Light chain composition of serum granulocyte binding immunoglobulins.

Serum granulocyte binding IgG, IgM, and the light chain composition of granulocyte binding immunoglobulins were measured in 58 adult subjects, including 8 normal individuals, 6 with Felty syndrome, 6 with chronic idiopathic neutropenia, 32 with B-cell chronic lymphocytic leukemia (CLL), and 6 with multiple myeloma. An abnormal kappa/lambda ratio of granulocyte binding immunoglobulins was detected in 12 of 32 patients with CLL. Neutropenia in patients with CLL did not correlate with an abnormal kappa/lambda ratio or excess granulocyte binding IgG, but did correlate with granulocyte binding IgM (P less than 0.02). Eight of the 12 patients (5 with chronic idiopathic neutropenia and 3 with Felty syndrome) with an immune neutropenia without underlying neoplastic disorder had light chain restricted granulocyte binding immunoglobulins. Of all patients' sera with light chain restriction, 76% were of lambda light chain isotype. Thus, the frequent detection of light chain restriction of granulocyte binding immunoglobulins is not a reflection of malignancy but is suggestive of the somatic mutation of immunoglobulin light chain genes.