Protective immunity against challenge infection with Trichinella spiralis in the rat

Protective immunity and immune response were studied in rats after primarily infection with Trichinella spiralis. The parameters measured include serum antibody isotype responses, mesenteric lymph node (MLN) cell and spleen cell proliferation responses in vitro, and the levels of interferon (IFN)-γ, interleukin (IL)-2, IL-4 and IL-10 as markers of the T-helper (Th) subset. Protective immunity was assessed by the degree of expulsion of adult worms from the rat intestine. Protective immunity against adult worms after challenge infection was 99.80%. Although IFN-γ, IL-2, IL-4 and IL-10 in both the MLNs and spleen were detected, IFN-γ and IL-2 levels were higher in the spleen than in the MLNs, and IL-4 and an increased amount of IL-10 was released in the MLNs as compared to the spleen. The levels of the specific immunoglobulins (Ig) G, IgM, IgG1 and IgG2a on week 6 after primary infection, and on day 7 after challenge infection, were higher as compared to levels in uninfected rats that only received a challenge infection (P < 0.001), whereas the antibody level of IgG1 was significantly elevated from that of IgG2a (P < 0.001). These results demonstrate that Th1 type responses predominated. In addition, as Th2 type cytokines were also produced, it is proposed that the protective immunity by primary infection was also related to the Th1 type responses.