Surface morphology and characteristics of hemocytes of Biomphalaria glabrata (Pulmonata: Planorbidae) from two geographic sources.

Biomphalaria glabrata is a fresh water snail of medical importance since it is the intermediate host of the trematode Schistosoma mansoni. The internal defense system of mollusks is mostly represented by circulating elements of the hemolymph (hemocytes). The infectivity of S. mansoni to B. glabrata is determined by genetic factors and evolutionary adaptations. In the present work factors about the parasite/snail relationship were evaluated, especially those related to the morphology and characteristics of the surface of cells present in the hemolymph of two strains of B. glabrata: a strain with high susceptibility to S. mansoni (Puerto Rico, PR) and a strain with medium susceptibility (Caripe, Ca). Hemolymph was collected by cephalopodal puncture; a total and a differential count of hemocytes were done in dyed preparations and through scanning electron microscopy (SEM). Results from both strains show a high quantitative variability of the total hemocyte count. Hemocytes dyed with May-Grünwald Giemsa showed cells with a basophilic nucleus predominantly in PR (61.7%), dense and strongly basophilic in Ca (71.2%) with significant differences between them. Through SEM round cells with a corrugated surface were observed (6-10microm), hemocytes with an irregular spongy surface (12microm), others with many projections (16microm) and cells not reported in similar to erythrocytes (21microm). Hemocytic cells from both strains confirmed cytoadherence and encapsulation were confirmed in the hemocytic cells from both strains, while no differences associated to the susceptibility of the strains were observed after 2 h of parasite-hemocyte incubation.