The purpose of the research outlined in this proposal is to examine the fine structure of the chromosomal region which encodes variable regions of immunoglobulin heavy chains. Monoclonal antibodies (Mab's) against individual rabbit VH allotypic specificities will be made in mouse-mouse lymphocyte hybridomas. Individual Mab's and mixtures of these Mab's will be reacted in a quantitative radioprecipitation assay against rabbit IgG to identify subpopulations of the VHa allotypes. Each of the VH sub-populations identified in individual rabbits will presumably reflect a different VH germ lines gene. The molecular and cellular distribution of the various subpopulatins will be examined in each of several rabbits; we will particularly look for VH a subpopulations which are found in some but not all rabbits of that particular VH a allotype. The distribution of the VH a subpopulations in IgA "recombinant" molecules will also be determined. Other studies will be to test for cross-reaction of anti-al Mab's with IgG of the a2 and a3 allotype as well as with human IgG. These cross-reactions should shed light on the evolution of VH genes. Attempts will be made to prepare MAb to the allelic products of the VH genes x32 and y33 i.e., x minus and y minus.