The human immunoregulatory T cell circuit: recent progress and its clinical implications.

The present studies indicate that both the heterogeneity and functional programs of human T lymphocytes can be distinguished. Within the T4 subset, which is responsible for inducer/helper functions in T-T, T-B and T-macrophage interactions, discrete subpopulations are present; T4 cells bearing the 2H4 molecule (T4+2H4+) induce T8+ suppressor effector cells, and T4 cells bearing the 4B4 molecule (T4+4B4+) induce help for B cell Ig synthesis. Within the T8 subset are precursors and effector cells responsible for both suppressor or cytotoxic function. It is now evident that T4 cells show a preferential interaction with class II MHC determinants on accessory or target cells, whereas T8 cells have a preference for class I determinants. Furthermore, the T4 and T8 glyco proteins themselves may function as associative recognition structures in such functions. Recent work has elucidated the role of the T3-Ti antigen receptor complex which is involved in both antigen recognition and T cell activation. The T3 molecule, a nonpolymorphic determinant is membrane-associated with the 90KD Ti heterodimer, a highly polymorphic structure with both constant and variable regions, making up the T cell receptor for antigen. It is believed that these unique cell surface glycoproteins will have a critical role in regulating the nature and intensity of the immune response. The clinical relevance of these cell surface glycoproteins in human diseases also will be discussed.