Mechanisms of immune complex-mediated experimental glomerulonephritis: possible role of the balance between endogenous TNF and soluble TNF receptor type 2.

In an experimental model of immune-complex-mediated glomerulonephritis, mice excreted increased levels of urinary protein starting three days after the induction. Mice lacking the TNF receptor type 2 (TNFR2) were protected from early proteinuria and enhanced mortality. Analysis of the molecular basis of the mechanisms of glomerulonephritis revealed that naïve mice continuously excrete soluble TNF-neutralizing TNFR2 in urine. Mice kept in a specific pathogen-free environment did not go on to develop early proteinuria or enhanced mortality, following induction of glomerulonephritis. TNFR2-deficient mice were protected from early proteinuria and enhanced mortality only when housed conventionally. Mice producing human TNFR2 that can be activated by mouse TNF, in addition to mouse TNFR2, did not demonstrate enhanced susceptibility to the lethal effects of glomerulonephritis, indicating that pro-inflammatory signalling via TNFR2 does not account for a sensitizing effect. Finally, we suggest that the protective effect seen in mice lacking TNFR2 results rather from environment-induced attenuation by low dose bacterial endotoxins than from missing pro-inflammatory signalling via the TNFR2.

Sepsis leads to a reduced antigen-specific primary antibody response.

Immunosuppression, impaired cytokine production and high susceptibility to secondary infections are characteristic for septic patients, and for mice after induction of polymicrobial septic peritonitis by sublethal cecal ligation and puncture (CLP). Here, we demonstrate that CLP markedly altered subsequent B-cell responses. Total IgG and IgM levels, as well as the memory B-cell response, were increased in septic mice, but antigen-specific primary antibody production was strongly impaired. We found that two days after CLP, CD11b(+) splenocytes were activated as demonstrated by the increased expression of activation markers, expression of arginase and production of NO by immature myeloid cells. The in vivo clearance of a bacterial infection was not impaired. DCs demonstrated reduced IL-12 production and altered antigen presentation, resulting in decreased proliferation but enhanced IFN-γ production by CD4(+) cells. CD4(+) T cells from mice immunized on day 2 after CLP showed reduced Th1 and Th2 cytokine production. In addition, there was an increase in Treg cells. Interestingly, levels of immature B cells decreased but levels of mature B cells increased two days after CLP. However, adoptive transfer of naïve CD4(+) T cells, naïve B cells, or naïve DCs did not rescue the antigen-specific antibody response.