Importance of competitive binding in the detection of antigen specific bovine isotypes and subisotypes by the micro ELISA.

An enzyme-linked immunosorbent assay was developed to detect and quantify the specific bovine immunoglobulin class response to Trypanosoma theileri, Dictyocaulus viviparus and infectious bovine rhinotracheitis virus. Comparative measurement of the specific immunoglobulin classes in whole serum was achieved using monospecific rabbit antibovine IgG1, IgG2 and IgM, followed by a goat anti-rabbit Ig-enzyme conjugate (antiglobulin ELISA). The results obtained in the antiglobulin ELISA compared favourably with the standard (or indirect) ELISA using the purified immunoglobulins. Competitive inhibition between specific immunoglobulins of different isotypes and subisotypes was the major disadvantage of the antiglobulin ELISA. This latter assay failed to detect specific IgG2 against T theileri antigen in both calf and adult whole serum. The inability to detect the specific IgG2 was a result of competitive inhibition by specific IgG1. However, competitive inhibition between specific immunoglobulins was not observed in either of the other test systems using D viviparus and infectious bovine rhinotracheitis virus antigens.