IS THE ESTABLISHING OF TOLERANCE TO SELF OBLIGATORILY MHC RESTRICTED

The prevailing paradigm used to interpret how T cells recognize antigen treats antigen processing as obligatory because the T cell antigen receptor complex can only detect antigen located in a "groove" found on MHC-encoded restricting elements. The vast majority of experimental systems used to analyze how T cells recognize antigen depend on induced T cells executing their effector functions, and it is agreed without exception that this event is MHC restricted. However, to date, the extrapolation of the obligatory MHC restriction of effector function to the level of the antigen-responsive T cell that makes the tolerance induction decision, depends not on experiment, but on theoretical constructs. The few experiments designed to test whether tolerance is MHC restricted are open to several interpretations, only one of which is consistent with the view that all antigen recognition events must be MHC restricted. If it can be shown that tolerance is not obligatorily MHC restricted, then the pillar of the prevailing paradigm will have fallen. The experiments described here throw into serious doubt the evidence that has been used to conclude that tolerance is obligatorily MHC restricted.