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GH is an immunomodulatory factor that can be synthesized and secreted by mononuclear leukocytes. To determine if GH can be produced by the human immune system, we assessed the presence of GH messenger RNA (mRNA) in both normal and abnormal human lymphoid tissues by RT-PCR and nonisotopic in situ mRNA hybridization. The predicted PCR product of 16lbp from human thymus, spleen, tonsil, lymph node, thymoma, and T and B cell lymphomas was similar to the product amplified from the human pituitary. Restriction enzyme digestion confirmed that complementary DNA generated using GH primers originated from GH mRNA. Furthermore, we performed in situ hybridization to localize the GH mRNA-positive cells. A hybridization signal for GH mRNA was found in all tissues examined. The distribution patterns of GH in normal lymphoid tissues suggested that GH can be produced by lymphocytes, as well as endothelial cells and other cell types. Also, GH mRNA-positive cells were distributed diffusely throughout T and B cell lymphomas and a thymoma. Our results demonstrate GH gene expression in normal and neoplastic human lymphoid tissues including nonlymphoid cells. This finding supports the hypothesis that the human immune system is an extrapituitary site of GH gene expression that may serve as an autocrine/paracrine factor in immunomodulation.
Wu et al. (Fri,) studied this question.