Pathological effects in lymphoid tissues of the spleen, lymph nodes, and Peyer's patches in cyclosporin-treated cynomolgus monkeys.

Germinal center/lymphoid follicle area ratio and CD3/CD20-positive area ratio were calculated for the spleen, submandibular and mesenteric lymph nodes, and Peyer's patches in cynomolgus monkeys treated orally with cyclosporin A (CsA), an immunosuppressant which blocks Ca2+/NFAT signaling. A difference in hypocellularity between lymphoid organs was observed after CsA administration in a dose-dependent manner. Regarding drug efficacy, the highest susceptibility to CsA tended to be shown in the Peyer's patches, and susceptibility then descended in the order of the spleen, mesenteric lymph nodes, and submandibular lymph nodes. It was shown in the present study that decreases in germinal center area and CD3-positive area were sensitive indicators of the efficacy of CsA for lymphoid organs and tissue in cynomolgus monkeys.