Five epitopes of a differentiation antigen on human inducer T cells distinguished by monoclonal antibodies.

A series of mouse monoclonal antibodies reacting with human T cells of the helper/inducer subclass, OKT4, 4A, 4B, 4C, and 4D, have been reported. Using double-fluorescent staining and complement-mediated depletion, it was shown that the antigen(s) recognized by OKT4, 4A, 4B, 4C, and 4D antibodies are present on the same cell. Using FITC-labeled OKT4, 4A, 4B, 4C and 4D, a lack of competition between the antibodies for their epitopes was shown. Immunoprecipitation of the antigen recognized by each antibody yielded a molecule of approximately 60,000-62,000 Da. Sequential precipitation with several antibodies resulted in a minimum of additional precipitated antigen following removal of the first antigen. Capping of cell surface antigen with OKT4, followed by staining with OKT4, 4A, 4B, 4C, or 4D, indicated that the epitopes for all five antibodies co-cap. A sandwich ELISA assay using OKT4 and the other antibodies showed that molecules binding to OKT4A, 4B, 4C, and 4D also bound OKT4. It can therefore be concluded that monoclonal antibodies OKT4, 4A, 4B, 4C, and 4D recognize distinct epitopes present on a molecule of approximately 60-62,000 Da on human helper/inducer T cells.