The polyclonal activation of lymphocytes and T cell mitogenicity by a unique sialic-acid-binding lectin from the hemolymph of Achatina fulica snail

Abstract

A unique sialic-acid-binding lectin, Achatinin_H, isolated from the hemolymph of Achatina fulica snail was found to be strongly mitogenic, as monitored by [³H]thymidine incorporation assay, to rat and human lymphocytes. However, the degree of mitogenic response varied with the type of cell population. As indicated, this lectin induced proliferation of purified T lymphocytes and rat thymocytes, whereas it was less mitogenic towards peripheral lymphocytes of pregnant rats and was not mitogenic towards B lymphocytes. Furthermore, the mitogenic response was inhibited by the sialic-acid-containing disaccharide, a strong inhibitor of this lectin. This suggests that lymphocyte cell surface molecules containing sialic acid residues are important for this interaction and may have a structure similar to that of Achatinin_H receptors. Although this lectin showed strong mitogenicity towards lymphocytes, it showed very weak leucoagglutination. Surprisingly, PHA-induced blastogenesis was inhibited by the same dose of Achatinin_H as caused mitogenic activity in resting lymphocyte culture. The degree of suppression was higher for the lymphocytes isolated from pregnant rat blood compared to the non-pregnant control. Since the ⁵¹Cr-uptake assay and the cell viability test results negate the potential cytotoxic activity of this protein, the immunosuppression induced in the presence of PHA by Achatinin_H may be the additive effect of two mitogens causing an increased cell-density-dependent arrest. Achatinin_H does not have complement-like activity, but induces potent polyclonal activation of B cells as measured by the reverse hemolytic plaque assay.