Impaired neutrophil function and myeloperoxidase deficiency in myeloid metaplasia.

The ability of neutrophils to phagocytose and kill Candida guilliermondii was investigated in 12 patients with myeloid metaplasia (MM). Following ingestion there was a considerable impairment in the ability of MM neutrophils to kill and digest Candida which was not explained by the very mild impairment in phagocytosis. Quantitative myeloperoxidase measurement revealed an overall deficiency of this enzyme in MM neutrophils and a highly significant correlation between low myeloperoxidase levels and impaired candidacidal activity. Neutrophils from patients with myeloid metaplasia show a pattern of defective microbial killing, high alkaline phosphatase activity and low myeloperoxidase activty which is similar to that seen in severe infections and distinct from chronic granulocytic leukaemia. The cells of one patient with particularly low myeloperoxidase and defective microbial killing were further studied both cytochemically and by electron microscopy. The azurophilic granules of his neutrophils were present in normal numbers and contained normal amounts of acid phosphatase but they lacked myeloperoxidase.