Effects of dexamethasone on lymphoid tissue in the gut and thymus of neonatal calves fed with colostrum or milk replacer.

An increased susceptibility to disease in neonatal calves may be attributable to high glucocorticoid levels that influence immune reactions. We tested whether dexamethasone (DEXA) administration influences the proliferation, apoptosis, and number of B- and T-lymphocytes in Peyer's patches (PP) and thymus in calves fed colostrum (C) or a milk-derived formula. All calves were subcutaneously administered bovine colostrum-derived immunoglobulin G and fed chicken-egg derived immunoglobulins that protected against rotavirus and pathogenic Escherichia coli. The DEXA (30 microg/kg of BW daily) was injected for 4 d into groups fed colostrum on the first 3 d (CD+) and those fed the formula that contained nutrients in amounts as in colostrum but no immunoglubulin G (FD+). Groups CD- and FD were fed the same as the other two groups, but did not receive DEXA. Immunohistochemical methods were used to evaluate cell proliferation rates (by labeling of 5-bromo-2'-deoxyuridine), apoptosis rates (by terminal deoxynucleotidyl transferase-mediated X-dUTP nick end labeling). Numbers of T- and B-lymphocytes were determined with antibodies specific for CD3 and CD79 surface proteins. There were significant effects (P < 0.05) of DEXA treatment (decrease of cell proliferation rates in follicles of PP and thymus, increase of apoptotic rate in follicles of PP and thymus, decrease of B-lymphocyte numbers in follicles of PP, increase of B-lymphocyte numbers in domes of PP, increase of T-lymphocyte numbers in follicles of PP, and a decrease of intraepithelial T-lymphocyte numbers). There were significant effects (P < 0.05) of C feeding (decrease of cell proliferation rates in follicles of PP and of B-lymphocyte numbers in interfollicular areas, domes, and follicular-associated epithelium of PP, and an increase of cell proliferation rate in the thymus). A DEXA x feeding interaction (P < 0.001) was found for cell proliferation rate in the thymus. In conclusion, DEXA treatment decreased cell proliferation rates in follicles of PP and thymus and enhanced apoptotic rates in follicles of PP. Colostrum feeding decreased cell proliferation rates, likely of B-lymphocytes, in follicles of PP and numbers of B-lymphocytes in domes, follicular-associated epithelium, and interfollicular areas of PP and enhanced cell proliferation rates and selectively modified DEXA effects in the thymus.