The PMA-induced specific association of LFA-1 and talin in intact cloned T helper cells

Previous experiments with individual cell couples formed between cloned T helper (Th) cells and antigen-presenting cells have led us to suggest that the cytoskeletal protein talin may be associated with the cell surface protein LFA-1 in the Th cell. In order to examine this suggestion, we induced the surface capping of LFA-1 with suitable specific antibody reagents on the intact Th cells, and then determined by double immunofluorescence microscopic experiments, whether talin was co-clustered with the LFA-1 caps. With untreated Th cells, capping of LFA-1 did not result in any redistribution of intracellular talin. However, if the intact Th cells were treated with the phorbol ester PMA, the capping of LFA-1 resulted in a co-clustering of talin with the LFA-1 caps, but not a alpha-actinin. The capping of TCR or CD4 on the Th cells with or without pretreatment with PMA did not lead to any such co-clustering of talin with these caps. PMA treatment of the Th cells therefore induces a direct or indirect association of talin with LFA-1 underneath the Th cell surface. PMA treatment of the Th cells also increased their polarized spreading and adherence to substrata, as had been observed before. We found, furthermore, that this increased adherence upon PMA-treatment was inhibited by the presence of antibodies to LFA-1. The association of talin, and very likely also F-actin microfilaments, with LFA-1 appears to mediate a generalized increased adhesivity of the Th cells. The relevance of these findings with isolated Th cells to the interaction of Th cells with specific antigen-presenting cells is discussed.