Porcine IgG. Isolation of two IgG-subclasses and anti-IgG class- and subclass-specific antibodies

To investigate the existence of two or more porcine IgG (PIgG) subclasses PIgG was isolated from whey and serum by precipitation with caprylic acid followed by ion-exchange chromatography. Fractions were purified by means of affinity chromatography resulting in the isolation of two products with partly different antigenic determinants. Double immunodiffusion (DI) experiments showed that these products belong to the IgG isotype. Using these products in DI together with antibodies against PIgG class- and subclass-specific determinants it was proven that at least two PIgG subclasses exist (tentatively called IgG1 and IgG2). Quantitation of IgG2 in porcine whey and serum by radial immunodiffusion yielded IgG2 values of 67 and 14 mg/ml, respectively. Probably due to the existence of PIgG1-subpopulations this subclass could not be quantitated reliably. Quantitation of IgG using IgG class-specific antibodies yielded higher IgG values for porcine whey (89 mg/ml) and serum (32 mg/ml) than generally cited in the literature. The possible explanations for these discrepancies are discussed.