Kinetics of expression of T-cell "activation" antigens on in vivo- and in vitro-stimulated T cells.

The in vivo expression of T-cell activation antigens defined by means of an OKT series of monoclonal antibodies and the anti-Tac antibody was evaluated in peripheral T lymphocytes obtained from patients with infectious mononucleosis and in cerebrospinal fluid (CSF) cells collected from individuals with mumps meningitis by the immunoperoxidase method. Although Tac antigen was definitely expressed on about 10% of CSF cells in mumps meningitis, Tac+ T cells could not be identified on any peripheral blood T cells in infectious mononucleosis, which expressed OKIa 1+, OKT10+, and OKT9+ determinants, as a probable sign of in vivo activation. The coexpression of Ia+ antigens on a T-cell functional subset might be important for their functional properties. Our kinetic study and cell cycle analysis of the expression of these activation antigens suggested that Tac antigen might be expressed at the early stage of the G1 phase of the cell cycle; OKT9+ antigen at the late stage of the G1; and Ia+ and OKT10+ determinants might be expressed at the S phase or later on in vitro, probably one after another.