Characterization of protective immune responses in local lymphoid tissues after drug-attenuated infections with Ostertagia ostertagi in calves

In the present study, cell-surface markers and cytokine gene expression of lymphocytes from the local lymph nodes were studied 9 days after primary in fection with Ostertagia ostertagi in previously naive calves or in calves p reviously immunized with multiple, chemically attenuated infections. Change s in lymphocyte populations were assessed by Bow cytometry utilizing monocl onal antibodies specific for bovine cell-surface markers. Changes observed in the percentages of lymphoid populations after challenge were similar in animals immunized by either three or five drug-attenuated infections. In bo th immunized groups, the CD4(+)/CD8(+) ratio was significantly higher than in naive animals after challenge infections. In addition, both immunized gr oups showed significantly lower levels of Ig-bearing cells upon experimenta l challenge when compared to animals with a primary experimental infection. No differences were observed in the number of gamma delta or interleukin 2 receptor (IL-2R) positive cells. The levels of mRNA for IL-4, IL-10, IL-15 , IFN-gamma and TGF-beta 1 were examined by competitive RT-PCR. After chall enge, the levels of these cytokines were lower in animals immunized by five drug-attenuated infections, and in the case of IL-4 and TGF-beta 1, these differences were statistically significant. These results indicate that ani mals exhibiting protection from reinfection with O. ostertagi do not show a shift to higher percentages of Ig(+) cells characteristic of a primary inf ection. In addition, protected animals appear to show a decreased IIA and T GF-beta 1 response upon challenge when compared to non-immune animals. Publ ished by Elsevier Science B.V.