Interleukin‐2 prevention of apoptosis in human neutrophils

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Abstract
Evidence is presented that interleukin (IL)‐2 maintains viability of human polymorphonuclear cells (PMN) in culture by preventing these cells from undergoing programmed cell death (PCD) and induces the synthesis of new RNA and protein. Our laboratory has recently discovered that human PMN constitutively express IL‐2β receptor and more importantly, PMN are able to respond functionally to IL‐2 by enhanced growth inhibitory activity against an opportunistic fungal pathogen, Candida albicans. We now report that IL‐2 was able to interfere with the PCD process and reduce the number of apoptotic PMN to < 40% in 72‐h culture. Freshly isolated PMN usually underwent a timedependent aging process and > 80% of PMN cultured in medium alone for 72 h showed morphologic features of PCD as depicted by hematoxylin and eosin staining as well as by electron microscopy. During the PCD process, untreated PMN not only exhibited condensed nuclear structure and decrease in cell size, but also displayed DNA fragmentation. DNA fragmentation in PMN was prevented by IL‐2. Prevention of PCD by IL‐2 was associated with an increase in new RNA and protein synthesis in PMN, which may reflect cytokine induction, such as tumor necrosis factor, as we have recently shown. Thus, our data expands our current understanding of PMN in that they may be an active component of the immune system, with a longer life‐span when activated than expected.