Abstract
S. japonicum infection can induce granulomatous inflammation in the liver of the host. Granulomatous inflammation limits the spread of infection and plays a role in host protection. Toll-like receptor 7 (TLR7) is an endosomal TLR that recognizes single-stranded RNA (ssRNA). In this study, the role of TLR7 in S. japonicum infection-induced hepatitis was investigated in both normal and TLR7 knockout (KO) C57BL/6 mice. The results indicated that TLR7 KO could aggravate S. japonicum infection-induced damage in the body, with less granuloma formation in the tissue, lower WBCs in blood, and decreased ALT and AST in the serum. Then, the expression of TLR7 was detected in isolated hepatic lymphocytes. The results indicated that the percentage of TLR7+ cells was increased in the infected mice. Hepatic macrophages, DCs, and B cells could express TLR7, and most of the TLR7-expressing cells in the liver of infected mice were macrophages. The percentage of TLR7-expressing macrophages was also increased after infection. Moreover, macrophages, T cells, and B cells showed significant changes in the counts, activation-associated molecule expression, and cytokine secretion between S. japonicum-infected WT and TLR7 KO mice. Altogether, this study indicated that TLR7 could delay the progression of S. japonicum infection-induced hepatitis mainly through macrophages. DCs, B cells, and T cells were involved in the TLR7-mediated immune response.
Highlights
Schistosomiasis is the most important helminth disease in the world from a public health perspective (Llanwarne and Helmby, 2021)
To explore the role of Toll-like receptor 7 (TLR7) in mice infected with S. japonicum, the survival rates of wild-type (WT) and TLR7 knockout (KO) mice infected with S. japonicum were recorded
The survival results showed that the majority of infected mice did not die before 6 weeks post infection, while approximately half of TLR7 KO mice died within 6 weeks post infection, indicating that TLR7 may protect the host from death in the early phase of S. japonicum infection
Summary
Schistosomiasis is the most important helminth disease in the world from a public health perspective (Llanwarne and Helmby, 2021). It is estimated that approximately 230 million people in the world are still under the threat of schistosomiasis (Lackey and Horrall, 2020). During infection with S. japonicum, cercariae, juvenile worms, adult worms and eggs can cause damage to the host (Llanwarne and Helmby, 2021). Granulomatous inflammation can lead to pathological changes, but granulomatous inflammation limits the spread of infection and plays a role in host protection (Hams et al, 2013). Extensive granulomatous fibrosis causes portal hypertension, which results in irreversible cirrhosis and advanced schistosomiasis, leading to host death (Lackey and Horrall, 2020)
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