We transferred sera (150 μl/mouse, one time) isolated from anti-LAG-3 or isotype Ab-treated PD-L1-/- mice 18, 32, or 72 days post Py-infection, into WT B6 recipient mice that were subsequently infected with Py. Data reveal a delayed onset and peak blood parasitemia, and lower weight loss in mice treated with day 72 sera, but no beneficial trends were observed in day 18 or 32 sera transfers. This evidence concerns the gene LAG3 and parasitic infectious disease.