FCGR2B and viral infectious disease: Following viral infection, a significant increase in the frequency of microglia expressing iNOS was found in FcgR2b KO mice (8.07%) when compared with either WT (3.68%) (***p < 0.001) or Fcer1g KO mice (3.08%) (***p < 0.001) at 14 dpi (Fig. 5A).