This study used proteomic, biomechanical, and functional analyses to further define neutrophil heterogeneity in the context of SLE. Mass spectrometry proteomic and phosphoproteomic analyses were performed in healthy control normal density neutrophils (NDNs), SLE NDNs and in autologous SLE LDGs. Proteomic and phosphoproteomic differences were detected when comparing control to SLE neutrophils and when comparing SLE NDNs to SLE LDGs.