Macrophages expressing arginase 1 and nitric oxide synthase 2 accumulate in the small intestine during Giardia lamblia infection

Nitric oxide (NO) has been shown to inhibit Giardia lamblia in vitro and in vivo. This study sought to determine if Giardia infection induces arginase 1 (ARG1) expression in host macrophages to reduce NO production. Stimulations of RAW 264.7 macrophage-like cells with Giardia extract induced arginase activity. Real-time PCR and immunohistochemistry showed increased ARG1 and nitric oxide synthase 2 (NOS2) expression in mouse intestine following infection. Flow cytometry demonstrated increased numbers of macrophages positive for both ARG1 and NOS2 in lamina propria following infection, but there was no evidence of increased expression of ARG1 in these cells.