Schistosoma mansoni: the host immune response to egg antigens. I. Partial characterization of cellular and humoral responses to pI fractions of soluble egg antigens.

Soluble egg Ag (SEA) were separated according to charge by agarose-IEF (A-IEF) in order to partially characterize those antigenic determinants that may elicit the granulomatous response in schistosomiasis mansoni. Coomassie blue-stained A-IEF gels of SEA showed that this technique was able to resolve multiple isobands. A-IEF gels were sliced into 18 or 36 fractions from anode to cathode, and the SEA components from the isoelectric point (pI) fractions were eluted from gels in a manner that allowed for their direct utilization in both cellular and in humoral immunoassays. Only Ag in two distinct pI ranges consistently elicited lymphoproliferative responses, with the major stimulatory fractions being in the acid (3.5 to 5.0) range. Lymphocytes from mice infected for 10 wk had higher proliferative responses to both SEA and fractionated Ag in this acid pI range when compared to lymphocytes from mice infected for 25 wk; however, the latter had an enhanced response to Ag with a pI range of 6.2 to 6.4. In contrast to the cellular responses, the corresponding sera from these mice, or from schistosome-infected patients, recognized Ag in all pI fractions as determined by ELISA. However, although protective and nonprotective mAb (which recognize an egg Ag that cross-reacts with a 38-kDa schistosomular Ag) bound to most acidic fractions, only the nonprotective mAb (which also recognize determinants on keyhole limpet hemocyanin), bound, in addition, to fractions in the basic range. Finally, the m.w. of Ag in the various pI fractions were determined by SDS-PAGE analysis.