Characterization of immunoreactive insulin-like growth factor-I from leukocytes and its regulation by growth hormone.
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-derived 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-derived 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 bioactive irIGF-I from leukocytes and suggest a regulatory circuit for leukocyte-derived irGH and irIGF-I within the immune system.
Baxter
J B
JB
University of Alabama, Department of Physiology and Biophysics, Birmingham 35294-0005.
Blalock
J E
JE
Weigent
D A
DA
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004247:DNA; D005455:Fluorescent Antibody Technique; D013006:Growth Hormone / Q000378:metabolism / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D007962:Leukocytes / Q000166:cytology / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D012313:RNA / Q000378:metabolism; D011863:Radioimmunoassay
D012313:RNA; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D004247:DNA