The interaction between staphylococcal superantigen-like proteins and human dendritic cells

Staphylococcus aureus produce a family of exotoxins (staphylococcal superantigen like proteins, SSLs) with structural, but not functional, homology to superantigens. These proteins have previously been shown to interact selectively with antigen presenting cells, including dendritic cells. The functional consequences of this interaction are now explored. SSL7 and 9 had no effect on viability or morphology of dendritic cells. The proteins did not induce dendritic cell maturation, as measured by cell surface phenotype. Exposure to SSL did not alter the ability of dendritic cells to take up FITC-dextran. Finally, exposure to SSLs did not impair the ability of the dendritic cells to stimulate allogeneic or antigen specific T cell responses. However, dendritic cells loaded with SSL7 or 9 were able to stimulate a T cell proliferative response in 3/8 healthy individuals tested. Sera from nine out of 10 individuals tested contained antibodies against both SSL7 and SSL9, and the response to each SSL was specific and not cross-reactive. The results demonstrate that SSLs are immunogenic in humans at both the B and T cell level, but it remains unclear whether this response is to the benefit of the bacterium or the host.