MULTIPLE LIGAND INTERACTIONS FOR BACTERIAL IMMUNOGLOBULIN-BINDING PROTEINS ON HUMAN AND MURINE CELLS OF THE HEMATOPOIETIC LINEAGE

A group of bacterial Ig-binding surface proteins were studied: protein H and M1 are from Streptococcus pyogenes and interact with IgG, protein L is expressed by Peptostreptococcus magnus and shows affinity for Ig light chains, whereas protein LG is a chimeric construction combining the binding properties of protein L with the IgG-binding activity of protein G from group C and G streptococci. Proteins L and H coupled to Sepharose were mitogenic for human peripheral blood lymphocytes (PBL) and mouse splenic B cells, but not when added in soluble form. Differentiation to Ig secretion was induced by protein H-Sepharose in mouse splenic B cells but not in human PBLs. In FAGS analysis FITC-labelled protein H stained virtually all CD19(+) cells in human peripheral blood as well as a majority of the CD3(+) population. Protein L bound the majority of the CD19(+) population, but also a fraction of the CD19(-)/CD3 population. Protein M1 was not mitogenic but stained the entire CD19(+) population and 70% of the CD3(+) population. Identical staining patterns were observed with mouse splenocytes using B220 and T-cell receptor as lineage markers. The chimeric protein LG was a potent mitogen for mouse splenic B cells when added either coupled to Sepharose or in soluble form. In addition, protein LG induced differentiation to Ig secretion of the responding mouse splenic B cells. In FAGS analysis, protein LG stained the entire CD19(+) and the majority of the CD19(-)/CD3 lymphocyte population as well as all B220(+) mouse splenocytes and a fraction of the splenic T cells. These data indicate that the bacterial proteins studied interact with surface structures of several leucocyte populations and can hence interfere with the immune system at multiple levels.