Th2-related cytokines are associated with Fasciola gigantica infection and evasion in the natural host, swamp buffalo

Abstract

The infection of ruminants by Fasciola spp. always induces a non-protective Th2-type immune response. However, little is known about changes in the local and systemic immune environment during F. gigantica migration in buffalo. In this study, native swamp buffaloes were each infected with 500 viable F. gigantica metacercariae. Mesenteric lymph node (MLN), hepatic lymph node (HLN), spleen, and serum samples were collected from control and infected buffaloes at 3, 10, 28, 42, 70, and 98 days post-infection (DPI). The mRNA expression levels of the Th1- and Th2-related cytokines IL-2, IL-4, IL-5, IL-6, IL-10, IL-12p40, IFN-γ, TNF-α, and CD4 were measured during different infection stages in the MLNs, spleens, and HLNs using quantitative real-time PCR (qRT-PCR). Levels of the specific anti-ESP isotype antibodies IgG, IgG1, and IgG2 were used to reflect changes in humoral immunity. The results of this study indicated that swamp buffaloes were susceptible to F. gigantica infection, and that susceptibility to this infection was closely related to the cytokine environment associated with the Th2-type immune response. The MLNs showed a mixed Th1- and Th2-type immune response during the acute infection stages, after which the production of these cytokines returned to normal. Cytokine expression in the HLNs also expressed a mixed Th1- and Th2-type immune response during the early infection stages. When the infection became chronic, the typical Th2 immune response was induced in the HLNs. At the acute infection stages, the spleen exhibited a Th2 immune response. Nevertheless, cytokines associated with the Th1 and Th2 immune responses were upregulated at 98 DPI. In addition, the total IgG and IgG1 of the parasite-specific antibodies increased. This suggested that the Th2-related cytokines and IgG1 induced by F. gigantica infection might mediate successful F. gigantica infection in the natural host, swamp buffalo.