Inhibition of murine B cell proliferation and down-regulation of protein kinase C levels by a phosphorylcholine-containing filarial excretory-secretory product.

E-S 62, a major excretory-secretory product of the rodent filarial parasite, Acanthocheilonema viteae, inhibits the polyclonal activation (DNA synthesis) of mouse B cells by mitogenic anti-Ig antibodies. This effect appears to be due at least in part to the phosphorylcholine (PC) moiety of the molecule, because it can be mimicked by PC-BSA or PC-chloride. Activation of the B cells by LPS is not influenced by the presence of E-S 62/PC, suggesting that they may target some aspect of signaling via the Ag receptor. E-S 62/PC failed to inhibit surface Ig-mediated generation of the second messenger, inositol triphosphate, indicating that their target may not be the early biochemical events associated with activation. Exposure to E-S 62/PC was found to lead to a reduction in the level of protein kinase C, an important downstream regulatory enzyme, in anti-Ig-treated cells. This protein-kinase C down-regulation may be the biochemical mechanism underlying E-S 62/PC-mediated inhibition of surface Ig-activated B cells.