For double immunohistochemistry of the human placentas, 8-µm thick placental sections were fixed in 4% paraformaldehyde, permeabilized with 0.2% Triton X-100, and blocked in 3% BSA overnight. Primary antibodies used were: rabbit anti-citH3 (1:200, Abcam), rabbit anti-MPO (1:200, Abcam), mouse anti-NE (1:200, HM2174, Hycult Biotech), and rabbit anti-IRS1 (1:200, sc-559, Santa Cruz). Sections were incubated in a light-protected humidified chamber with Alexa 488-conjugated goat anti-rabbit (1:1,000, Life Technologies) and Alexa 647-conjugated goat anti-mouse (1:1,000, A21237, Life Technologies) secondary antibodies. Sections were stained with DAPI (1:10,000) and mounted in Mowiol (Sigma-Aldrich). In addition, a further consecutive section was stained using H&E for comparison against immunostained tissues. The slides were observed under an Olympus BX61 Diana fluorescent microscope and photographed.