A monoclonal antibody (VEP10) against an antigen shared by human large granular lymphocytes, thymocytes and activated T cells.

In an attempt to produce monoclonal antibodies against human large granular lymphocytes (LGL), the effector cells of natural killer (NK) and killer (K) activity, a monoclonal IgM antibody (VEP10) has been obtained. This antibody is reactive by indirect membrane immunofluorescence (IMF) with 14.7 +/- 8.5% peripheral blood lymphocytes (PBL), with greater than 95% thymocytes and with 25.0 +/- 5.0% bone marrow (BM) cells; a stronger expression of VEP10 antigen was found on thymocytes than on PBL and BM cells. Compared to unseparated lymphocytes a higher percentage (58.5 +/- 10.2) of VEP10+ cells could be detected in LGL-enriched cell preparations obtained by Percoll gradient centrifugation. Evidence that the VEP10 antigen is expressed on NK and K cells was provided by depletion of NK/K activity by antibody plus complement treatment of PBL. In addition, VEP10 antigen could be detected on certain human cell lines (Raji, Daudi, Molt4, Yurkat, KG1). The expression of VEP10 antigen on leucocytes could be increased by interferon-alpha treatment and was also observed on concanavalin A (Con A)- and phytohaemagglutinin (PHA)-activated cells. The IMF distribution of VEP10 antigen on various cell types and successful blocking experiments with OKT10 revealed that both antibodies seem to recognize the same or closely related epitopes on cell membranes. In addition to IMF, a more sensitive assay, rosette formation with VEP10-coated ox red blood cells, was employed to study VEP10 antigen expression on cells. Rosette formation experiments indicate that this antigen is also present although in lower amounts on IMF-negative cells, e.g. most T, B cells and monocytes. The finding that the expression of the VEP10 antigen increases under the influence of the thymic environment, mitogens or interferon suggests that VEP10 antibody recognizes a molecule involved in the proliferation and differentiation of haemopoietic cells.