Localization of VIP receptors, SS receptors, and SP receptors in successive sections of a human Peyer's patch. (A) CD3 immunohistochemical staining. Bar = 1 mm. (B) Autoradiogram showing total binding of ¹²⁵I-VIP. Arrows point towards VIP receptors located in the peripheral zone of the lymphoid follicle. (C) Autoradiogram showing total binding of¹²⁵I-Tyr³-octreotide. Arrowhead shows SS receptors in the germinal center. (D) Autoradiogram showing total binding of ¹²⁵I-BH-SP. SP receptors are located in the blood vessels.