T helper cell receptors: idiotypes and repertoire

Idiotopes displayed by T cell receptors could be regulatory elements in the selection and maintenance of the T cell repertoire. Among these, of particular interest are those structures which allow receptor-receptor interactions between distinct T cell clonotypes. The existence of murine T lymphocytes which can be induced to proliferate by a monoclonal antibody specific for an allogeneic Class II antigen has been demonstrated. Such cells can interact with a fraction of the syngeneic T cells which react to the same alloantigen as the antibody. T cells involved in such an interaction were immortalized as IL-2 secreting T hybridomas. Functional and structural data suggest that some T cell idiotopes are internal images of MHC (Class II) epitopes, recognized by both alloreactive T lymphocytes and Ia specific antibodies. The relation between T cell receptor variable gene polymorphism and the predominance of a family of idiotopes indicates, on the other hand, the ability of a V beta gene family to participate in the encoding of receptors which exhibit a variety of antigen specificities. At least in one instance, topochemical resemblance between non-self antigens and self-MHC limits the T cell repertoire and gives rise to Ir gene controlled patterns of T cell responsiveness to nominal antigens.