CHARACTERIZATION OF A MONOCLONAL-ANTIBODY AGAINST THE 47-KDA ANTIGEN OF CRYPTOBIA-SALMOSTICA KATZ AND ITS USE IN AN ANTIGEN CAPTURE ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR DETECTION OF PARASITE ANTIGEN IN INFECTED RAINBOW-TROUT, ONCORHYNCHUS-MYKISS (WALBAUM)

A monoclonal antibody (designated MAb-007) was produced against the pa thogenic haemoflagellate Cryptobia salmositica Katz. This IgG3 antibod y recognized the 47-kDa antigenic polypeptide of C. salmositica (SDS-P AGE and Western immunoblotting). The antibody did not agglutinate live parasites, and there was no change in the staining intensity of the 4 7-kDa band on Western immunoblots after immunoabsorption of MAb-007 wi th live intact parasites. The 47-kDa antigen recognized by MAb-007 was localized in the cytoplasm of the parasite (immunogold labelling and electron microscopy). The monoclonal antibody crossreacted with the 47 -kDa polypeptides of C. bullocki Strout and C. catostomi Bower & Woo. It was used in an antigen-capture ELISA for the detection of parasite antigen in the plasma of rainbow trout inoculated with the parasite, o r with an attenuated vaccine strain of C. salmositica. All pre-infecti on plasma were negative while all infected fish with detectable parasi taemias were positive for antigen at 1-9 weeks after infection. Parasi te antigen was even detected in vaccinated fish that were negative for parasites using the wet mount microscopic technique. The antigen-capt ure ELISA detected C. salmositica antigen in whole cell lysate prepara tions at concentrations as low as 0 . 5 mu g ml(-1). Fifty microlitres of fish plasma was required in the antigen-capture ELISA, and the use of a plate reader and 96-well plates facilitated rapid analysis of a large number of plasma samples. The sensitivity of the assay makes it a potentially useful tool for detection of Cryptobia infections.