PROFESSIONAL PRESENTATION OF ANTIGEN BY ACTIVATED HUMAN T-CELLS

Activated human T cells express class II molecules, but their capacity to present soluble antigens and stimulate T cells has been repeatedly questioned. Two lines of evidence indicate that T cells may indeed fu nction as professional antigen-presenting cells. First, T cells that h ave been recently activated can efficiently capture, process and prese nt tetanus toroid to class II-restricted T cell clones. This capacity correlates with the rate of class II synthesis. Second, activated T ce ll clones express high levels of B7, are powerful stimulators in mixed lymphocyte reactions, and their stumulatory capacity is inhibited by soluble CTTLA4 or anti-B7 antibody. Furthermore, expression of B7 can be detected in vivo on T cells from biopsies of patients with liver di sease. Presentation of soluble antigen by activated T cells may play a role in the amplification of the specific response, and possibly in i mmunopathological states.