Immunoglobulin isotypes of lactating Holstein cows classified as high, average, and low type-1 or -2 immune responders.

Infectious diseases are detrimental to the health and economy of the livestock industry. Observations of cattle resistant to natural infections have implied the feasibility of breeding livestock for disease resistance. Studies of pigs selected for antibody (AMIR)- and cell (CMIR)-mediated immune responses have demonstrated increased immune responsiveness suggesting enhanced protection by both type 2 and type 1 responses, respectively. Additionally, natural or artificial infections of cattle suggest that the production of particular immunoglobulin (Ig) M, IgG1 and IgG2 isotypes are important for protecting against pathogens. In fact, IgG1/IgG2 ratios are often used to establish whether type 1 (CMIR) or type 2 (AMIR) responses predominate following immunization or infection. The objectives of this study were therefore; (1) to evaluate the Ig isotype bias responses to Candida albicans and hen-egg white lysozyme (HEWL) in cows classified as high responders (HR), average responders (AR) or low responders (LR) based on AMIR or CMIR; (2) to determine if ranking based on IFN-γ (a type 1 cytokine) and DTH responses were analogous in terms of ranking; and (3) to estimate IFN-γ, Ig isotypes, and DTH correlations. Antibody responses to HEWL and DTH to C. albicans were detected such that cows were phenotypically classified as HR, AR and LR for AMIR or CMIR with significant differences (p ≤ 0.05) among classified groups. C. albicans-induced IFN-γ allowed classification of cows, some of which had the same ranking as that of DTH response. The lowest IgG1/IgG2 ratio was to the C. albicans purified antigen (candin), but no differences were observed in anti-HEWL or anti-candin IgG1/IgG2 ratios between classified groups. Anti-HEWL IgG1 and IgG2 responses at day 21 post-immunization were negatively and significantly correlated with DTH to candin at 24h. There were no significant correlations between anti-HEWL or anti-candin IgG1 or IgG2 responses with IFN-γ. Based on Ig isotype bias, IFN-γ and DTH responses, it was concluded that immunization with C. albicans can be used to classify CMIR responder cows based on DTH read-out.