Genetic selection for high and low immune response in pigs: effects on immunoglobulin isotype expression.

Immunoglobulin (Ig) function varies by isotype and antibody activity is best mediated by isotypes most able to control the inciting infection. In pigs, a high ratio of IgG1:IgG2 is associated with resistance to disease caused by the extra-cellular bacterium Actinobacillus pleuropneumoniae. This ratio is controlled by type 1/type 2 cytokines in vitro, reflecting cell- (CMI) or antibody-mediated immune (AMI) responses, respectively. Animals were used which had been previously selectively bred for high (HIR) or low (LIR) combined AMI and CMI and had been immunized with hen eggwhite lysozyme (HEWL) in Quil A (days 0 and 14) while Bacillus Calmette Guérin was given on day 9. To test the hypothesis that lines do not differ in IgG isotype expression as antibody to HEWL, the ratio of anti-HEWL associated with IgG1 and IgG2 was determined at days 0, 9, 14 and 21. The ratio of IgG1:IgG2-associated antibody was always <1.0 indicating a type 1 response and differed significantly over time in HIR and LIR animals. After primary and secondary immunizations, the HIR animals' IgG1:IgG2-associated antibody ratio increased and approached 1 while for LIR animals the ratio decreased. Thus anti-HEWL antibody in HIR, but not LIR, approached balance in type 2:type 1 expression. Individual variation in immune response was frequently significant within each immune response group. Thus, proportional production of anti-HEWL antibody associated with IgG isotypes varies by individual and differs over time as a function of genotype in pigs selectively bred for HIR or LIR.