CD8A and infection: Furthermore, the differences observed in CD3+CD8+ T cells suggest that cytotoxic CD8+ T cells could be engaged in mounting an immune response to Leptospira. Interestingly, in cattle vaccinated with a Leptospira bacterin and subsequently challenged with L. borgpetersenii serovar Hardjo, CD8+ were the only T cells that proliferated 6 weeks post infection (22).