CD41 is a reliable identification and activation marker for murine basophils in the steady state and during helminth and malarial infections.

Basophils, a rare leukocyte population in peripheral circulation, are conventionally identified as CD45(int) CD49b(+) FcεRI(+) cells. Here, we show that basophils from blood and several organs of naïve wild-type mice express CD41, the α subunit of α(IIb)β₃ integrin. CD41 expression on basophils is upregulated after in vivo IL-3 treatment and during infection with Nippostrongylus brasiliensis (Nb). Moreover, CD41 can be used as a reliable marker for basophils, circumventing technical difficulties associated with FcεRI for basophil identification in a Nb infection model. In vitro anti-IgE cross-linking and IL-3 basophil stimulation showed that CD41 upregulation positively correlates with augmented surface expression of CD200R and increased production of IL-4/IL-13, indicating that CD41 is a basophil activation marker. Furthermore, we found that infection with Plasmodium yoelii 17X (Py17x) induced a profound basophilia and using Mcpt8(DTR) reporter mice as a basophil-specific depletion model, we verified that CD41 can be used as a marker to track basophils in the steady state and during infection. During malarial infection, CD41 expression on basophils is negatively regulated by IFN-γ and positively correlates with increased basophil IL-4 production. In conclusion, we provide evidence that CD41 can be used as both an identification and activation marker for basophils during homeostasis and immune challenge.