AN IN-VITRO STUDY ON THE MECHANISM OF INNATE IMMUNITY IN CRYPTOBIA-RESISTANT BROOK CHARR (SALVELINUS-FONTINALIS) AGAINST CRYPTOBIA-SALMOSITICA

Fresh plasma from Cryptobia-resistant brook charr (Salvelinus fontinal is) lysed Cryptobia salmositica under in vitro conditions. However, th e parasite was not lysed if the plasma was heat-inactivated at 37 degr ees C for 2 h or after the addition of ethylenediaminetetraacetic acid (EDTA) to chelate the free Mg2+ ions. Addition of Mg2+ ions to EDTA-c helated plasma restored parasite lysis. Treatment of Cryptobia-resista nt plasma with either ethylenebis(oxyethylenenitrilo)tetraacetic acid, a Ca2+-chelating agent, or cobra venom factor did not reduce their ly tic titres. The alternative pathway of complement activation is the me chanism of innate immunity against C. salmositica. The present study a lso shows that there is functional heterogeneity amongst the complemen t components activated via the alternative pathway within a species (b rook charr) and between species (brook charr and goldfish) of fishes.