Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 1998
Publication Date: N/A
Interpretive Summary: The nematode Ostertagia ostertagi is the predominant cause of parasite-induced production losses in cattle throughout temperature regions of the world. This predominance is partially due to the slow and incomplete development of protective immune responses. The present study provides the first definition of cytokine responses of cells taken from animals exhibiting protective immunity to O. Ostertagi. An immunization protocol of 5 drug attenuated infections with O. Ostertagi was necessary to significantly reduce the number of parasites established after experimental challenge. When compared to previously naive animals, immunized animals showed significantly higher helper T-cell ratios than primary infected animals after challenge infections. Conversely, immunized groups showed significantly lower levels of B cells than the previously primary infected animals. These results suggest that T cell mediated immunity plays an important role in protective responses and conversely, enhanced protection might be the result of a decreased polyclonal B cell activation. Decreased levels of interleukin 4 and transforming growth factor-beta1 in protected animals indicated that either lower levels of these cytokines are a reflection of a lower number of worms in the animals or that levels may not be associated with protective mechanisms. These findings represent an important step in identifying the basis for delayed development of protective immunity against this parasite.
Technical Abstract: Cell surface markers and cytokine gene expression of lymphocytes from the local lymph nodes were studied 9 days after primary infection with Ostertagia ostertagi in naive calves or in calves immunized with multiple, chemically attenuated infections. Changes observed in the percentages of lymphoid populations after challenge were similar in animals immunized by either 3 or 5 drug attenuated infections. In both immunized groups, the CD4+/CD8+ ratio was significantly higher than in previously naive animals after challenge infections. Conversely, both immunized groups showed significantly lower levels of Ig-bearing cells than the previously naive animals. No differences were observed in the number of gamma/delta T cells or interleukin 2 receptor (IL-2R) positive cells. After challenge, the levels of IL-4, IL-10, IL-15, interferon-gamma (IFN-g) and transforming growth factor-beta 1 (TGF-B1) were lower in animals immunized by 5 drug attenuated infections, and in the case of IL-4 and TGF-B1, these differences were statistically significant. These results indicate that animals exhibiting protection from reinfection with O. Ostertagi do not show a shift to higher percentages of Ig+ cells characteristic of a primary infection. In addition, protected animals appear to show a decreased IL4 and TGF-B1 response upon challenge when compared to non-immune animals.