We have developed a novel method for the production and characterization of monoclonal antibodies reactive with lineage-restricted intracellular Ag. Using this technique, we have produced a panel of antibodies that react specifically with permeabilized T lymphocytes but not with permeabilized B lymphocytes or native T cells. One of these antibodies, designated TIA-2, was found to react with greater than 98% of peripheral blood T lymphocytes. Immunoblotting experiments showed TIA-2 to recognize a 32 kd protein that was reduced to 16 kDa in the presence of 2-mercaptoethanol. Immunoprecipitates analyzed on non-reducing/reducing diagonal polyacrylamide gels showed the homodimeric structure recognized by TIA-2 to be associated with additional structures whose pattern closely resembled that of the T cell receptor complex. When immunoprecipitates formed using antibodies reactive with CD3 epsilon were immunoblotted with TIA-2, the homodimeric TCR zeta chain was specifically recognized. Using TIA-2 as a TCR zeta specific reagent, we show that whole cell expression of this TCR subunit is dramatically reduced following exposure to mAb reactive with CD3. mAb reactive with activating epitopes of CD2 were also capable of down-modulating the expression of TCR zeta, but to a lesser degree. Exposure to Con A or IL-2, on the other hand, did not reduce the whole cell expression of TCR zeta. Given the central importance of TCR zeta in the expression of a functionally competent Ag receptor, its reduced expression in response to certain activating stimuli is likely to play an important role in regulating T cell responsiveness.