GROWTH HORMONE RECEPTOR (GH-R) ON PERIPHERAL BLOOD LYMPHOCYTES (PBL): HIGH LEVEL OF EXPRESSION ON BLYMPHOCYTES (L)

Abstract

Although the GH-R is known to be expressed on a variety of cells, among the immune cells it has been detected on IM9 (human plasmocytoma cell line) and PBL by binding studies with ¹²⁵ I-GH. This method does not allow to accurately determine which L subset expresses the receptor. Incomplete knowledge of the GH-R distribution among L subsets makes an understanding of the mechanism of action of GH on the immune system difficult. Using a fluorescein-conjugated, GH-R specific monoclonal antibody (mAb 263) in a direct immunofluorescence assay, it was observed that the antibody binds to all L. However, a small subset of PBL binds the anti GH-R mAb with high affinity. Using the conjugated mAb 263 along with different phycoerytrin-conjugated mAbs specific for T, T4, T8, Natural Killer and B cells, this small subset was identified as B cells. The binding of mAb 263 to the different L subsets was quantified in 7 donors. The number of GH-R/cell in each subset was expressed relative to T cells (CD2+ cells). B cells express GH-R 2.58±0.51 fold higher than T cells (p<0.05). The GH-R in the other subsets did not differ from that of T cells. Scatchard analysis of the binding to T and B cells showed that B cells express approximately 4000 GH-R/cell vs. the 1500 GH-R/cell found in T cells. The dissociation constant was identical.

Although the significance of this finding is uncertain, it has been hypothesised that high concentrations of GH result in a suppressive effect of the hormone by disunion of GH-R dimers into monomers. GH may have differential effects on specific cell subsets based not only on its concentration, but on GH-R density as well. GH seems to have specific targets among L and the regulation of their activation and function could be important in the child during phases of rapid growth.

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