Role of antigen and bacterial infection in the expansion of H-Y male CD8^lo cells in vivo. Purified CD8^hi and CD8^lo cells were labeled with CFSE and injected into the indicated nonirradiated Thy1.1 congenic B6 male or female mice. The mice were then infected with LM (right panels) or left uninfected (left panels). On day 5, the expansion of labeled CD8^hi and CD8^lo cells in the spleens of infected or uninfected mice was analyzed by FACS. The numbers in the histograms represent the percentage of undivided cells.