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Characterization of Immunoreactive Insulin-Like Growth Factor-I from Leukocytes and Its Regulation by Growth Hormone^*

University of Alabama at Birmingham, Department of Physiology and Biophysics Birmingham, Alabama 35294-0005

Address all correspondence and requests for reprints to: Dr. Douglas Weigent, University of Alabama at Birmingham, Department of Physiology and Biophysics, UAB Station, BHSB 894, Birmingham, Alabama 35294-0005.

Abstract

In the present study, we investigated the production of insulin-like growth factor I (IGF-I) by leukocytes and its production after treatment with GH. Immunoreactive (ir) IGF-I was observed in leukocytes by direct immunofluorescence with fluorescein isothiocynate-conjugated antibodies to IGF-I. Studies using immunoaffinity purification, HPLC and a fibroblast proliferation bioassay suggests that the de novo synthesized leukocyte-derived irIGF-I is similar in mol wt, antigenicity, and bioactivity to serum IGF-I. We also evaluated the effect of GH on the production of leukocyte-derived irIGF-I, Spleen cells cultured for 24 h in the presence of exogenous GH caused a 2- fold elevation of irIGF-I as demonstrated by RIA and immunofluorescence. In order to determine if leukocyte-de rived irGH can stimulate the production of irIGF-I, we cultured spleen cells for 24 h in the presence of antibodies specific for GH. The data showed a decrease in the number of cells positive for irIGF-I, suggesting that leukocyte-de rived irGH may stimulate the synthesis of irIGF-I by leukocytes. We also demonstrated that exogenous IGF-I can decrease the levels of leukocyte GH-related RNA and ir protein. Taken together, our data demonstrate the synthesis and secretion of bioaetive irIGF-I from leukocytes and suggest a regulatory circuit for leukocyte-de rived irGH and irIGF-I within the immune system, (Endocrinology 129: 1727–1734, 1991)

Footnotes

^* This work was supported in part by NINCD Grant ROl-NS-24636 and NIDDK Grant R02-DK-38024.

Received March 18, 1991.

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