Autoantibodies inhibit interleukin-7-mediated proliferation and are associated with the age-dependent loss of pre-B cells in autoimmune New Zealand Black mice

Surface IgM⁺B220⁺ B cell precursors can be categorized as either leukosialin (CD43/S7) negative (late stage pre-B cells) or positive (pro- B/early pre-B cells). In autoimmune New Zealand Black (NZB) mice, bone marrow small pre-B cells (IgM^-CD43^-B220⁺) and pro-B/early pre-B cells (IgM^- CD43⁺B220⁺) declined significantly with age. In particular, subpopulations of pro-B/early pre-B cells expressing the heat stable antigen (HSA) were found in lower proportions with age. Significant decreases in interleukin-7 (IL-7) colony forming units (CFU) were also seen in NZB mice by 6 to 8 months of age and accompanied alterations in the numbers of pro-B and pre-B cells in bone marrow. Concomitant with reduced numbers of B lineage precursor cells and IL-7 CFU in viva, NZB mice produced serum IgM antibodies that strongly inhibited IL-7 CFU responses in vitro. Two monoclonal IgM antibodies (5G9, 2F5) derived from LPS stimulated 10-month-old NZB splenocytes recognized pre- B cell surface antigens on both pre-B cell lines and on IL-7 stimulated bone marrow pro-B/pre-B cells. However, these monoclonal antibodies (MoAb) failed to significantly stain ex viva bone marrow cells. The 5G9 and 2F5 MoAbs also partially inhibited IL-7 CFU in vitro. These results suggest that NZB bone marrow becomes increasingly deficient in B cell precursors and especially in IL-7 responsive pre-B cells with age. IgM serum antibodies and monoclonal IgM antibodies derived from older NZB mice inhibit pre-B cell growth to IL-7. The production of such autoantibodies may interfere with B cell development in aging NZB mice by preventing IL-7-mediated proliferation.