Vasopressin is located within lymphocytes in the rat spleen

Using dual antigen immunocytochemical staining with a specific antiserum for arginine vasopressin (AVP), we have detected AVP immunoreactivity in clusters of large immunoglobulin (Ig) G-containing cells, probably plasma cells, within the rat spleen, and in smaller cells which are IgG-negative. Vasopressin-positive cells were detected principally throughout the white pulp areas in the subcortical region of the spleen. IgG staining could only be detected within the cells and not on the cell surface, demonstrating that the antiserum is recognising genuine intracellular IgG and not cell surface antigens. Reversed-phase HPLC of spleen tissue extract revealed a single peak of AVP immunoreactivity which co-eluted with the standard. This is the first evidence that AVP is found within lymphocytes of the immune system and provides further information about the important interaction between the endocrine and immune systems.