Human peripheral blood lymphocyte activation by protein A from Staphylococcus aureus

Abstract

Mitogenesis and polyclonal ig production in peripheral blood lymphocyte cultures activated with Formalin-fixed or autoclaved protein A-containing S. aureus were studied. Direct evidence for a dissociation between cell proliferation and polyclonal ig production was found; S. aureus was not mitogenic after being autoclaved but retained the ability to stimulate B cells to produce ig. Trypsin-treated S. aureus lost its binding site for ig G, but its mitogenicity was not altered; thus, the protein A binding site for ig G on the bacterial cell wall is not required for the stimulation of lymphocyte proliferation. A dissociation between cell proliferation and polyclonal ig production induced by protein A coupled to Sepharose CL- 4B was also shown. The presence of 3 distinct active sites on the protein A molecule was suggested: 1 that binds ig G molecules, 1 that stimulates cell proliferation and 1 that stimulates polyclonal ig production.