EFFECTS OF HUMAN LYMPHOCYTE-CONDITIONED MEDIUM ON MG-63 HUMAN OSTEOSARCOMA CELL-FUNCTION

Lymphocytes are implicated in the pathogenesis of bone disease in chro nic inflammation, osteoporosis, transplantation and osteopetrosis. The effects of lymphocytes and lymphocyte-conditioned medium on bone-reso rbing activity and osteoclast function have been well studied, but the re are few studies of the effects of LCM on bone formation and osteobl ast function. The effects of LCM on the function of the MG-63 human os teosarcoma cell line were studied, which, when stimulated with 1,25-(O H)(2)D-3, demonstrates many of the properties of the mature human oste oblast. Lymphocytes contain oestrogen receptors and the model was also used to test the hypothesis that the effects of oestrogen on bone cel ls may be mediated indirectly via lymphokines. Lymphokines were measur ed by ELISA in human lymphocyte conditioned medium (LCM) collected fol lowing incubation of mixed lymphocytes with or without stimulation for 72 h. Unstimulated LCM increased proliferation of MG-63 cells and thi s increase was not affected by neutralization of interleukin 1 (IL-1), IL-3, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF) , tumour necrosis factor (TNF), lymphotoxin alpha, or interferon gamma (IFN-gamma). Phytohaemagglutinin-stimulated LCM decreased proliferati on of MG-63 cells, as well as induced expression of IL-6 mRNA, increas ed alkaline phosphatase production, and inhibited osteocalcin producti on. The decrease in proliferation was abolished by neutralization of I FN-gamma but was unaffected by neutralization of IL-1, IL-2, IL-3, IL- 4, IL-6, GM-CSF, TNF, or lymphotoxin alpha. Neutralization of IFN-gamm a in stimulated LCM also partially inhibited the increase in alkaline phosphatase production but had no effects on the decrease in osteocalc in production. Although oestrogen inhibited lymphocyte proliferation, the effects of LCM collected from lymphocytes in the presence of oestr ogen on MG-63 cell proliferation and function was no different than th e effects of LCM collected in the absence of oestrogen. LCM has multip le effects on MG-63 cell function and gene expression. Lymphocyte stim ulation during the preparation of LCM further modulates these effects. Although partially mediated by IFN-gamma, the effects of LCM on these cells cannot be completely explained by individual component lymphoki nes. This may have implications for understanding the pathophysiology of bone loss in inflammatory disorders as well as possible feedback lo ops of locally generated cytokines in bone. (C) 1998 Academic Press.