Antineutrophil cytoplasm antibody (ANCA)–associated
vasculitis (AAV) commonly results in glomerulonephritis, in
which neutrophils and monocytes have important roles.
The heterodimer calprotectin (S100A8/S100A9, mrp8/14)
is a Toll-like receptor-4 ligand found in neutrophils and
monocytes and is elevated in inflammatory conditions. By
immunohistochemistry of renal biopsies, patients with focal
or crescentic glomerular lesions were found to have the
highest expression of calprotectin and those with sclerotic
the least. Serum levels of calprotectin as measured by ELISA
were elevated in patients with active AAV and the levels
decreased but did not normalize during remission,
suggesting subclinical inflammation. Calprotectin levels in
patients with limited systemic disease increased following
treatment withdrawal and were significantly elevated in
patients who relapsed compared with those who did not. As
assessed by flow cytometry, patients with AAV had higher
monocyte and neutrophil cell surface calprotectin expression
than healthy controls, but this was not associated with
augmented mRNA expression in CD14þ monocytes or
CD16þ neutrophils. Thus, serum calprotectin is a potential
disease biomarker in patients with AAV, and may have a role
in disease pathogenesis.