CD5DIM PERIPHERAL-BLOOD LYMPHOCYTES PROLIFERATE TO EXOGENOUS IL-2 IN THE ABSENCE OF ANTIGEN AND KILL IN AN NK-LIKE MANNER

Bovine CD5 lymphocytes can be categorized into "bright" and "dim" populations on the basis of CD5-specific monoclonal antibody (mAb) binding. CD5dim lymphocytes enriched by negative selection using mAbs to CD2 and MHC class II were examined phenotypically and functionally. CD5dim-enriched lymphocytes were 50-74% T19+ and 5-36% CD8+. Fewer than 13% expressed CD4, IgM, or MHC class II on their surface and 6-20% expressed low levels of CD2. These cells did not proliferate to alloantigen or uv-inactivated BHV-1, but did proliferate to Con A and IL-2 in the absence of antigenic or mitogenic stimulation. Following IL-2 stimulation, the T19+ CD5dim lymphocytes proliferated and CD11c expression was induced. Freshly isolated CD5dim lymphocytes failed to kill in a bovine NK-like assay; however, following culture CD5dim-enriched lymphocytes exhibited non-MHC restricted cytotoxicity. We suggest that the CD5dim-enriched lymphocyte population contains the precursors of bovine LAK killing; however, a more extensive phenotype of these precursors in the bovine is yet to be determined. © 1990.