Immunoglobulin levels in human colostrum and milk.

The levels of secretory IgA and of IgM and IgG in colostrums and milks obtained at various times postpartum were measured by radial immunodiffusion. Immunoglobulin A was the dominant immunoglobulin in all samples, and concentrations in colostrum ranged from 1.5 to 83.7 g/L (mean 32 g/L). Immunoglobulin M and IgG had mean colostrum concentrations of 1.13 and 0.53 g/L, respectively. Although the levels of each immunoglobulin declined with time postpartum, there was little change in the relative proportion of the immunoglobulin classes present.