Dynamic changes of macrophage activation in mice infected with Trichinella spiralis

Trichinellosis is a serious food-borne parasitic zoonosis worldwide. Different host macrophage subsets play various roles during helminth infection; however, the dynamic changes in macrophage subsets following Trichinella spiralis infection have not been reported. Here, flow cytometry and immunofluorescence were used to assess macrophage activation in mesenteric lymph nodes (MLN), spleen, intestine, and muscle from T. spiralis-infected mice at 1, 5, 15, and 30 days post infection (dpi). Macrophages in the intestine, MLN, and spleen tended to be activated M1-type at 1 and 5 dpi, while at 15 dpi, M2-type macrophages started to become a major constituent of the spleen macrophage population, and in the intestine and MLN, macrophages were primarily mixed M1 and M2 type. At 30 dpi, macrophages in the intestine, muscle, MLN, and spleen were all mainly activated M2 cells. Additionally, mouse macrophages were cleared and the adult T. spiralis load were determined to evaluate the impact of macrophages on adult parasite expulsion. The results suggested that predominantly M1 macrophages contribute to adult T. spiralis expulsion in the enteral stage of infection. At the newborn larvae migration stage, M2 macrophage-mediated immunity had a weak scavenging effect on adults, but primarily promoted tissue repair and assisted muscle larva immune escape. Our study reveals further details of the interaction between T. spiralis and the host immune system.