INDUCTION OF COGNATE AND NONCOGNATE T-CELL HELP FOR B-CELL IGE PRODUCTION IN RELATION TO CD40 LIGAND EXPRESSION

Nonactivated, fixed peripheral blood T cells (PET) from healthy donors or patients with X-linked-hyper-IgM (HIGM) syndrome, or cloned T cell s provided effective help for tonsillar B lymphocytes for induction of IgE or other immunoglobulin (Ig) isotypes, Helper activity was mediat ed by staphylococcal superantigens adsorbed to the T cells prior to fi xation and required presence of IL-4 in the cultures. We demonstrated that the T cells neither expressed detectable CD40 ligand at the begin ning of the superantigen treatment nor 24 h later, Phorbol ester (PMA) plus Ca-ionophore treatment efficiently induced CD40L, Such T cells d id not, however, provide any help for B-cell activation in some experi ments or stimulated only low responses in others. Antibodies against C D2, CD3 and ICAM-1 adsorbed to fixed T cells prior to coculturing inhi bited helper activity. A soluble CTLA4 construct was also inhibitory, Our results suggest a pathway of B-cell activation independent of CD40 L expressed on T cells.