Expression and localization of prolactin messenger ribonucleic acid in the human immune system.

Pituitary PRL is involved in immunoregulation. Also, a PRL-like molecule is secreted by peripheral blood mononuclear cells. In this study, we examined tissues of the human immune system to evaluate if the PRL gene is expressed and to determine the location and type of cells involved in its synthesis. To evaluate the expression of PRL messenger RNA (mRNA) in normal and abnormal human lymphoid tissues, we used RT-PCR to generate a specific 276-bp product from normal human thymus, spleen, tonsil, lymph node, and lymphoid tumors. Restriction enzyme digestion confirmed that this PCR product was expressed PRL. Furthermore, we developed a specific and sensitive nonisotopic in situ hybridization technique for PRL mRNA, and cells containing PRL mRNA were found in each tissue of the human immune system. Also, PRL mRNA was widely distributed throughout neoplastic tissue from a thymoma and lymphomas where mitogenic and anti-apoptotic properties of PRL could be involved in tumor progression. PRL mRNA was localized in lymphocytes, epithelial cells, and vascular endothelial cells. The presence of PRL mRNA in vascular endothelium cells suggests other roles for PRL in these tissues in addition to immunomodulation. In conclusion, the presence of PRL mRNA in human lymphoid tissue implies that locally synthesized PRL may play a critical role in immunocompetence by providing an important regulatory signal to the microenvironment of human lymphoid organs.