PITUITARY ADENYLATE CYCLASE-ACTIVATING PEPTIDE (PACAP) IMMUNOLOCALIZATION IN LYMPHOID-TISSUES OF THE RAT

Pituitary adenylate cyclase activating peptide (PACAP) is a novel pept ide isolated from the ovine hypothalamus. PACAP exists in 2 molecular forms with 27 (PACAP27) or 38 (PACAP38) amino acid residues. PACAP loc alization was studied by immunohistochemical methods in central (bone marrow and thymus) and peripheral (spleen, lymph nodes and duodenal mu cosa) lymphoid tissues with antisera raised against PACAP27 or PACAP38 . PACAP-positive cells were found in all lymphoid tissues examined. Th ese cells were highly positive for PACAP38 but were negative for PACAP 27. Morphologically, they were small mononuclear cells with relatively scarce cytoplasm and lymphocyte-like features. PACAP38-positive cells were abundant in peripheral lymphoid tissues (i.e., mesenteric lymyh nodes). In the duodenal mucosa, PACAP38-positive cells were located ei ther in the lamina propria or epithelium. These results suggest that P ACAP38-positive cells are present within lymphoid tissues and may repr esent a lymphocyte-like cell subpopulation that has a potential role i n cell-to-cell interactions in the immune system and in the integrated communication between neuroendocrine and immune systems.