Bacteria-immunoglobulin-lymphocyte interactions--new aspects.

Of 30 bacterial species tested 18 stimulated DNA synthesis in human blood lymphocytes. The maximum response was after 3-4 days of culture suggesting a mitogenic effect. This was confirmed by the induction of polyclonal antibody production shown by a plaque assay. Most bacterial species increased the DNA synthesis in B-enriched lymphocytes and unseparated lymphocytes but had negligible activity on T-enriched lymphocytes. Among bacteria with a mitogenic effect and ability to induce polyclonal antibody production are Staphylococcus aureus, Haemophilus influenzae, Mycobacterium tuberculosis, Neisseria gonorrhoeae, Streptococcus group A and Streptococcus pneumoniae. In an attempt to define structure (s) on the B-lymphocyte surface responsible for the lymphocyte stimulation the binding of IgD, IgM, and HLA-A, -B and HLA-D antigens to different bacterial species was investigated. A high IgD binding to N. catarrhalis and H. influenzae and a moderate binding of IgD to streptococci was found. Binding studies employing radiolabelled IgD Fab- and Fc-fragments indicated that the binding probably involves the CHl-region of the IgD molecule. Three purified radiolabelled myeloma IgM M-components were all shown to be efficiently bound to many bacteria indicating that a part of the IgM molecule other than the antigen-combining site can be involved in attachment to bacteria. Highly purified detergent-solubilized HLA-A, -B and HLA-D antigens, when separately incorporated into liposomes, were bound efficiently to two strains of N. catarrhalis and to one strain of H. influenzae weakly to one strain of E. coli, but not at all to another strain E. coli. Preliminary experiments indicate that these bacteria-immunoglobulin and bacteria-HLA-antigen interactions lead to lymphocyte stimulation.