Analysis of nondominant idiotypes expressed during alloimmune responses

The antibody response of Lewis rats (RT1.A¹) to class I MHC antigens of the Brown Norway rat (RT1.Aⁿ) was studied. Diversity of the serum alloimmune response was analyzed using syngeneic anti-idiotype raised against monoclonal antibodies of the same specificity. Cross-reactive idiotypes were detected on approximately one in one thousand Lewis anti-RT1.Aⁿ serum antibodies, at concentrations ranging from 20 to 600 ng/ml. The kinetics of idiotype expression coincided with that of total anti-BN antibody production, suggesting that both were regulated by the same mechanism. To determine whether humoral anti-idiotype was involved in such regulation, sera from these animals were screened for anti-idiotype content. Using an RIA sensitive to 20 ng/ml, no humoral anti-idiotype could be detected during any phase of the alloimmune response.