Route of immunization influences the generation of antibody secreting cells in the gut of rainbow trout ( Oncorhynchus mykiss)

Although fish lack the Peyer's patches of mammals, histological and functional studies have demonstrated that the intestine of several species of teleost is rich in leucocytes. Georgopoulou and Vernier isolated leucocytes from the intestine of rainbow trout and identified antibody secreting cells (ASC) and antigen binding cells. Previously, intestinal ASC have been demonstrated using the haemolytic plaque assay, but several important features of intestinal antibody secretion, such as the contribution of the intestine to the antibody secretion of the whole animal, the long-term kinetics and the response after antigenic stimulation by different routes, remain obscure. Recently, an improved technique for the enumeration of ASC, called the ELISPOT assay has become available. It has already been applied to fish successfully and it was employed here to determine the temporal and quantitative appearance of ASC in the head kidney (HK) and intestine of rainbow trout following immunization with Aeromonas salmonicida via the peroral or intraperitoneal (IP) routes.