PURIFICATION AND CHARACTERIZATION OF SECRETORY IGA FROM BABOON COLOSTRUM

In this report, we describe a method for purifying secretory immunoglo bulin A (sIgA) from baboon (Papio anubis) colostrum. The colostrum was first clarified by centrifugation and then analyzed with various anti -human Ig-specific immunologic reagents. Cross-reactive IgA in the bab oon colostrum was identified by ELISA. Western blot analysis also demo nstrated cross-reactive epitopes associated with human IgA1, IgA2, sec retory component (SC), and joining (J) chain. To purify the sIgA, colo strum was separated into 4 distinct fractions by gel filtration chroma tography. Analysis of the individual fractions by ELISA indicated that the IgA elutes over one peak. The IgA fraction was compared with puri fied human sIgA on SDS-PAGE, and exhibited heavy (I-I) chains, light ( L) chains, SC, and J chain. The baboon colostrum was also analyzed by ELISA for specific IgG H and L chain epitopes utilizing monoclonal ant ibodies (MAbs). No significant quantity of IgG was detected in the bab oon colostrum or in the individual 4 fractions, while L chain reactivi ty was observed in the sIgA fraction. The sIgA fraction was pooled, co ncentrated, and was found to contain approximately 7 mg/ml sIgA. To de termine if the baboon sIgA was dimeric like human sIgA, the purified s IgA was sized by molecular sieve chromatography. The molecular size of the sIgA preparation (350 kDa) was determined empirically by comparis on to known molecular species used to calibrate the column. In additio n, native SDS-PAGE indicated that baboon sIgA, like human sIgA, migrat es between IgG and IgM, suggesting it has a dimeric form. The purified baboon sIgA preparation should prove useful in the future study of mu cosal immune responses induced in non-human primate species and for th e generation of sIgA-specific immunological reagents.