485 ROLE OP SOMATOMEDIN-C (SMC) IN LYMPHOCYTE PROLIFERATION

Abstract

As lymphocytes have receptors for SMC, we studied the role of SMC in lymphocyte proliferation. Peripheral lymphocytes from 27 controls and 17 children with growth hormone deficiency (GHD) were cultured in either autologous serum (AS) or pooled serum from normal adults (NS) with and without phytohemagglutinin(PHA). The mitogenic response (MR) was defined as thymidine incorporated in AS ÷ thymidine incorporated in NS. Control MR = 1.01 ± 0.05 (X ± SEM). Two different MRS were observed in the untreated GHD children. Most GHD sera had a normal MR (1.09 ± 0.06), but 4 had a very low MR (0.05 ± 0.02). MR did not correlate with SMC or growth rate. The two groups of children were similar in all other parameters that we measured. After 1 week of growth hormone treatment (0.1u/kg/d), MR was normal in all (0.97 ± 0.06). Partially purified SMC (10–500 ng/ml) did not increase MR in the presence of varying (0–5%) amounts of AS. Although PHA stimulated lymphocyte proliferation, culture medium SMC was not increased and was proportional to the SMC content of the serum used (r = 0.8). Conclusions: SMC does not have a direct role in lymphocyte proliferation since the MR in GHD serum was not proportional to SMC; exogenous SMC did not increase MR nor was SMC synthesized by lymphocytes in vitro. Serum from some GHD children lacks another factor(s) that supports lymphocyte proliferation in vitro.