An alternative pathway of T-cell activation: a functional role for the 50 kd T11 sheep erythrocyte receptor protein.
Meuer SC., Hussey RE., Fabbi M., Fox D., Acuto O., Fitzgerald KA., Hodgdon JC., Protentis JP., Schlossman SF., Reinherz EL.
A series of seven monoclonal antibodies was produced against the T-lineage-specific 50 kd T11 sheep erythrocyte rosette (SRBC) receptor protein in order to define the function of the molecule. Three distinct epitopes were detected: T11(1), the SRBC binding site expressed on all T lymphocytes and thymocytes; T11(2), an epitope unrelated to the SRBC binding site but with a similar distribution; and T11(3), a neo-epitope expressed only upon T-cell activation. Simultaneous triggering of T11(2) and T11(3) epitopes by monoclonal antibodies induces T lymphocytes to proliferate and mediate their functional programs in the absence of antigen and/or antigen-presenting cells. This antigen-independent mode of triggering is distinct from that involving the T3-Ti antigen receptor complex and represents an alternate pathway of T-cell activation. Given that T11 is the earliest T-lineage surface glycoprotein to appear in thymic ontogeny and is thus expressed before T3-Ti, the former may be involved in clonal expansion and/or differentiation during early development.