A novel lymphocyte activation antigen present on allospecific primed lymphocytes and defined by the monoclonal...

This study describes VG01, a monoclonal antibody to a novel lymphocyte activation antigen. The cells reacting with VG01 were first characterized by indirect immunofluorescence and fluorescence-activated cell sorter analysis. The antigen defined by VG01 was expressed on circulating T lymphocytes (23.8 +/- 9.0) and on the majority of large granular lymphocytes and monocytes (greater than 90%), while granulocytes stained weakly. All other cells tested so far--thymocytes, hematological malignancies and several cell lines--were negative. Upon activation with mitogens or allogeneic cells more than 90% of the transformed lymphocytes became VG01-positive. The kinetic studies demonstrated that the antigen defined by VG01 lags the expression of the IL-2 receptor by 48 hr and remains present for up to 18 days after stimulation in culture. Thus, this antigen does not seem to be involved in the initial steps of T cell activation and its expression continues after cell division has stopped. Assays with purified sorted populations showed that lymphocyte proliferation to mitogens and in mixed lymphocyte culture came primarily from the VG01- population. The responding cells became VG01+ during activation--and when alloantigen-primed lymphocytes were sorted and restimulated with the original stimulators, all the in vitro memory response came from the VG01+ population. Thus, VG01 antibody is efficient in selecting for alloreactive T lymphocytes in vitro and has potential for selective modulation of immune responses. Its reactivity with activated T cells and NK cells may also help define a common functional program for these two cell types, adding to the understanding of their mechanism of action and/or their origin.