4-1BB (CD137), another TNFRSF member predominantly expressed on T cells, has been shown to have non-redundant roles with OX40 in enhancing CD4 T cell function.19,20 Given that CD4 T cells play a key role in anti-Plasmodium immunity by providing help to B cells, we investigated the role of exogenous 4-1BB stimulation in a rodent malaria model. Here, TNFRSF9 is linked to malaria.