LYMPHOCYTE POPULATIONS AND IMMUNE-RESPONSES IN CDS-DEFICIENT MICE

The CD5 antigen is expressed at a high level on T cells from early on in thymocyte ontogeny and continues to be expressed on the surface of all mature T cells. In addition, it marks a population of B lymphocyte s (B-1a) with distinct physiological properties. To study the in vivo function of CD5, the murine gene was inactivated using the technique o f homologous recombination in embryonic stem cells. In homozygous muta nt mice the CD5 antigen is not expressed on the surface of either T or B lineage cells, indicating that in both cell populations this antige n is encoded by the same gene. CD5-deficient (CD5T) mice are healthy a nd populations of T and B lymphocytes in these mice look unchanged whe n compared to control mice. The mutant mice are able to mount effectiv e immune responses to T cell-dependent and -independent antigens.