Increases of IgA milk concentrations correlate with IgA2 increment

IgA, IgA1, and IgA2 concentrations were determined in 81 defatted human mil k samples : colostrum (days 1-5, n = 42), transitional milk (days 6-14, n = 18) and mature milk (days 15-75, n = 21) by immunonephelometry. Correlatio ns were found between total IgA levels and the concentrations of both IgA s ubclasses (p < 0.0001). The levels of the three molecules decreased over la ctation with significant differences (p < 0.05) between colostrum and trans itional milk levels and between colostrum and mature milk. Colostral IgA1 a nd IgA2 mean concentrations dropped respectively from 10.89 +/- 2.12g/L, an d 15.41 +/- 2.10 g/L to 1.83 +/- 0.73g/L and 3.40 +/- 1.25glL in transition al milk reaching finally to 0.36 +/- 0.07 g/L and 0.27 +/- 0.06 g/L in matu re milk. IgA2 concentrations were higher than those of IgA1 when the total IgA level was high. The lgA2 levels in colostrum could be an adaptation res istance of IgA to potentially harmful pathogens able to secrete IgA proteas es and also a way to regulate colonization of the microflora in the newborn . (C) 2001 Wiley-Liss, Inc.