Trichobilharzia ocellata: Quantification of effects on haemocytes of the pond snail Lymnaea stagnalis by morphometric means.

To identify functionally different subpopulations, we quantified by morphometric means the spreading activity of circulating haemocytes of the pond snail Lymnaea stagnalis, recognized by monoclonal antibodies (5 surface and 5 cytoplasmic). The influence of snail age and of the different intramolluscan stages of the compatible avian schistosome Trichobilharzia ocellata on this activity were studied. The antibody-recognized cells could be separated into two groups, differing in their spreading activities. The probes detecting cytoplasmic markers recognized the majority of cells (78-95%). These were active (well spreading), differentiated cells. The surface probes recognized a smaller part (12-38%) of the total haemocyte population. These harmocytes were less active (less spreading), and were predominantly immature cells. The relative sizes of the antibody-detected subpopulations were not affected by snail age or infection with T. ocellata. The maximal size (planimetric area) attained after attaching to glass of all cells increased between day 0 (juvenile snails) and about 6 weeks post (sham) exposure and then decreased. Infection had little effect on the spreading activity of the more differentiated cells. The less differentiated cells showed a larger spreading activity when the parasite was present as mother sporocyst and also when the digestive gland area became colonized by growing daughter sporocysts.