Localization of VIP receptors and SP receptors in the human spleen. (A) CD3 immunohistochemical staining of the periarterial lymphatic sheaths (arrows). Bar = 1 mm. (B) Autoradiogram showing total binding of ¹²⁵I-VIP. Preferential labeling is seen in the periarterial lymphatic sheets (arrows). Nonspecific binding is negligible. (C) Hematoxylin-eosin staining showing several central arteries (arrowheads) Bar = 1 mm. (D) Autoradiogram showing total binding of ¹²⁵I-BH-SP. Only the central arteries are labeled. Nonspecific binding is negligible.