An investigation of factors influencing serum NCA (non-specific cross-reacting antigen) level in patients with chronic myeloid leukaemia.

The NCA (nonspecific cross-reacting antigen) was assayed in sera of patients with chronic myeloid leukaemia (CML). It was elevated to a mean value of 145·6 ng/ml (± 104·4 ng/ml) compared to 37·8 ng/ml (± 14·6 ng/ml) the sera of normal subjects. Patients with active disease generally had higher serum NCA levels than those with CML in blast crisis. A correlation of the serum NCA levels with the cellular contents of this antigen was attempted using different methods. Large variations of serum NCA levels were observed in different patients having roughly similar white blood cell (WBC) counts. In general a better correlation was observed between the serum NCA level and the number of maturing myeloid cells than with the number of polymorphs. The staining of blood smears with anti-NCA serum by an immunoperoxidase method suggested an explanation for some cases of CML in blast crisis with normal serum NCA levels inasmuch as the staining of myeloid cells was very weak or negative in these cases, indicative of a lack of NCA synthesis in the cells. In other cases, cellular NCA was measured by radioimmunoassay in maturing myeloid cells and polymorphs. The mean values were not significantly different from the NCA values obtained in normal polymorphs. From the NCA content/10(6) cells and the polymorph or maturing myeloid cell counts, we calculated the total NCA cell content/ml of blood. It was much higher than, though poorly correlated with, the serum NCA level. Thus factors other than NCA cellular content, mainly the rate of NCA release from the myeloid cells, might play an important role in the regulation of its serum level.