IgG from Patients with Autoimmune Disease Activates Neutrophils

Abnormalities in neutrophil function play a role in autoimmune rheumatic diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Data also suggest immunoglobulin G (IgG) may be important in immunopathology, thus, many researchers have sought to better understand the interaction between IgG and neutrophils.

New data reveal a different pattern of neutrophil activation in SLE patients than in RA patients. Moreover, different autoimmune diseases have distinct patterns of IgG-mediated integrin activation and neutrophil function, which may explain disease-specific differences in vascular damage and dysfunction. Akif A. Khawaja, PhD, a research associate at University College, London, U.K., and colleagues say the research, published online in Scientific Reports, points toward novel approaches to develop new therapies.¹

The investigators isolated neutrophils from 12 healthy controls, 12 SLE patients and seven RA patients. They evaluated the differences between the isolated neutrophils of each group, finding that SLE neutrophils had significantly lower rates of hydrogen peroxide (H₂O₂) production than healthy control neutrophils and RA neutrophils. Additionally, they found IgG more readily bound the neutrophils of SLE and RA samples than it did the neutrophils of healthy controls. Having established the difference in binding, the investigators next sought to determine if IgG modulated β₁ or β₂ integrin-mediated adhesion.

“Our experiments utilized immobilized fibronectin and fibrinogen, which are found in areas of tissue injury with local activation of coagulation and in regions of vascular endothelial damage where the sub-endothelial basement membrane has been exposed,” write the authors in their discussion. “Our choice of ligands has the advantage of readily allowing us to distinguish the effects of IgG on β₁-mediated adhesion to ECM/VCAM-1 from the effects on α_Mβ₂-mediated adhesion.”

The researchers found that, although both RA-IgG and SLE-IgG increased PMA-induced β₁ integrin-mediated adhesion to fibronectin, only SLE-IgG enhanced α_Mβ₂ integrin-mediated adhesion to fibrinogen.

Next, the researchers examined the modulatory effects of IgG samples from the different groups on unstimulated and PMA-induced adhesion to human umbilical cord endothelial cells. They found SLE IgG significantly enhanced both unstimulated and PMA-induced neutrophil adhesion to human umbilical cord endothelial cells.

“Integrin activation is central to leukocyte migration, therefore, we examined whether autoimmune rheumatic disease-IgG affected neutrophil adhesion to, and migration across, the endothelium,” write the authors. “Interestingly, SLE IgG, but not RA IgG, significantly augmented neutrophil adhesion to [human umbilical cord endothelial cells], while migration across an IL-8 gradient was unaffected by [autoimmune rheumatic disease]-IgG.”

The investigators then turned their attention to characterizing the ability of IgG to modulate the release of extracellular DNA and found both SLE and RA IgG caused unstimulated neutrophils to increase reactive oxygen species generation and DNA externalization. Specifically, neutrophils cultured in the presence of SLE or RA IgG spontaneously released more DNA than neutrophils cultured with healthy control IgG. However, co-culture with resting endothelium prevented IgG-mediated increase of extracellular DNA. That said, in the case of SLE IgG, the inhibition could be overcome by stimulating the endothelium with TNF-α.