Serum amyloid A regulates granulomatous inflammation in sarcoidosis through Toll-like receptor-2.
BACKGROUND
The critical innate immune mechanisms that regulate granulomatous inflammation in sarcoidosis are unknown. Because the granuloma-inducing component of sarcoidosis tissues has physicochemical properties similar to those of amyloid fibrils, we hypothesized that host proteins capable of forming poorly soluble aggregates or amyloid regulate inflammation in sarcoidosis.


OBJECTIVE
To determine the role of the amyloid precursor protein, serum amyloid A, as an innate regulator of granulomatous inflammation in sarcoidosis.


METHODS
Serum amyloid A expression was determined by immunohistochemistry in sarcoidosis and control tissues and by ELISA. The effect of serum amyloid A on nuclear factor (NF)-kappaB induction, cytokine expression, and Toll-like receptor-2 stimulation was determined with transformed human cell lines and bronchoalveolar lavage cells from patients with sarcoidosis. The effects of serum amyloid A on regulating helper T cell type 1 (Th1) granulomatous inflammation were determined in experimental models of sarcoidosis, using Mycobacterium tuberculosis catalase-peroxidase.


RESULTS
We found that the intensity of expression and distribution of serum amyloid A within sarcoidosis granulomas was unlike that in many other granulomatous diseases. Serum amyloid A localized to macrophages and giant cells within sarcoidosis granulomas but correlated with CD3(+) lymphocytes, linking expression to local Th1 responses. Serum amyloid A activated NF-kappaB in Toll-like receptor-2-expressing human cell lines; regulated experimental Th1-mediated granulomatous inflammation through IFN-gamma, tumor necrosis factor, IL-10, and Toll-like receptor-2; and stimulated production of tumor necrosis factor, IL-10, and IL-18 in lung cells from patients with sarcoidosis, effects inhibited by blocking Toll-like receptor-2.


CONCLUSIONS
Serum amyloid A is a constituent and innate regulator of granulomatous inflammation in sarcoidosis through Toll-like receptor-2, providing a mechanism for chronic disease and new therapeutic targets.
Chen
Edward S
ES
Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Song
Zhimin
Z
Willett
Matthew H
MH
Heine
Shannon
S
Yung
Rex C
RC
Liu
Mark C
MC
Groshong
Steve D
SD
Zhang
Ying
Y
Tuder
Rubin M
RM
Moller
David R
DR
D000328:Adult; D000818:Animals; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005260:Female; D005434:Flow Cytometry; D006099:Granuloma / Q000276:immunology / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D008168:Lung / Q000737:chemistry / Q000473:pathology; D008297:Male; D051379:Mice; D008875:Middle Aged; D016328:NF-kappa B / Q000502:physiology; D011014:Pneumonia / Q000276:immunology / Q000503:physiopathology; D051381:Rats; D017565:Sarcoidosis, Pulmonary / Q000276:immunology* / Q000473:pathology / Q000503:physiopathology; D000685:Serum Amyloid A Protein / Q000032:analysis / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D051195:Toll-Like Receptor 2 / Q000502:physiology*
D016328:NF-kappa B; D000685:Serum Amyloid A Protein; C495342:TLR2 protein, human; D051195:Toll-Like Receptor 2