Giardia duodenalis is one of the most widespread intestinal parasitic infections in humans. Infections can by asymptomatic or cause diarrhea, cramps and nausea. The Singer lab has used a mouse model of Giardia infection to understand the development of immune responses against the parasite and to determine which responses contribute to parasite elimination and which contribute to pathology. Recent studies in the lab have focused on the CD8+ T cell response and the role of macrophages in this system. Activation of CD8+ T cells is dependent on the microbiota and contributes to reduced nutrient absorption following infection. Macrophage responses are also somewhat dependent on microbiota and preliminary results suggest an anti-inflammatory phenotype.