Characterization of an immune response gene in rats

Responsiveness to porcine LDH A (a lactic dehydrogenase isoenzyme) in rats is controlled by a dominant gene, Ir‐LDH A , which is linked to the major histocompatibility locus. This gene is unlinked to the gene coding for an allotypic marker on the major class of rat immunoglobulin light chains. Ir‐LDH A controls a specific step in the immune response to the enzyme molecule. The specificity of this step can not be ascribed alone (if at all) to the overall charge of the antigen. High responder lymphocytes retain high responsiveness in a low responder environment. In addition, low responder animals do not appear to contain a material that cross‐reacts with rat anti‐LDH A antibody and that is not present in high responder animals. High, but not low responder lymph node cells could be stimulated by antigen into proliferation in vitro. Low responder animals showed deficiency in developing LDH A ‐specific helper function. These data suggest that Ir‐LDH A is expressed at the level of T cell function.