CD4 and susceptibility to pneumonia measurement: When investigating the diversity of the intestinal microbial community between immunocompetent mice and mice depleted of CD4+ T cells, with pneumonia caused by Pneumocystis murina, there was a significant change in alpha and beta diversity and a change in the taxonomic abundance of the intestinal microbiota among these groups, suggesting that the loss of CD4+ T cells affects the intestinal microbiota and the response to P. murina.