Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 18, 1997
Publication Date: N/A
Interpretive Summary: When an animal responds to physical or emotional stress, it releases into the body a group of chemicals referred to as corticosteroids. These compounds have been shown in humans and laboratory animals to regulate many aspects of the immune system and, as a consequence, influence responses to inflammation, autoimmunity, and shock. Natural increases in the levels of these compounds are known to occur in dairy cows giving birth and are thought to reduce the responsiveness of the cow's immune system, resulting in increased risk of infection during the period immediately following calving. The present study showed that administration of the man-made corticosteroid, dexamethasone, to healthy Holstein steers caused a dramatic reduction in the functional capacity of immune cells in the blood. These functional changes were associated with alterations in the composition of populations of immune cells in the blood. Overall, these results suggest that corticosteroids can alter negatively the function and composition of the immune cell population in the blood, contributing to the generalized suppression of the immune system observed in dairy cows at the time of calving. This information may be useful in developing strategies to overcome the increased susceptibility of dairy cows to infection at the time of calving. Consumers are eventual beneficiaries of this work, as they are further assured economical and wholesome products.
Technical Abstract: To characterize further the effects of corticosteroid-induced stress on the immune system of dairy cattle, functional and phenotypic characteristics of populations of blood mononuclear leukocytes from control and treated (0.04 mg dexamethasone/kg per d for 3 consecutive d) Holstein bulls were evaluated concurrently. In vivo administration of dexamethasone caused a greater than or equal to 97% reduction in in vitro secretion of interferon-gamma by pokeweed mitogen-stimulated mononuclear leukocytes by d 2 after the first treatment. In vitro secretion of IgM was reduced by more than 50% on d 2 and 3 after the first treatment, but returned to normal sooner than did interferon-gamma secretion. Concurrent with changes in the secretion of these proteins were changes in the mean fluorescence intensities of major histocompatibility class I and II antigens and the WC1 antigen and in the proportion of B cells, CD3 T cells, gamma-delta T cells, and major histocompatibility class II positive cells in the leukocyte population. Examination of the relationships between protein secretion in vitro and the composition of the blood mononuclear leukocyte population indicated that secretion was associated positively with the proportion of CD3 T cells (primarily the gamma-delta T cell subset) and expression of major histocompatibility class I and II molecules and associated negatively with the proportion of major histocompatibility class II positive cells. Overall, these results suggest that corticosteroid-mediated stress in dairy cattle impairs secretion of proteins critical in normal cellular and humoral immune responses, an effect that is strongly linked with changes in the composition of the circulating mononuclear leukocyte population.