Absence of coding sequence polymorphism in the serum amyloid P component gene (Sap) in autoimmune New Zealand black mice

Spontaneous autoimmunity in 129 and C57BL/6 mice-implications for autoimmunity described in gene-targeted mice

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disorder in which complex genetic factors play an important role. Several strains of gene-targeted mice have been reported to develop SLE, implicating the null genes in the causation of disease. However, hybrid strains between 129 and C57BL/6 mice, widely used in the generation of gene-targeted mice, develop spontaneous autoimmunity. Furthermore, the genetic background markedly influences the autoimmune phenotype of SLE in gene-targeted mice. This suggests an important role in the expression of autoimmunity of as-yet-uncharacterised background genes originating from these parental mouse strains. Using genome-wide linkage analysis, we identified several susceptibility loci, derived from 129 and C57BL/6 mice, mapped in the lupus-prone hybrid (129 × C57BL/6) model. By creating a C57BL/6 congenic strain carrying a 129-derived Chromosome 1 segment, we found that this 129 interval was sufficient to mediate the loss of tolerance to nuclear antigens, which had previously been attributed to a disrupted gene. These results demonstrate important epistatic modifiers of autoimmunity in 129 and C57BL/6 mouse strains, widely used in gene targeting. These background gene influences may account for some, or even all, of the autoimmune traits described in some gene-targeted models of SLE.

Several strains of gene-targeted mice develop systemic lupus erythematosus (SLE). Analysis of these strains demonstrates that the genetic background profoundly influences the development of autoimmunity

Genetic Dissection of SLE Pathogenesis: Adoptive Transfer of Sle1 Mediates the Loss of Tolerance by Bone Marrow-Derived B Cells

Sle1 is a potent autoimmune susceptibility locus on chromosome 1 originally identified in a genome scan of testcross progeny between the systemic lupus erythematosus-prone NZM2410 strain and C57BL/6. We subsequently produced B6.NZMc1, a congenic strain carrying the NZM2410-derived Sle1 genomic interval on the B6 background and demonstrated that Sle1 mediated the loss of tolerance to chromatin in both the B and T cell compartments. In this communication, we show by adoptive transfer experiments that the autoimmune phenotypes of Sle1 are completely reconstituted in B6 radiation chimeras receiving B6.NZMc1 bone marrow but not by the reciprocal reconstitution, demonstrating that Sle1 is functionally expressed in B cells. In additional experiments, cotransfer of mixtures of bone marrow derived from B6.NZMc1 and nonautoimmune congenic B6 mice carrying allelic T and B cell markers showed that only B cells derived from B6.NZMc1 bone marrow produced anti-chromatin autoantibodies. In contrast, increased expression of CD69 was equivalent in CD4+ T cells derived from either B6.NZMc1 or congenic B6 bone marrow, suggesting that either T cell population could be activated subsequent to loss of tolerance in the B cell compartment. These findings indicate that the expression of Sle1 in B cells is essential for the development of autoimmunity.

Isoforms of murine and human serum amyloid P component

Isoelectric focusing (IEF) and immunofixation of murine serum amyloid P component (SAP), purified and in serum, showed a distinct and strain-dependent isoform pattern with up to seven bands (pI 5.1-5.7). Neuraminidase treatment caused a shift of the isoforms to more basic pI values, but did not affect their number. When the acute-phase response was analysed in three mouse strains, CBA/J and C3H/HeN initially showed seven SAP isoforms in serum and C57BL/6 J three or four. The responses in all three strains peaked at day 2 and were normalized within 14 days. On days 2 and 4, CBA/J and C3H/HeN mice showed one more acidic isoform and an increase in the concentration of the most basic isoform. C57BL/6 J mice exhibited two to three new isoforms during the acute-phase response. This appears to be the first demonstration of the physiological existence of SAP isoforms. In contrast, demonstration of isoforms of human SAP required the presence of urea and higher SAP concentrations. TEF and immunofixation of SAP monomers showed five to eight isoforms, ranging from pI 4.7-5.7. IEF of SAP in human serum resulted in a less distinct pattern and more acidic isoforms. As with murine SAP, neuraminidase treatment caused a shift of the isoforms, but no reduction in isoform number. Two-dimensional gel electrophoresis confirmed the existence of multiple isoforms of human SAP monomers.