A unique immune response control locus mapping with the H-2D class I region.

The immune response to the polysaccharide antigen Trinitrophenyl (TNP)-ficoll is controlled by two complementing loci in the murine major histocompatibility complex. One locus of control is present in the I-A subregion and the second is located between the S and D regions. A monoclonal antibody 48-21.7 was selected for its ability to significantly block the in vitro primary response to TNP-ficoll. This antibody bound to antigen-presenting cells does not interfere with the presentation of other antigens. Experiments are presented to demonstrate that the monoclonal antibody 48-21.7 precipitates a unique protein of approximately 40,000 daltons. Sequential immunoprecipitation with monoclonal antibodies to the class I Db antigen and to relevant Ia antigens demonstrated no cross-reactivity. Amino acid sequencing has found unique amino acids to be present at three class I N-terminal invariant positions. These observations indicate the presence of a unique class I-like molecule coded for by genes mapping between S and D and involved in the response to the polysaccharide ficoll.