Cell cycle-dependent expression of antigen-binding and I-J-bearing molecules on suppressor T cell hybridomas.

The I-J and antigen-binding chains with constant region determinant (Ct) that compose an antigen-specific suppressor T cell factor were found on the surface of suppressor T cell hybridomas, serologically and morphologically demonstrated by a fluorescence-activated cell sorter (FACS) and immunoelectron microscopic analyses. Moreover, the surface expression of the I-J and Ct-bearing chains fluctuating with the same kinetics depended entirely upon the cell cycle. The maximum expression of these two chains was observed in the early stage of the M phase, and the minimum in the S phase. Similarly, the magnitude of the suppressor activity was maximal in the late stage of the M phase, and was minimal in the S phase. The results therefore demonstrated that there exists good correlation between the cell surface expression of the I-J and Ct-bearing chains and the magnitude of the suppressor activity produced. The antigen recognition units on suppressor T cell hybridomas have serologically and morphologically been characterized by using radiolabeled antigens or monoclonal antibodies against the I-J or Ct on the antigen-binding molecule. Cell-binding assay and radioautographic analysis demonstrated that the suppressor T cell hybridoma possesses the capacity to bind native antigen in an antigen-specific fashion as does the hybridoma-derived, antigen-specific suppressor factor composed of the I-J and the Ct-bearing chains, indicating that the recognition unit on the cell surface is composed of a structure similar to the factor.