Immunization with Trichinella spiralis Korean isolate larval excretory-secretory antigen induces protection and lymphocyte subset changes in rats

Protection and immune responses were studied in rats immunized with Trichinella spiralis muscle stage larval excretory-secretory antigen (ES Ag) without adjuvant. Protection was assessed by the degree of adult worm burden and the yield of muscle (diaphragmatic) larvae after challenge infection with live larvae. Lymphocyte subsets were identified by flow cytometry in the spleen and peripheral blood. Cytokine production and specific IgG, IgG1 and IgG2a antibody responses were measured. Immunization with ES Ag produced highly significant protection against adult stages (98.4%) and muscle larvae (82.9%). Th2 type cytokines (IL-10, IL-4) were predominant. Anti-muscle stage larval ES Ag antibody was significantly elevated in the order IgG2a > IgG1 > IgG on the 2nd day after final immunization and on the 7th day after challenge infection. Expression of CD4+ and the CD4+/CD8+ ratio from spleen and blood were significantly increased compared to the control. These results demonstrate that immunization with T. spiralis antigen can elicit robust immune response, resulting in complete protection against infective larvae, and this protection can be achieved without the use of any adjuvant.