Different subpopulations of haemocytes in juvenile, adult and Trichobilharzia ocellata infected Lymnaea stagnalis: a characterization using monoclonal antibodies.

In the pond snail Lymnaea stagnalis, intermediate host of the schistosome Trichobilharzia ocellata, macrophage-like blood cells (haemocytes or amoebocytes) play an important role in internal defence (Sminia 1972; Van der Knaap et al. 1981). The population of haemocytes is heterogeneous: cells vary in morphology, lysosoma] enzyme contents and phagocytic activity. Despite the heterogeneity in form and function, only one type of haemocyte is thought to be present in the haemolymph of (adult) L. stagnalis (Sminia et al. 1983). The observed differences could be expressions of the stage of maturation or activation of what is basically one type of haemocyte. The haemogram is age-dependent:juvenile snails have an immature haemogram dominated by small, poorly differentiated haemocytes with low immunocompetence, whereas in the circulation of adult snails large, differentiated, highly immunocompetent cells prevail (Dikkeboom et al. 1984, 1985). Also, in the course of infection with T. ocetlata the morphology and phagocytic capacity of the haemocytes change (Van der Knaap et al. 1984). To characterize differences between or changes in cell (sub)populations (caused by e.g. ageing or infection), it is useful to have specific and sensitive markers for the cells. Such markers exist in the form of monoclonal antibodies which can reveal even the slightest antigenic differences among cells. Applications of monoclonal antibodies to the study of gastropod blood cells have recently been published by Yoshino and Granath (1983, 1985). In this paper we give the preliminary results of a study aimed at characterizing (antigenically) distinct subpopulations of haemocytes in L. stagnalis and at assessing differences in the haemograms of juvenile, adult and T. ocellata-infected snails, using several monoclonal antibodies,