IMMUNE-COMPLEX TRAPPING IN THE SPLENIC ELLIPSOIDS OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Rainbow trout (Oncorhynchus mykiss), immunised with horseradish peroxi dase, were given horseradish peroxidase intravenously, and the trappin g of antigen in the spleen was followed 1, 24, and 48 h after injectio n. After 1 h, the localisation of horseradish peroxidase indicated tha t the antigen had been extensively trapped in the walls of the splenic ellipsoids. The colocalisation of horseradish peroxidase with rainbow trout immunoglobulin M and complement factor 3 was shown with a doubl e immunofluorescence technique and suggested that horseradish peroxida se was trapped in the form of immune complexes. After 24 and 48 h, ver y little horseradish peroxidase was detected in the ellipsoids, and ho rseradish peroxidase was mainly found in association with large cells with prominent cytoplasmic extensions. In nonimmunised fish given hors eradish peroxidase intravenously, antigen was not detected in ellipsoi ds. Thus, the observed difference between immunised and nonimmunised t rout suggests a specific role for the splenic ellipsoids in rapid immu ne-complex trapping and invites speculation on its significance in a s econdary immune response.