Gamma delta T cells are early responders to Mycobacterium avium ssp paratuberculosis in colostrum-replete Holstein calves

Peripheral blood mononuclear cells (PBMC) and mesenteric node lymphocytes (MNL) were obtained from 30 calves that were assigned randomly at birth to 1 of 6 treatment groups with 5 calves per treatment in a 14-d study: (1) colostrum-deprived (CD), no vitamins; (2) colostrum-replacer (CR), no vitamins; (3) CR, vitamin A; (4) CR, vitamin D-3; (5) CR, vitamin E; (6) CR, vitamins A, D-3, E. Calves were injected with appropriate vitamin supplements and fed pasteurized whole milk (CD calves) or fractionated colostrum-replacer (CR calves) at birth. Thereafter, all calves were fed pasteurized whole milk fortified with vitamins according to treatment group. Calves were orally inoculated with 10(8) cfu of Mycobacterium avium ssp. paratuberculosis (MAP) on d 1 and 3. The PBMC and MNL harvested on d 13 were analyzed by flow cytometry as fresh cells, after 3-d culture with phytohemagglutinin (PHA), and after 6-d culture with a whole-cell sonicate of MAP (MPS). Peripheral gamma delta T cells were a predominant lymphocyte subset in neonatal calves, with a decreased percentage noted in CD calves compared with CR calves. As well, CD25 expression was higher in gamma delta T cells compared with other cell subsets, regardless of treatment group. Stimulation of PBMC with PHA resulted in increased CD4(+) and CD8(+) subsets, whereas MNL response was dominated by expansion of B-cell subpopulations. Stimulation with PHA and MPS decreased the relative abundance of PBMC gamma delta T cells, but MNL gamma delta T cells increased upon stimulation with MPS. These results identify gamma delta T cells as key early responders to intracellular infection in neonatal calves and suggest that colostrum may be an important mediator of this response.