Neutrophil defense in patients undergoing bone marrow transplantation: Bactericidal/permeability-increasing protein (BPI) and defensins in graft-derived neutrophils

Background. Even after neutrophil counts return to near normal levels, patients undergoing myeloablative chemotherapy and bone marrow transplantation (BMT) are at risk for invasive bacterial infections, raising the possibility that their neutrophil function might be impaired. To assess potential qualitative defects in neutrophil function in patients undergoing BMT, we measured neutrophil content of the antimicrobial (poly)peptides BPI and defensins. Methods. Neutrophil extracts were analyzed for content of BPI by Western blotting and ELISA and for defensin peptides by acid-urea polyacrylamide gel electrophoresis (PAGE). Antibacterial activity of neutrophil extracts was measured against Escherichia coli K1/r, a clinical isolate sensitive to synergistic killing by BPI and defensins. Results. Neutrophil extract BPI content on post-BMT days +20, +30, and +100 (169+/-35, 232+/-57, and 160+/-55 ng per 10(6) neutrophils, respectively) was similar to the neutrophil BPI content of normal controls (163+/-35 ng per 10(6) neutrophils). Neutrophil defensin content also did not vary during this time-span. Activity of neutrophil extracts against E. coli K1/r did not differ between BAIT patients and controls. Conclusion. At post-BMT days +20 to +100, neutrophils derived from engrafted marrow contain normal quantities of BPI and defensins. Any deficiencies of neutrophil function during this phase are not due to inadequate expression of these antimicrobial (poly)peptides but could reflect abnormalities in other aspects of neutrophil function.