Clonal analysis of B- and T-cell responses to Ia antigens

Abstract

Thirty-five Ia^k-specific monoclonal alloantibodies, derived from hybridomas constructed by fusion between mouse myeloma and spleen cells from A.TH alloimmune mice (I ^S anti-I ^k ), have been used to estimate the allotypic polyporphism of the I^k-gene products. Cross-blocking studies using 17 mAb specific for the I-A molecule indicated that six determinants, which were associated with the conventional specificities Ia.2 and Ia.19, were organized in at least three distinct polymorphic areas of the I-A^k molecules. Similarly, another group of six determinants, which did not correspond to previously described conventional Ia specificities, were found to be topologically heterogeneous. By contrast, the five epitopes associated with the Ia. 1 specificity were clustered into a single region of this molecule. In addition the potentiation of binding observed between mAb specific for topologically distinct epitope regions of the I-A^k molecule, suggested that the latter may undergo conformational changes after binding of a given mAb. A similar analysis of 17 mAb specific for the I-E^k molecule indicated that specificity Ia. 7 of the E_α chain (as defined in this series by eight mAb) was composed of three topologically distinct polymorphic areas, one of which is also spatially related to a complex cluster of eight new determinants of the I-E^k molecule. Finally, one mAb identified a so far undescribed shared determinant of the I-A^k and I-E^k molecules. The present results, which provide a new estimate of the allotypic polymorphism of the Ia^k antigens, are discussed with regard to their functional, biochemical, and evolutionary implications.