Human peripheral blood T lymphocytes express alpha-, mu- and F(ab')2-related determinants in their surface membranes.

Whereas a mean of 81% of freshly isolated human T cells bound purified chicken anti-F(ab') antibodies to their surface membranes, 14 and 2% bound chicken anti-μ and chicken anti-α antibody preparations respectively as demonstrated by the mixed antiglobulin rosetting reaction (MARR). Neuraminidase treatment of T cells significantly increased their reactivity in the MARR so that an average of 98, 39 and 40% bound anti-F(ab') anti-μ and anti-α reagents respectively. When using anti-F(ab') antibodies, inclusion of Fabγ in the rosetting medium caused greater than 90% inhibition of the MARR whereas Fcγ produced only 25% inhibition; this indicates that the determinants seen by anti-F(ab') antibodies are not carbohydrate in nature since Fabγ and Fcγ fragments prepared from a human IgG myeloma express identical carbohydrate moieties. To discover whether the various immunoglobulin (Ig) related T cell molecules play a role in antigen recognition, each antiglobulin reagent was assessed for its capacity to inhibit T cell binding of a selected antigen, i.e. fluorescein-labelled keyhole limpet haemocyanin. Whereas the frequency of antigen-binding lymphocytes (ABL) varied from 8·1 to 15·1 per 10 cells, fewer than 1 in 10 cells were Ig-positive with a rabbit F(ab') anti-light chain reagent. Thus virtually all ABL were T cells. Each antiglobulin reagent produced 50% or greater inhibition of antigen binding thereby suggesting that F(ab')-, α-, and μ-related determinants are in close proximity to, or part of, the T cell antigen receptor. More substantial evidence for a direct association of Ig-related surface determinants and the T cell antigen receptor is provided by the finding that under capping conditions, modulation of surface F(ab')-related determinants by anti-F(ab') antibodies reduced antigen binding. Further, that anti-F(ab') antibodies induced F(ab')-, α- and μ-related determinants to co-cap suggests that F(ab')-related determinants are stably associated with α- and/or μ-related determinants in the T cell membrane and are part of the same Ig-related molecule(s).