Localization of TGF-α in promonocytes. Ultrathin cryosection of a promonocyte of the bone marrow labeled to detect TGF-α. Many granules are present strongly labeled for TGF-α (large arrows). Mitochondria (m) and nucleus (n) are negative. Small arrows are pointing to a large bundle of filaments characteristic for promonocytes. Bar = 300 nm.