EPAS1 and infection: HIF-1 is a heterodimer containing an oxygen-regulated HIF-1α and HIF-2α subunits and a constitutively expressed HIF-1β subunit.218 HIF-1α induced by M1 polarized cells via NF-кB dependent manner mediates transcription of iNOS.219 Mice with conditional deletion of macrophage HIF-1α exhibit a reduction of antimicrobial activity and failure to constrain the systemic spread of infection.219 In contrast to HIF-1α, expression of HIF-2α was induced in M2-polarized macrophages.