The T-cell receptor mediating restrictive recognition of antigen.
Four facts characterize restrictive recognition of antigen. First, in large measure, allele-specific determinants on R are recognized when R is functioning either as a restricting element (RL) or as an allo-target (or even xeno-target) (RF). Second, there is a high frequency of virgin antigen-responsive t cells with alloreactivity, i.e. anti-RF. Third, there is a strict relationship between the class of effector function and the class of RL recognized (restrictive recognition of antigen, XF) but a relaxed relationship between class of effector function and class of RF recognized (alloreactivity). Fourth, the effector T cell functions anti-RL-dependently when XF is the target (restrictive recognition of antigen) and anti-RL-independently when RF is the target (alloreactivity). From these facts are derived the following conclusions. The T cell uses a dual recognitive, single receptor (Model I, Figure 1). A single germ-line VT locus specifying anti-allele-specific recognition of species R encodes both the anti-R and the anti-X combining sites. A "learning" process (occurring in the thymus) is required to establish the restriction specificity (anti-RL) as well as the effector function/class of RL relationship. The repertoire is derived by somatic mutation of all germ-line VT genes specifying anti-RF (Model IA, Table 3 and Figure 9). Given Model IA (Table 3 and Figure 9), we can account further for the existence of an extensive polymorphism of R and minimal polygeneism, for the high frequency of crossreactivity between anti-XF and RF, and for the physiology and genetics of cell-cell communication in immune responsiveness.