B cell response to schistosome antigens in adult Males occupationally exposed to s. Manson In Western Kenya

Abstract

Increasing levels of membrane CD23 (CD23) on B cells and soluble CD23 (sCD23) in plasma are related to development of resistance to re-infection with: Schistosoma mansoni. However, the mechanisms underlying CD23 expression on B cells remains less understood. In this study, in vitro B cell response to crude schistosome antigen stimulation as well as sCD23 and IgE levels in plasma and culture supernatants from S. mansoni exposed male adults were investigated. Blood was obtained from 34 adult males occupationally exposed as car washers or sand harvesters along the shores of Lake Victoria in Kisumu. Peripheral blood mononuclear cells (PBMCs) were isolated from heparinized fresh blood and B cells were obtained from the PBMCs by negative selection using magnetic bead separation. B cells were cultured at approximately 20xl06 cells/mL for 5 days in RPMI-1640 alone or with soluble egg antigen (SEA), soluble worm antigen preparation (SWAP), recombinant IL-4 (rIL-4) and anti-CD40 mAb (each alone, and, the first two in combination with one or both of the third and fourth). To determine whether B cells respond differently in pureculture or in PBMC, some 7 PBMC cultures were stimulated under similar conditions with pokeweed mitogen (PWM), anti-IgE mAbs, SWAP, SEA, or phytohaemagglutinin (PHA). B cell expression of membrane-bound CD23 was determined by flow cytometry using FACSCalibur (Becton Dickinson) while the quantitative release of sCD23, and IgE in cell-free culture supernatants and plasma were measured by direct ELISA. Flow cytometry data was analyzed on FlowJo (Treestar, 2008) . .Regression, correlation and ANOV A analyses were done using GraphPad Prism software v. 5. Both CD23 expression on B cells and sCD23 release into culture supernatants were .significantly raised in the presence of SEA, rIL-4 and anti-CD40 mAb. The expression of CD23 on B cells was inversely proportional to sCD23 levels, directly related to IgE levels but unrelated to S. mansoni egg counts in stool, but these observations were not statistically significant (p>0.05). The factors involved in CD23 cleavage from cell surfaces and further breakdown remain unclear and warrants detailed studies that involve biochemical and molecular analyses.