Role of myeloperoxidase in respiratory burst of human polymorphonuclear leukocytes

Abstract

A comparative study of the respiratory burst [monitored as superoxide (O₂ ⁻) production] of normal and myeloperoxidase (MPO) -deficient poiymorphonuclear leukocytes (PMNs) was carried out on 11 MPO-deficient subjects that represent the largest sample of this kind ever studied. The rate of O₂ ⁻ production by isolated PMNs and whole blood from normal and MPO-deficient subjects was comparable during the initial 30–40 min of incubation with serum-treated zymosan (STZ). Afterwards, the amount of O₂ ⁻ produced became progressively higher in MPO-deficient cells at least until 120 min incubation with STZ. On the contrary the rate of O₂ ⁻ production by both cell types in response to 4-β-phorbol-12-myristate-13-acetate (PMA) was the same. The PMNs of four MPO-deficient subjects were tested for their ingestion ability by counting the number of ingested particles on toluidine blue-stained sections of epoxy-embedded PMN suspensions. Both cell types ingested STZ particles at a comparable rate at early postphagocytic times, whereas on prolonged incubation MPO-deflcient PMNs ingested more STZ particles than normal PMNs. These results suggest that the ingestion capacity of normal cells may undergo a more rapid deterioration than that of MPO-deficient cells during incubation with STZ. Evidence for a higher deterioration of normal PMNs with respect to MPO-deficient PMNs was obtained also from studies on the effect of storage on O₂ ⁻ generation. After standing at melting ice temperature for 3 h, normal PMNs produced less O₂ ⁻ than MPO-deficient PMNs in response to PMA, and the difference in O₂ ⁻ production by the two cell types in response to STZ was evident at earlier postphagocytic periods than with freshly isolated cells. Taken all together these results suggest that normal PMNs and MPO-deficient PMNs do not intrinsically differ in O₂ ⁻ generating potential and that the difference in the respiratory burst observed during phagocytosis may be accounted for by a more marked deterioration, in normal PMNs, of one or more functions related to the respiratory burst.