This microscopic image captures a few villi from the small intestinal mucosa of a calf, and two subsets of T lymphocytes are demonstrated with green and orange immunofluorescent labeling of membrane proteins. The T lymphocyte subsets in this image are concentrated within and subjacent to the epithelium, and these cells play a vital role in host immune defenses and intestinal homeostasis. This image was captured as part of a study investigating intestinal T cell responses during early experimental Mycobacterium avium subspecies paratuberculosis (Map) infection of calves. Persistent sub-clinical Map infection in ruminant species inevitably progresses to clinical disease, known as Johne’s disease, which is characterized by malabsorptive diarrhea, wasting, and eventual death.