Inhibition of human T lymphocyte proliferation in vitro by commercial factor VIII concentrates.

Several investigators recently described a T lymphocyte subset abnormality (reversed helper/suppressor cell ratio) in haemophiliacs, especially following previous substitution therapy. We studied in vitro the potential effects of two commercial factor VIII concentrates on incorporation of 3H-thymidine by isolated human peripheral blood lymphocytes after stimulation with either phytohaemagglutinin or monoclonal antibody OKT3. Dose-related inhibition of thymidine incorporation was found for both concentrates but none using the purified main protein constituents, i.e. factor VIII, fibrinogen or fibronectin. Furthermore, the 'inhibitor' was completely removed by dialysis.