Suppressive activity of neutrophils requires degranulation. (A-B) Neutrophils were stimulated with the indicated stimuli for 4 hours at 37°C after which supernatants were harvested and analyzed for the presence of myeloperoxidase (from primary granules) (A) and lactoferrin (from secondary granules) (B) by enzyme-linked immunosorbent assay (n = 7). (C-F) Purified T cells from control donors (C,E; n = 2), FHL-5 (D; n = 2), or MPO-deficient (F; n = 1) patients were cultured with anti-CD3 and anti-CD28 antibodies (red bars), in the presence of neutrophils from control donors (blue bars), FHL-5 patients (C-D, green bars), or an MPO-deficient patient (E-F, green bars), and/or indicated stimuli. Cells were harvested after 4 to 6 days and analyzed by flow cytometry for CFSE dilution among CD4⁺ T cells. Error bars indicate SEM. ***P < .001; **P < .01; *P < .05. CytoB, cytochalasin B; pt, patient.