IgG from anti-MDA5⁺ CADM patients impairs NK cell function via CD16 in RP-ILD

To investigate natural killer (NK) cell dysfunction in anti-MDA5 autoantibody-positive (anti-MDA5⁺) clinically amyopathic dermatomyositis (CADM) patients with rapidly progressive interstitial lung disease (RP-ILD), and explore potential mechanisms related to macrophage activation.

Differentially expressed genes (DEGs) in peripheral blood mononuclear cells (PBMCs) from anti-MDA5⁺ CADM and anti-Jo1-positive (anti-Jo-1⁺) dermatomyositis patients were profiled using the Illumina HT-12 v4 chip. Cytokine profiles were analyzed using ELISA, and flow cytometry was performed to assess PBMC subsets, NK cell cytotoxicity, and the activation of PLC-γ2 and MAPK signaling. IgG purified from patient serum was used to assess antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP) in THP-1/THP-1-like macrophages under poly(I:C) stimulation.

Anti-MDA5⁺ CADM patients exhibited downregulated expression of NK cell activation receptor genes and elevated cytokines such as sCD163 and ferritin compared to anti-Jo-1⁺ patients. NK cell percentages in PBMCs were prominently decreased in anti-MDA5⁺ patients with RP-ILD compared to those without, and NK cell cytotoxicity or degranulation was weakened, as shown by decreased CD107a and perforin expression, while monocyte populations were increased in RP-ILD patients. IgG purified from anti-MDA5⁺ patient serum impaired NK-cell degranulation in vitro and enhanced ADCC/ADCP activity of THP-1 macrophages following poly(I:C) stimulation. These effects were reduced by CD16 knockdown, indicating involvement of FcγRIII (CD16) dependent interactions. PBMCs from RP-ILD patients exhibited hypophosphorylation of PLCγ2 and ERK, along with hyperphosphorylation of p38, consistent with altered downstream signaling associated with CD16 engagement.

NK-cell dysfunction and enhanced macrophage activation in anti-MDA5⁺ CADM patients with RP-ILD are associated with dysregulated CD16-dependent IgG-cell interactions and perturbations in downstream PLCγ2-MAPK signaling. These findings highlight FcγR-mediated immune dysregulation as a potential contributor to the severe inflammatory phenotype characteristic of RP-ILD, while not establishing antigen-specific mechanisms.