Preferential transport into colostrum of Fc fragment derived from serum IgG1 immunoglobulin in the goat.

The selective transport of blood IgG1 into colostrum in ruminant species is not well understood. Therefore, the transport of Fc fragments isolated from serum IgG1 (Fc gamma 1) and IgG2 (Fc gamma 2) in normal and pregnant goats was studied. The animals were injected intravenously with radio-labelled 125I-Fcgamma1 and 131I-Fcgamma2 fragments. The plasma disappearance rate of both fragments showed that at parturition the Fcgamma1 fragment had a higher disappearance rate than Fcgamma2. Over 70 per cent of the inoculated dose of 125I-Fcgamma1 and only 11-12 per cent of 131I-Fcgamma2 could be recovered in the 24 h colostrum. The results indicated that structural differences between the H chains of IgG1 and IgG2 were implicated in the selective transport of IgG1 into colostrum in ruminants.