Insulin-like growth factor secretion by human B-lymphocytes: a comparison of cells from normal and pygmy subjects.

Freshly isolated human B-lymphocytes from eight subjects and Epstein-Barr virus-transformed human B-lymphocytes from seven subjects were examined for their capacity to secrete insulin-like growth factor-I (IGF-I) and IGF-II and for their capacity to respond to human GH. Similar studies were conducted with Epstein-Barr virus-transformed lymphocytes collected from six African pygmies. When transformed B-lymphocytes from normal stature subjects were cultured for 3 weeks in RPMI-1640 medium (6 x 10(3) cells/75-cm2 flask at seeding), significant amounts of IGF-I, but no IGF-II, were produced. GH (150 ng/mL) significantly increased for control cells the amount of IGF-I produced at each sampling interval compared to that by unstimulated cultures (P less than 0.05 at 1 week; P = 0.005 at 3 weeks). At 3 weeks, cell counts of cultures compared were 4.13 +/- 0.39 X 10(6)/mL for unstimulated cells and 4.23 +/- 0.87 X 10(6)/mL for GH-stimulated cells. IGF-I production at this time interval by unstimulated cells was 2.8 +/- 2.3 ng/mL, and that by GH-stimulated cells was 12.3 +/- 2.5 ng/mL (P = 0.005). Cell multiplication rates of control cultures were increased in 1 week by GH stimulation [GH stimulated, [16.7 +/- 22.0 X 10(4) cells, unstimulated, 5.73 +/- 4.1 X 10(4) cells; (mean +/- SD); n = 14; P less than 0.01]. Similar results occurred with GH studied at a lower concentration of 10 ng/mL for 3 weeks. Freshly isolated B-lymphocytes did not secrete IGF-I and II after 5 days of culture with GH. Cultures established from cells derived from pygmies produced significantly less IGF-I (4.24 +/- 2.62 ng/mL) when stimulated with 150 ng/mL GH than cultures of cells from normal stature subjects (12.3 +/- 2.5 ng/mL; 0.005 less than P less than 0.01). The cultures compared had a similar cell density. A similar significant difference in IGF-I secretion occurred between cultures of pygmy and control cells stimulated with 10 ng/mL GH. These data are consistent with previous in vivo studies in which pygmies failed to increase IGF-I and exhibit metabolic responses to exogenous GH.