Lectin-induced modulation of snail hemocyte surface determinants: clearance of Con A-receptor complexes

The fate of surface concanavalin A (Con A)-receptor complexes on hemocytes from two stocks of the snail, Biomphalaria glabrata (PR albino and 10-R2), was studied using both direct (Con A-FITC) and indirect (biotin-Con A, avidin-FITC) fluorescent staining methods. The results of experiments in which living hemocytes were exposed first to biotin-Con A, followed by fixation and subsequent treatment with avidin-FITC to localized surface-bound lectin, demonstrate that Con A complexes are rapidly cleared from hemocyte plasma membranes. Experiments employing Con A-FITC further indicate that clearance is accomplished through an internalization process whereby Con A-complexes are endocytosed and eventually accumulate as a single intracellular aggregate of fluorescent material in the cell body of each hemocyte. In addition, a redistribution of surface complexes into patches and caps is concomitant with receptor clearance, with a maximum frequency of patching (approx. 45%) and capping (approx. 30%) occurring within 5 and 10 min., respectively, of initial Con A exposure. PR albino and 10-R2 snail hemocytes appear indistinguishable with regards to their responsiveness to Con A-binding. The close similarity in the behavior of Con A complexes or circulating hemocytes from both snail stocks further support the conclusion that Con A-reactive determinants and their associated membrane components probably represent identical molecular populations on PR albino and 10-R2 B. glabrata blood cells.