CD8A and Klebsiella pneumonia: These results suggest that CD4+ and CD8+ T-cells programmed to home to the lung are sequestered in the intestine, impairing lung host defense against Klebsiella. To confirm the importance of T-cells in the defense against Klebsiella pneumonia we depleted CD4+ and CD8+ T-cells prior to respiratory infection with Klebsiella pneumoniae.