Comparison of concanavalin A reactive determinants on isolated haemocytes of parasite- infected and non-infected freshwater crayfish

The specific binding of concanavalin A (Con A) to semigranular (SG) and granular (G) cells of the crayfishes Pacifastacus lelliusculus and Astacus astacus was shown by in vitro agglutination of fixed haemocytes and by direct labelling with fluorescein isothiocyanate-conjugated Con A (FITCCon A). When non-fixed cell monolayers from both species of crayf~sh were treated with FITC-Con A, capping of G cells was observed and nearly all of the SG cells showed patching. The percentage of capforming G cells from Psorospermium haeckelii-infected A. astacus w a s clearly higher than that of noninfected crayfish. Also in the signal crayfish P. leniusculus w h ~ c h carries the crayfish plague parasite Aphanomyces astaci within the cuticle, a high percentage of cap-forming G cells was present. In A. astacus which received a Zymosan injection, a higher percentage of cap formation of G cells was observed compared with that of control crayfish. These results show that the presence of parasites alters the binding pattern of Con A to the haemocyte surface dnd this altered binding pattern suggests that these cells have become activated for cellular defence reactions within the host haemolymph.