HUMORAL IMMUNE-RESPONSE OF TURBOT, SCOPHTHALMUS-MAXIMUS (L), TO ANTIGENS FROM TETRAMICRA BREVIFILUM MATTHEWS AND MATTHEWS, 1980 (MICROSPORA)

The humoral immune response of turbot. Scophthalmus maximus (L.), to a ntigens from the microsporean parasite Tetramicra brevifilum Matthews and Matthews, 1980, was studied. Thirty days after intraperitoneal imm unization with whole T. brevifilum spores in Freund's complete adjuvan t, double indirect ELISA indicated that initial production of antibodi es to parasite surface antigens was considerably higher than productio n of antibodies to the antigens contained in a crude extract (CE) of s pores. Following re-immunization without adjuvant on day 30, levels of antibodies to surface antigens gradually declined. whilst levels of a ntibodies to CE antigens increased. The antibody response of intraperi toneally immunized fish was characterized by Western blotting of total soluble antigens obtained by heating and reduction of T. brevifilum s pores at 95-100 degrees C in Tris-HCl buffer containing SDS and dithio threitol: a series of bands with molecular weights between 20 and 53 k Da was recognized by immunized turbot sera. Four additional bands (wit h molecular weights between 15 and 18 kdA) were recognized by serum fr om re-immunized fish. ELISA studies of sera from naturally infected fi sh revealed a surprisingly low incidence of strong T. brevifilum serop ositivity (61% individuals); antibodies to surface antigens predominat ed in seropositive individuals. The low background response levels and high sensitivity of the ELISA used in this study indicate that the as say is of value for the monitoring of serum antibody levels in turbot. However, given the relatively low seropositivities observed in natura lly infected turbot, particularly to CE antigens, the use of anti-T. b revifilum serum antibody levels for the diagnosis of infection by this parasite may lead to false negative results.