CD69 and viral infectious disease: As seen in Fig. 2A, CD69 is poorly expressed on blood and BAL neutrophils from uninfected mice, but strongly upregulated during viral infection, perhaps reflecting the responsiveness of CD69 to upregulation in the presence of pro-inflammatory cytokines such as IFN-α and IFN-γ [21] which would be produced at high levels in the lungs of infected, but not naïve, mice.