CD40LG and giardiasis: In comparison to germ-free mice, Giardia-infected conventional mice showed higher levels of IgA in the intestinal fluid and higher levels of IgG and IgM in the serum, further corroborating that the microbiota plays important roles in the adaptive immune response during Giardia infection and is a driving factor in some aspects of Giardia pathogenesis (Torres et al., 2000).