|Ametaj, Burim - IOWA STATE UNIV., AMES|
|Beitz, Donald - IOWA STATE UNIV., AMES|
Submitted to: International Journal for Vitamin and Nutrition Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 28, 2000
Publication Date: N/A
Interpretive Summary: Immediately after giving birth, the dairy cow is more susceptible to metabolic and infectious diseases. Nutritional and metabolic factors may influence the immune system and resistance to infectious diseases (e.g., mastitis) during this period. Biologically active forms of vitamins A and D, referred to as retinoic acids and 1,25-dihydroxyvitamin D3, can modulate the function of immune cells from cattle. For this reason, there are concerns that supplementing pregnant or recently calved dairy cows with excess amounts of vitamins A and D may affect adversely disease resistance. This study's objective was to evaluate, in vitro, effects of several different forms of retinoic acid individually or in combination with 1,25-dihydroxyvitamin D3 on the capacity of immune cells from nonpregnant heifers and recently calved cows to produce interferon. Interferon, produced by immune cells, is important because it is pivotal in the regulation of immune responses. In general, cells from recently calved cows produced much less interferon than cells from heifers, suggesting that this aspect of immune function is suppressed after calving. Individual forms of retinoic acid did not affect interferon secretion by cells from either group of animals. In both groups, 2 forms of retinoic acid augmented the pronounced inhibition of interferon secretion by 1,25-dihydroxyvitamin D3. These findings suggest that supplementing dairy cows at calving time with high amounts of vitamins A and D may affect a critical function of the dairy cow's immune system. These results will consequently be of great benefit to the dairy industry worldwide.
Technical Abstract: Individual and combined effects of several isomers of retinoic acid (RA) and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] on interferon-gamma (IFN-y) secretion by blood mononuclear leukocytes (MNL) from nulliparous and postparturient Holstein cattle were evaluated in vitro. In the first experiment, effects of incubation period (24-72 h) and time of supplementation (0-32 h) with all-trans, 9-cis-, 13-cis-, and 9,13-dicis- RAs on IFN-y secretion by pokeweed mitogen (PWM)-stimulated MNL from nulliparous heifers were evaluated. In the second experiment, MNL from postparturient cows (bled at 0, 2, 4 and 16 d postpartum) were stimulated with PWM in the presence of RA isomers (9-cis- or 9,13-dicis-RA), 1,25- (OH)2D3, or with combinations of these metabolites. Individual isomers of RA had no effect on IFN-y secretion by PWM-stimulated MNL from nulliparous or postparturient dairy cows. MNL from postparturient dairy cows produced substantially less IFN-y than did MNL from nulliparous heifers. RA individually did not affect the capacity of leukocytes from dairy cattle to secrete IFN-y. This result is in marked contrast to studies in monogastric species, indicating that RAs inhibit IFN-y secretion by peripheral blood T cells. Inhibition of IFN-y secretion by 1,25-(OH)2D3 was potentiated by 9-cis- and 9,13-dicis-RA, suggesting that an excess of dietary vitamins A and D may compromise further the naturally immunosuppressed postparturient dairy cow. Additional research is necessary to determine if the combined effects of these metabolites on IFN-y secretion represent an increased susceptibility of the dairy cow to infectious diseases during the periparturient period.