB x NZW (NZB/W F1) or NZB x SWR (SNF1) hybrids do not develop autoantibodies to dsDNA, even after immunization. NZB mice, in contrast, are characterized only by autoantibodies to ssDNA. Our observation is also striking because the gene conversion that resulted in the I-A beta bm12 mutation occurred at amino acid residues 68, 71, and 72 of I-E beta b. Recently the contribution of NZW to accelerated autoimmunity in the NZB x NZW F1 hybrid has also been linked to H-2 and a single amino acid change at amino acid 72 of I-E beta. Thus, amino acid residue 72 may be a hot spot for disorders of immune regulation when superimposed on the appropriate genetic background. NZB mice expressing the I-Abm12 mutation will allow specific dissection of the requirements for autoantibody production to dsDNA uncomplicated by heterozygosity.

Stochastic pairing of heavy-chain and kappa light-chain variable gene families occurs in polyclonally activated B cells.

Frequencies of 25 immunoglobulin heavy-chain and kappa light-chain variable (VH + V kappa) gene-family pairings expressed in splenic B-cell populations were determined by hybridization of VH- and V kappa-family-specific DNA probes to mitogen-induced B-cell colonies from C57BL/6 mice or hybridomas derived from BALB/c and NZB mice. Both analyses support the conclusion that VH and V kappa gene families pair without bias; as would be expected for random association, the frequencies of specific VH + V kappa pairs may be estimated by the product of the independent VH and V kappa frequencies. Based upon the frequencies at which 9 VH and 12 V kappa gene families are expressed, we calculated the expected usage for approximately 100 VH + V kappa family pairings in neonatal and adult C57BL/6 mice. Variability in the expression of such VH + V kappa pairings is considerable; pairs representing greater than 10% to less than 0.01% of the splenic B-cell population occur. This variability is most pronounced in the neonate, where 6 VH + V kappa family pairs account for nearly 40% of all mitogen-reactive B cells. As the neonate matures, the distribution of frequencies for VH + V kappa pairings becomes more nearly uniform. This process may underlie the patterned acquisition of humoral immune responsiveness.

Evidence for major alterations in the thymocyte subpopulations in murine models of autoimmune diseases

Thymocytes can be divided into four major subpopulations: CD4 +CD8 + (double-positive), CD4 −CD8 − (double-negative), CD4 +CD8 − (CD4 +) and CD4 −CD8 + (CD8 +) cells. Recent studies have shown that T-cell development in the thymus progresses as: CD4 −CD8 − → CD4 +CD8 + → CD4 + or CD8 + cells. In the present study we investigated these and other subpopulations of thymocytes in autoimmune MRL-+/+, MRL- lpr lpr , C57BL 6 - lpr lpr , BXSB and NZB mice before (1-month old) and after (4–6-months old) the onset of lymphadenopathy and autoimmune disease. All the autoimmune strains at one month of age and other H-2, sex and age-matched controls (C3H, DBA 2 , and C57BL 6 ) demonstrated normal proportions of thymocyte subsets with ∼75% double-positive cells, 5–7% double-negative cells, 11–15% CD4 + cells and 3–5% CD8 + cells. By 4–6 months of age, MRL-+/+ mice demonstrated a moderate increase in double-negative cells (∼13%) and a decrease in double-positive cells (∼46%). Interestingly, in the presence of the lpr gene, as seen in MRL- lpr lpr mice, the double-negative cells increased to ∼47% and the double-positive cells decreased to ∼16%. In contrast, 4–6-month-old C57BL 6 - lpr lpr mice failed to demonstrate any alterations in the thymocyte subsets thereby suggesting that background genes, in addition to the lpr gene, played a role in the thymocyte differentiation. BXSB male mice with severe lymphadenopathy behaved very similarly to MRL- lpr lpr mice, inasmuch as their thymus contained ∼48% double-negative cells and only ∼8% double-positive cells. In contrast to MRL- lpr lpr and BXSB strains, NZB mice at 6 or 10 months of age had normal composition of thymocyte subsets. In MRL and BXSB animals, although there was a significant increase in CD4 + cells (∼23–33%), due to a consequent increase in CD8 + cells (∼11%), the ratio of CD4 +:CD8 + cells remained 2–3:1, similar to that seen in normal mice. Furthermore, using the J11d marker expressed by the majority of the double-negative and all double-positive thymocytes but not by mature functional T cells, we confirmed the above findings and demonstrated further that MRL- lpr lpr mice at 4–6 months of age had an increased percentage of J11d − double-negative cells and a decrease in J11d + double-negative cells. The present study demonstrates for the first time the existence of a common defect in T-cell differentiation in the thymus of autoimmune strains of mice which is dependent on the genetic background and other accelerating factors responsible for inducing autoimmune disease.

Opponent strain effect on eliciting attacks in NZB mice: Physiological correlates

In agonistic encounters between male mice, the characteristics of the opponent may influence the attacking behavior of its partner. The present study shows that the opponent's ability to elicit attacking behavior in NZB males is strain dependent. BALB/c opponents elicit attacks more frequently, earlier and more intensively than C57BL/6 males. Plasma testosterone concentration was found to be higher in BALB/c than in C57BL/6 intact males. The weight of seminal vesicles in castrated males of both strains increased with injections of either 10- or 250-μg testosterone propionate (TP). This response was greater in BALB/c with the higher TP dose. The submandibular glands reacted to TP only in castrated BALB/c males with the higher dose. Furthermore, BALB/c males produced more marking secretions than C57BL/6 males. These results suggest that for these two strains, a higher testosterone sensitivity and a greater production of secretions are associated with a higher probability of opponents to elicit attacks. Genetic hypotheses on the underlying mechanisms are discussed.