Augmentation of the neutrophil response to Naegleria fowleri by tumor necrosis factor alpha.

Conditioned medium from phytohemagglutinin-stimulated human mononuclear leukocytes, previously shown to activate neutrophils for amoeba killing, was found to contain high levels of tumor necrosis factor alpha (TNF-alpha) by an enzyme-linked immunosorbent assay. The effects of human recombinant TNF-alpha on the response of human neutrophils to the pathogenic free-living amoeba Naegleria fowleri was studied in vitro. The data showed that recombinant human TNF-alpha augmented the neutrophil respiratory burst (assessed by the cytochrome c reduction assay and lucigenin-dependent chemiluminescence assay) in response to amoebae opsonized with human serum. The priming effects of TNF-alpha were transient; marked enhancement was found with short 5- to 30-min preincubations of neutrophils with the cytokine. The enhancement of oxygen radical production was evident with 20 U of TNF-alpha per 10(6) neutrophils and continued to increase with up to 100 U. TNF-alpha also augmented the neutrophil lysosomal enzyme release in response to N. fowleri. The results support previous reports suggesting an important role of neutrophil cytokine activation for effective immunity against free-living amoebae.