LAG3 constrains anti-parasitic response by effector CD4(+) T-cell in early Echinococcus multilocularis-infected mice.

BACKGROUND: Immune checkpoint molecules such as lymphocyte activation gene-3 (LAG3) play a critical role in modulating host-pathogen interactions during chronic parasitic infections; however, their functions in early infection remain poorly defined. Using a murine model infected with Echinococcus multilocularis (E. multilocularis), a lethal helminth causing alveolar echinococcosis (AE), we elucidate the stage-specific regulatory functions of LAG3 in CD4(+) T cell immunity during early infection. METHODS: Echinococcus multilocularis-infected mice were employed as the experimental model. Flow cytometry was used to analyze LAG3 expression on CD4(+) T cell subsets and the production of intracellular cytokines. The in vivo functional role of CD4(+) T cells was further investigated using LAG3-knockout mice and adoptive T cell transfer models. Infected wild-type mice received LAG3 blocking antibody treatment, with parasite burden assessed by measuring metacestode weight. Hepatic pathology was evaluated using hematoxylin and eosin and Masson's trichrome staining. RESULTS: We found that LAG3 was predominantly expressed on hepatic effector CD4(+) T (CD4(+) Teff) cells, particularly the CD69(+) subset in the early stages of E. multilocularis infection. Functional analysis showed that LAG3-expressing CD4(+)CD44(+) T cells secreted elevated levels of interleukin-4 (IL-4) and IL-10 at 2 and 4 weeks post-infection. LAG3 deficiency further enhanced the production of interferon-y (IFN-γ), IL-4, and IL-10 by splenic CD4(+) T cells in the initial infection phase, which may contribute to the slight suppression of E. multilocularis growth and development observed in the livers of LAG3-knockout mice. In an adoptive transfer model of early E. multilocularis infection, LAG3(-/-)CD4(+) T cells exhibited a greater propensity to differentiate into CD4(+) effector T (Teff) cells and produced higher levels of IFN-γ and IL-10 in both the livers and spleens of recipient mice. Finally, early administration of anti-LAG3 monoclonal antibody (mAb) reduced metacestode burden-though the change was not statistically significant-and concurrently exacerbated hepatic inflammation and fibrosis. CONCLUSIONS: Our study reveals a previously unrecognized role for LAG3 as an immune checkpoint during early E. multilocularis infection, highlighting its function in limiting anti-parasitic CD4(+) T cell responses. Thus, while timed LAG3 blockade may represent a potential therapeutic strategy for AE, our data underscore the critical importance of stage-specific intervention to balance parasitic clearance with the control of fibrosis and tissue damage.