CRYPTOCOTYLE-LINGUA IN MULLET, CHELON-LABROSUS - SIGNIFICANCE OF METACERCARIAL EXCRETORY PROTEINS IN THE STIMULATION OF THE IMMUNE-RESPONSE

'O' group mullet, Chelon labrosus, were experimentally infected with C ryptocotyle lingua (Heterophyidae) by tail dip in a suspension of cerc ariae. Metacercariae were excised after 1 and 24 hours and prepared fo r TEM and post-embedding immunogold labelling. Antisera to cercariae o f C. lingua were raised in adult mullet by natural infection via the s kin and by intra-peritoneal injection of sonicate. The membrane-bound vesicles within the syncytial lining of the metacercarial excretory ve sicle were found to be intensely antigenic with both antisera; the epi dermal secretory bodies type 5 within the cystogenous glands gave a po sitive response. Penetration gland contents were not found to be antig enic with either antiserum. Discharge of the membrane-bound vesicles c oinciding with both the reorganization of the lining of the metacercar ial excretory vesicle and with cyst wall formation appears to be of si gnificance in the initiation of the host immune response. That the ter m 'excretory vesicle' in Digenea may be a misnomer is discussed in the light of current information regarding the wide range of functions at tributed to this structure.