Abstract
Serum from patients with juvenile chronic arthritis (JCA) was shown to inhibit colony formation by normal erythropoietic progenitor cells cultured in vitro. The inhibition was proportional to the degree of anaemia and to certain indices of activity of the arthritis and systemic disease. It occurred in a dose dependent manner with increasing serum concentration and was independent of previous blood transfusion or administered drugs. Erythropoietic progenitor cells from the bone marrows of anaemic patients with JCA showed normal requirements for accessory cells (T lymphocytes and macrophages) in culture, and autologous accessory cells were not deficient in providing normal growth requirements.