Lectins and saccharides inLymnaea stagnalis haemocyte recognition

Lectins as important non-self-recognition factors are present on molluscan haemocytes as membrane receptors or in cell-free plasma as soluble recognition factors. The recognition mediated by them can be operational in Ca²⁺-dependent and-independent ways. In our phagocytosis system,Lymnaea stagnalis haemocytes and rabbit erythrocytes served as effector and target cells, respectively. The Ca²⁺-dependent phagocytosis was inhibited by aminosaccharides and their acetylated forms,l-fucose, laminarin (a β-1,3-glucan) and mannan. By omitting calcium from the buffer, the phagocytosis was reduced nearly to zero. However, certain heterologous (commercial) lectins stimulated the process to levels detected in Ca²⁺-containing buffer. Knowing lectin targets on haemocytes and erythrocytes, lectin specificities and glycosylation, we could infer the role of heterologous lectins in recognition: some lectins created bridges between carbohydrates on effector and target cells whereas the others functioned as opsonins, i.e. they bound to saccharides on target cells and created in this way attractive epitopes for haemocyte receptors; both lectin types enabled subsequent phagocytosis. Thus, Ca²⁺-dependent and-independent lectin-mediated recognition has been demonstrated. Infection byTrichobilharia szidati did not substantially impair the recognition process. The role of soluble lectins ofL. stagnalis origin (homologous lectins) remains to be solved.