Journal of Fish Diseases 1989, 12, 459-465 Immunoglobulin heterogeneity in the rainbow trout, Salmo gairdneri Richardson C. SANCHEZ, J. DOMINGUEZ & J. COLL Department of Virology, Jnstituto Nacional de Investigaeiones Agrarias. Madrid, Spain Abstract. Hetereogeneity of rainbow trout immunoglobulins was demonstrated by using monoclonal antibody 1A6 and polyacrylamide-gradient gel eleetrophoresis. Immunoglobulins defined by ELISA using monoclonal antibody 1A6 were about 30% of the total immunoglo- bulins, detected by EUSA using polyclonal antibodies, in healthy rainbow trout. In trout obtained from farms with a previous history of infectious viral diseases, lA6-immunoglobulins were only about 14% of the total. Several serum pools from infected trout could be totally depleted of 1 A6-immunoglobulins (about 12% of total immunoglobulins) by affinity chromato- graphy over Sepharose immobilized monoelonal antibody 1A6. Polyacrylamide-gradient gel electrophoresis under denaturing conditions of total immunoglobulins, 1A6 immunoglobulins and no-lA6 immunoglobulins purified by affinity chromatography, showed a majority heavy chain of 70 KDa and a minority heavy chain of about 60 KDa, two light chains of 24 and 26 KDa, and a 11-14 KDa polypeptide. Introduction Immunoglobuhns (Ig) molecules in salmonids are tetramers consisting of a basic structure of eight light chains and eight heavy chains (Voss, Groberg & Fryer 1980; Ingram & Alexander 1979; Kobayashi, Hara, Takano & Hirai 1982). The molecular weight of the whole molecule is about 700 KDa. Selected monoclonal antibodies to catfish Ig distinguished two different light chains (Lobb, Olson & Clem 1984; Lobb 1986) and at least four antigenically different heavy chains (Lobb & Olson 1988). However, the scarce data using monoclonal antibodies to trout Ig (DeLuca, Wilson & Warr 1983) and the low resolution of separation techniques used has not yet cast any light on this subject in the trout (Warr, De Luca & Anderson 1983). The existence of a J-like chain has not yet been reported for salmonids (Kobayashi et al. 1982) and it has not been detected by conventional polyacrylamide gel electrophoresis under denaturing conditions (Warr et al. 1983). This work describes the Ig variants measured using monoclonal antibody 1A6 against trout Igs. This variant appeared in all individual trout tested and its relative abundance decreases in virus-infected trout. The present authors also report the presence of two heavy and two light chains of different molecular weights and a J-like chain all separated by polyacrylamide gradient gel electrophoresis. Materials and methods Fish Disease-free rainbow trout, Salmo gairdneri Richardson, of about 20 cm in length were obtained from the hatchery at Escuela Tecnica Superior de Ingenieros de Montes, Polithecnic University Correspondenee: Carmen Sanehez, Instituto Nacional de Investigaeiones Agrarias CRIDA 06, Department of Virology, Embajadores, 68. 28012 — Madrid. Spain. 459