Abstract
The lymph node cells from 11 strains of rats, differing in the genotype of the major histocompatibility complex of the rat (RT1), were examined on the basis of their proliferative response to the cell wall antigen of Streptococcus mutans. The 11 rat strains fell into three groups: high, intermediate, and low responders. To demonstrate the influence of the major histocompatibility complex on immune responsiveness to S. mutans, further experiments were performed using the RT1-congenic rat strains WKAH.1L(LEW), WKAH. 1AV1(ACI), and WKAH.1J(LEJ), which differ only in the genotype of the RT1 region. Although the background genes of each strain were of WKAH origin, WKAH.1L(LEW) and WKAH.1AV1(ACI) rats showed a low response whereas WKAH.1J(LEJ) rats showed a moderate response to the S. mutans cell wall antigen. The results indicate that the immune response is controlled by the class II gene(s) in RT1. Furthermore, the RT1.D locus products were shown to play an important role in the restriction molecule, since a monoclonal antibody, HOK7, directed to the RT1.Dk locus products reduced the proliferative response of lymph node cells.