Granulocyte release of vitamin B12-binders in vivo and in vitro in leukaemia and non-neoplastic leucocytosis.

The unsaturated vitamin B12-binding capacities of the 'large molecular size vitamin B12-binding protein' (LBP) and the 'small molecular size vitamin B12-binding protein' (SBP) were determined by a Sephadex G 150 gel filtration method in 9 patients with chronic myelocytic leukaemia (CML), 5 patients with blast cell leukaemia and 12 patients with non-neoplastic leucocytosis. EDTA plasma and serum separated after 20 min and after 120 min were examined. In the 20 min EDTA plasma samples, the mean LBP value was 8,009 pg/ml in CML, 2,468 in blast leukaemia, 175 in non-neoplastic leucocytosis, and 57 in normal controls. The in vitro release of LBP into serum was much smaller in the leukaemias than in non-neoplastic leucocytosis. No correlation was found between the LBP values and the white blood cell counts or lysozyme values, but lysozyme was correlated to white cell count in CML. It is suggested that the plasma LBP levels reflect the fraction of LBP decay taking place at sites, e.g. the spleen, from which the released LBP can enter the circulation.