Eosinophil- and neutrophil-mediated injury of human lung fibroblast cells

The effect of culturing purified rat peritoneal neutrophils and eosinophils with the human foetal lung fibroblast cell line, MRC-5, was studied. Target cell damage was measured by the failure of the MRC-5 cells to form confluent monolayers during a 6-day incubation period. Neutrophils were more effective at inhibiting cell growth than were eosinophils with greater than 50% inhibition being recorded at initial effector: target cell ratios of 5:1 using neutrophils and 40:1 using eosinophils. Following stimulation with phorbol myristate acetate (PMA), one quarter the number of eosinophils was required to give 50% inhibition of cell growth. The addition of either catalase or superoxide dismutase partly reduced the activity of PMA-stimulated eosinophils, although only with catalase did this reach significance. PMA-stimulated neutrophils did not show any enhanced activity against the MRC-5 cells. Addition of the bacterial analogue f-Met-Leu-Phe (10(-7)M) was unable to increase the cytotoxic activity of eosinophils. Disrupted eosinophil suspensions were as effective as intact cells at inhibiting the growth of target cells whereas some loss in effectiveness was seen with disrupted neutrophils. Membrane-free supernatants from both eosinophils and neutrophils were inactive. The results suggest that although eosinophils and neutrophils are both capable of damaging lung fibroblast cells in culture, the latter is more effective, eosinophils appearing to require an additional stimulation in vitro. Possible mechanisms of cytotoxicity are discussed.