Variation in T cell responses to ovalbumin in cattle: evidence for Ir gene control.

Genetic control of immune responsiveness in cattle was investigated using an antigen-dependent T cell proliferation assay in vitro. Bovine T cell proliferative responses to ovalbumin were dependent upon major histocompatibility complex (MHC) class II molecules. Responses of an unrelated panel of animals to a limiting concentration of ovalbumin after a single immunization were compared. Two discrete patterns of response were observed. One group of animals had low or non-responses which were not significantly different from the preimmune levels. Another group of animals showed significant responses. After a second immunization the majority of low responders remained low responders. There was no significant correlation between bovine MHC class I BoLA haplotype and magnitude of response within this group of unrelated animals. However, the magnitude of the T cell responses by two half-sib family groups segregated with BoLA haplotypes inherited from the sire. In contrast no significant correlation with antibody responses in vivo could be demonstrated. We suggest that the observed variation in T cell response is linked to bovine MHC class II immune response (Ir) genes.