Study of the immune complex precipitation-inhibiting capacity of sera of patients with chronic lymphocytic leukaemia.

Two procedures measuring the capacity of different sera to prevent the precipitation of nascent immune complexes were compared: a kinetic method with a constant immune complex/serum ratio and a new procedure--the increasing immune complex load method--using different immune complex/serum ratios. Immune complex precipitation inhibition is known to depend on complement. The sera of 25 patients with chronic lymphocytic leukaemia (CLL) and the sera of nine healthy blood donors were compared with the two procedures. The kinetic method discriminated poorly between the patients' sera and the control sera, whereas the increasing immune complex load method showed a highly significant difference between the two groups. Sera with low C4 level had the lowest immune complex precipitation-inhibiting activity. Interestingly, however, in the increasing immune complex load method not only hypocomplementaemic but also normocomplementaemic sera from CLL patients were found to be markedly defective. This finding suggests that the CLL patients' sera contain a factor which modulates complement-dependent inhibition of immune complexes.