Antibody avidity in Yorkshire pigs of high and low immune response groups

Avidity indices of antibody to hen egg-white lysozyme (HEWL) were measured by chaotropic ion (SCN-) elution enzyme-linked immunosorbent assay (ELISA) in pigs grouped as high, control or low for various immune and innate resistance-related traits. The avidity index was the molar concentration of SCN- required to reduce by 50% the ELISA optical density value for a given serum. The index was independent of the amount of antibody. Eight- to ten-week-old Yorkshire pigs were immunized with HEWL and serum antibody measured by ELISA as one of five traits used to assign them to high, low or control response groups. Serum antibody avidity for HEWL was evaluated on Day 14 and Day 30 after primary (Day 0) and secondary (Day 14) immunization. The effects of response group, gender, litter, serum IgG concentration and anti-HEWL antibody on avidity were determined using a linear model. Antibody avidity indices varied amongst individuals. Mean avidity indices for sera collected on Days 14 and 30 were 0.61 +/- 0.43 and 1.22 +/- 0.56, with maximum indices of 2.64 and 2.86 respectively. Avidity of secondary response antibody was significantly higher (P less than or equal to 0.05). Pigs of the high response group had significantly higher secondary antibody avidity than those of the control (P less than or equal to 0.08) and low groups (P less than or equal to 0.01). Avidity index was positively correlated with antibody to HEWL on Days 14 and 30 but not to preimmunization serum IgG concentration or to other measured traits.