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

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.

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.

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.

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.