T cell responses in calves to a primary Eimeria bovis infection: phenotypical and functional changes

The study aimed to characterize T cell responses in calves to a primary E. bovis infection. For this purpose, peripheral blood lymphocytes (PBL) were isolated from six infected calves and three controls during prepatency (Day 12 post infection (p.i.), patency (Day 25 p.i.) and postpatency (Day 35 p. i.). In addition, lymphocytes were isolated from various lymphatic organs ( lnn. cervicales superficiales, lnn. jejunales craniales, lnn. jejunales cau dales, lnn. caecales, lnn. colici, Peyer's patches (PP) and spleen) at necr opsy (Day 35 p.i.). FACS analyses determined the proportions of CD4(+)-, CD 8(+)-, CD2(+)-, and gamma delta(+)-T cells. Proliferative responses of the cells after stimulation with Concanavalin A (Con A) and an E. bovis-merozoi te I antigen (EbAg) were measured. Furthermore, in situ hybridization exper iments were performed for the detection of IL-2 and IL-4 mRNA in histologic al sections of lymphatic organs. Proportions of CD4(+)-, CD8(+)- and CD2(+) -expressing PBL were significantly increased 12 days p.i. in infected calve s. While the proportions of CD4(+)- and CD8(+)-PBL declined until day 25 p. i. and finally reached control values, proportions of activated PBL (CD2(+) -T cells) remained at a high level throughout the observation period. Those of gamma delta(+)-PBL, in contrast, remained unaffected. The proportions o f CD4(+)-, gamma delta(+)- and CD2(+) - T cells in lymphatic organs were si gnificantly increased in comparison to uninfected controls. when determined 35 days p.i. Concerning the proportions of CD8(+)-T cells of the organs, h owever, there were no differences between the groups. PBL and cells from ly mphatic organs except those from the PP showed strong proliferative respons e to the mitogen Con A, without a significant difference between the groups . Reactions to EbAg in contrast differed significantly between controls and E. bovis infected calves. proliferation responses of PBL of infected anima ls were highest 12 days p.i.; subsequently they decreased and 35 days p.i. they were found within the ranges of controls. Lymphocytes isolated from ly mphatic organs of infected animals reacted significantly stronger than lymp hocytes from control animals, whereby most marked differences occured with cells from lymph nodes draining E. bovis infested parts of the intestine an d from the spleen. These reactions were accompained by an increased transcr iption of the IL-2 gene but not of the IL-4 gene in gut associated lymphnod es of infected calves when compared with infected controls. The data sugges t strong antigenic stimuli by developing first generation schizonts, and of predominant involvement of (CD4(+)) Th1 cells in the course of a primary E . bovis infection of calves. (C)1999 Elsevier Science B.V. All rights reser ved.