Preferential mammary storage and secretion of immunoglobulin gamma (IgG) subclasses in swine

Levels of three immunoglobulin gamma (IgG) subclasses, IgGA, IgGB and IgGC, were measured in sow sera, mammary glands, colostrum and milk samples by the single radial immunodiffusion. Serum IgGA and IgGB levels, but not IgGC, showed time dependent variations during gestation and lactation periods. The IgGA level started to decline at day 106 of gestation, reached its minimum at farrowing, and returned to the pre-gestation level 1-3 weeks after weaning. The serum IgGB level started to decrease at day 111 of gestation, reached its minimum at farrowing, and returned to the initial gestation level 1 week after farrowing. A notable decrease (P less than 0.1) in serum IgGC level was observed only on the day of farrowing. IgGA and IgGB were preferentially stored in mammary glands of full-term pregnant sows and secreted into colostrum after farrowing. In contrast, relatively small amounts of IgGC were stored in the mammary glands and secreted into colostrum. These data are interpreted as an indication that the preferential storage of IgGA and IgGB in the mammary gland of sows occurs at the time of significant decreases of these two IgG subclasses in the sera during late gestation and early lactation.