Highly purified murine lymph node T cells were used to test the hypothesis that polyclonal T cell activation requires the recognition of mitogen-modified major histocompatibility complex (MHC) antigens on accessory cells (AC) by the T cells. A veriety of tumor cell lines, including macrophage, B and mast cell tumors, as well as thymomas, were shown to function as AC in concanavalin A-induced T cell activation, even if they expressed only one class of MHC antigens or none at all. In contrast to antigen-specific responses, where the Lyt-2+ phenotype is reportedly associated with recognition of class I MHC antigens, T cells enriched for or depleted of Lyt-2+ cells were not preferentially activated in the presence of class I- or class II-positive AC, respectively.
In addition, as shown by others in the guinea pig and in the rat systems, T cell proliferation induced by oxidation of cell surface sugars is equally effective if T cells or AC are oxidized. T cell mitogens, therefore, do not seem to act by altering MHC antigens on AC, but rather by providing T cell-AC contact via their agglutinating properties.