Influence of fibrinogen fragments on human lymphocyte thymidine uptake

Fragments of human fibrinogen were tested for ability to suppress activation of human blood lymphocytes by the lectin phytohaemagglutinin (PHA). Measurement of cellular 14C-thymidine uptake was used as an indicator of DNA synthesis and cell proliferation. The tested fragments were obtained by plasmin digestion or by CNBr fragmentation of fibrinogen. Inhibition of uptake, with good dose response relationship, was demonstrated for the plasmic fragment PL-3 and for the CNBr fragment Hol-DSK. Digests of the latter with trypsin and plasmin gave the same effects as the intact fragment. However, reproducibility was poor with PL-3. Hol-DSK gave better reproducibility, but with pronounced interbatch variations. Other fragments of fibrinogen were tested, but gave no effect in the studied concentrations. The reason for the poor reproducibility is discussed.