LFA-1-dependent OKT3-driven T cell clusters in common variable immunodeficiency

SUMMARY The triggering of the TCR/CD3 complex by anti-CD3 (OKT3) antibody leads to the formation of T cell clusters. In cultures of T lymphocytes from most normal individuals, the peak of cluster formation occurs at 24 h. but with cells from patients with common variable immunodeficiency (CVI) it was seen earlier al 4–9 h; in addition, the clusters were larger than normal, particularly at 9 h. Cluster formation by CVI and normal cells was dependent on temperature and divalent cations, but did not require Fc receptors. Since OKT3 clustering is known to be dependent on the LFA-l/ICAM-l adhesion system, the effect of monoclonal antibodies directed against these molecules was tested. A potent inhibitor was the antibody against the common beta chain of the integrin family (CD 18). But of four MoAbs against the alpha chains (CD 11), three inhibited and one stimulated T cell aggregate formation. Increased expression of LFA-I or ICAM-1 on CVI patients'T cells could not be demonstrated. The accelerated clustering was therefore probably due lo an increase in the proportion of cells carrying the activated form of LFA-1. The formation of large numbers of homotypic lymphocyte clusters might reduce the effective interaction between Band T cells, thus contributing to the depression of immunoglobulin synthesis observed in this disease.