Slow cluster formation of purified human or rhesus T cells requires protein kinasse C and LFA-1

Ab: Homotropic T cell adhesion, as generally studied, consists of a rapid, transient binding process that is measured over a 15-120 min. period. Here we report a slow type of adhesion process occurring with human or rhesus T cells, purified from peripheral blood, that manifests itself by the formation of rounded, multi-layer clusters which may contain hundreds of cells. The maximal number and size of the clusters peak 1-2 days after the addition of phorbol ester, an absolute requirement. The number of clusters formed is proportional to phorbol ester concentration up to 1.25 ng/mL. Phorbol esters such as phorbol myristate acetate (PMA), phorbol dibutyrate (PDB), and 7-octylindolactam (OIL) induced optimal cluster formation at 1-13 ng/mL, levels slightly higher than that required to induce mitogenesis of purified T cells. Phorbol itself and the alpha-form of the ester were inactive. Both cluster formation and mitogenesis (stimulated by Con A or anti-CD3) are completely inhibited by staurosporin at 12.5 ng/mL. Even at 2.5 ng/mL, 74 percent of cluster formation was inhibited, which strongly implies a crucial role for protein kinase C. In the presence of accessory cells, T cell clusters were suppressed. Monoclonal Ab such as anti-CD3, mouse anti-CD3 followed by anti-mouse IgG, anti-CD4, anti-CD4A, anti-CD2, anti-CD8, and anti-CD45 did not induce cluster formation. None were inhibitory or stimulatory in the presence of PMA, except for anti-CD3 which enhanced cluster formation by 26 percent. However, anti-LFA-1 beta-chain (mouse monoclonal) completely blocked cluster formation over the range studied (63-1000 ng/mL) for both human and rhesus cells; rat anti-LFA-1 only blocked human cell adhesion. Anti LFA-1 only partially inhibited T cell mitogenesis. These results show that slow cluster formation shares the LFA-1 and phorbol ester requirements of the rapid adhesion of T cells requiring LFA-1 and ICAM-1. However, cluster occurs at a very low phorbol ester concentration, appears more sensitive to staurosporin inhibition, and is not stimulated via the TCR receptor like the rapid adhesion process. We hypothesize that certain neuronal processes, induced by phorbol ester, and which also show a similar protein kinase C activation time course, may share mechanisms in common with cluster formation

Immunological activities of monoclonal IgG1 antibody against Trypanosoma gambiense.

The present paper deals with the immune reaction between a monoclonal IgG1 antibody and Trypanosoma gambiense. The aggregation of trypanosomes, immune adherence to macrophages and protection against infection are associated with the antibody. IgG1-mediated clumping of trypanosomes is readily dissociated by the addition of complement. Dissociation of the clumped trypanosomes in the equivalence area released approximately fifty percent of previously bound surface antigens. These antigens were capable of binding again to new IgG1 antibody. Complement deposition rendered bivalent IgG1 antibody in the immune complex functionally univalent. Such an event in the presence of complement is of great advantage to the infected host in killing pathogens in vivo, as it allows more antibodies to attach to surface antigens and subsequently to initiate complement activity.