A toxic shock syndrome toxin-1 peptide that shows homology to amino acids 180-193 of mycobacterial heat shock protein 65 is presented as conventional antigen.

Peripheral blood mononuclear cells (PBMC) from the majority of adults (12 out of 18 subjects tested) showed an in vitro proliferative response to a 20 amino acid long peptide (peptide 1, a.a 18-37) derived from TSST-1. In contrast, thymocytes and PBMC from cord blood did not proliferate to this peptide. TSST-1 peptide 1 did not induce IL-1 beta mRNA in monocytes indicating that it does not behave as a superantigen. Proliferation of PBMC to peptide 1 could be blocked by anti-HLA-DR, but not by anti-HLA DP or DQ monoclonal antibodies suggesting that HLA-DR molecules are the restriction elements for the recognition of this peptide by T cells. Studies with subjects of known HLA-DR types showed that all types tested are capable of responding to this peptide. Peptide 1 shows homology to a.a 180-193 of mycobacterial hsp 65 and was shown to stimulate the proliferation of T cell lines and T cell clone specific for the purified protein derivative (PPD) of Mycobacterium tuberculosis. This cross reactivity may confer on TSST-1 the potential to trigger self reactivity and may also contribute to the natural immunity against TSST-1.