Antigen-specific helper factors in rabbit lack both V and C region Ig determinants

Abstract

THE nature and genetic origin of the T lymphocyte antigen-recognition system is an intriguing and compelling immunological problem. T cells differ from B cells in not synthesising classical antibody and in not expressing a readily detectable immunoglobulin (Ig) as their surface receptor for antigen¹. It has recently been found, however, that in some cases T cells and serum antibody carry the same idiotypic determinants^2–4, inferring identity between the binding sites, that is the variable regions, of the T cell antigen receptor and immunoglobulin. It has also recently been discovered that T cells can produce antigen-specific molecules or factors which carry determinants of the major histocompatibility complex (MHC) in addition to a binding site for antigen^5–8. The existence of the specific T cell factors raises the possibility of variable (V) region genes separate from those contributing to antibody and B cell receptors, and perhaps located in the MHC⁹. In order to resolve these possibilities we have attempted to produce antigen-specific T cell factors in the rabbit. The rabbit is the ideal animal for such a study, since it uniquely carries allotypic markers in the V region of its immunoglobulins (see reviews in refs 10 and 11). The sharing of such a V-region allotypic marker by both Ig and the specific T cell factor would establish a common genetic basis for antigen recognition in the two molecules. The results below show, however, that the Ig V region allotypes determined by the a locus and indeed other Ig markers are not present on the specific T-cell helper factor in the rabbit and imply the existence of separate V genes for antibody and T cell factors.