What's wrong with neutrophils in lupus?

Polymorphonuclear neutrophils (PMNs) act by promoting phagocytosis, and are regarded as the first line of defense against pathogen invasion. However, recent investigations have revealed that they have many previously unknown functions. These functions include mitogen-induced cell-mediated cytotoxicity, production of cytokines/chemokines/growth factors, and release of neutrophil extracellular traps (NETs) and ectosomes/exosomes. Membrane exchange (trogocytosis) is also noted following direct cell-cell contact with other immune cells for modulating innate and adaptive immune responses. These observations strongly suggest that neutrophils may play an important role in the immune network. Systemic lupus erythematosus (SLE) is a prototype of systemic autoimmune diseases characterised by the production of diverse antigen-driven autoantibodies against intra- and extracellular molecules. Multiple immune dysfunctions have been reported in SLE patients. These include excessive interferon alpha (IFN-α) expression, aberrant cytokine/chemokine/growth factor production, skewing of T cell immune responses toward Th2 and Th17 pathways, polyclonal B cell activation, increased apoptosis and NET formation, defective clearance of cell debris and NET-related molecules, and abnormal ectosome/exosome release in the plasma. We have demonstrated that SLE-PMNs per se exhibit aberrant cytokine/chemokine expression, defective glucose metabolism, and increased mitochondrial DNA D310 heteroplasmy with reduced redox capacity. Our data also indicate that autoantibodies purified from SLE sera disrupt PMN functions. In the present review, we discuss these abnormalities in detail and attempt to elucidate the potential roles of disrupted PMN functions in lupus pathogenesis.