A defect in Marco expression contributes to systemic lupus erythematosus development via failure to clear apoptotic cells.

Systemic lupus erythematosus is a multisystem autoimmune disease characterized by the production of numerous antinuclear autoantibodies and inflammatory mediators. The BXSB mouse strain is an excellent model of the disease. Previous work has determined a number of important disease susceptibility intervals that have been isolated in separate congenic strains. Here, we have combined expression data from those strains with functional analyses to demonstrate that reduced expression of the innate scavenger receptor Marco (macrophage receptor with collagenous structure) is a primary event in BXSB mice, that reduced mRNA expression is mirrored at the protein level, and that this results in a significant alteration in function. We have confirmed a role for Marco in the clearance of apoptotic cells and a generalized defect in both endocytosis and phagocytosis. The failure to clear apoptotic cells has previously been linked to the development of systemic lupus erythematosus. However, the use of congenic mice with limited phenotypes in this study has enabled us to propose that in the case of Marco at least, disease results from the production of anti-dsDNA Abs.

CD40 can costimulate human memory T cells and favors IL-10 secretion.

Optimal proliferation of T cells, although initiated via ligation of the CD3/TCR complex, requires additional costimulatory signals. While the most well-defined in vitro pathway of costimulation is via the B7 family of molecules, a large body of data clearly demonstrates an in vivo role for the CD40/CD154 pathway in transplantation, autoimmunity and allergy. We have examined the role of CD40 as an independent costimulatory molecule by generating a panel of transfected human fibroblasts expressing DR1 with either CD80, CD86 or CD40. Functional assays using allogeneic CD4(+) T cells as responders demonstrated that CD40 was capable of costimulating CD4(+) T cell proliferation particularly in the CD45RO subset. Costimulation by CD40 induced much higher levels of IL-10 than were induced by B7-expressing cells. On day 3 the dominant costimulation was provided by CD40, while by day 5 this was overshadowed by CD80 and CD86. Nonetheless, the provision of costimulation by CD40 was enough to expand an alloreactive T cell line. These results were confirmed in experiments using primary cultures of CD40(+)CD80/CD86(-) renal tubular epithelial cells as the stimulator population. Thus, CD40 is capable of functioning independently (in the absence of B7) as a costimulatory molecule both in terms of proliferation and cytokine release. The data have interesting implications concerning the consequences of antigen presentation by tissue parenchymal cells.