Fungicidal activity of human peripheral blood leukocytes against Paracoccidioides brasiliensis yeast cells

Although epidemiological findings suggest that normal humans are resistant to Paracoccidioides brasiliensis infection, the host defense mechanisms against this fungus have not been fully understood. Here we examined human leukocytes for antifungal activity against yeast cells of this fungus, using an improved mycological culture medium with high plating efficiency for the yeast cell. In an attempt to minimize the impairment of leukocyte activities during the isolation process, leukocytes removed by centrifugation from a buffy coat of peripheral blood were used in the antifungal assay without further fractionation. The leukocytes thus prepared effectively killed P. brasiliensis yeast cells within the first 4 h of co-culture. Adding interferon-gamma (37 ng/ml), granulocyte-macrophage colony-stimulating factor (5 ng/ml), interleukin (IL)-1beta (12 ng/ml), or IL-4 (12 ng/ml) to the assay system enhanced the leukocyte antifungal (growth inhibitory) activity by 48 h. By contrast, addition of IL-8 (50 ng/ml) impaired the leukocyte activity. Tumor-necrosis factor-alpha (50 ng/ml) or IL-10 (25 ng/ml) had no effect in this respect. Dexamethasone (1 micromol/l) reduced the antifungal activity of leukocytes. This is the first demonstration that human leukocytes are able to effectively kill yeast cells of P. brasiliensis.