Endotoxin up-regulates interleukin-18: potential role for gram-negative colonization in sarcoidosis.
OBJECTIVE
Sarcoidosis is a granulomatous disease of unknown etiology characterized by a helper T-cell type 1-mediated process. Previously we demonstrated a role for interleukin-18 in sarcoidosis. Here we examine the regulation of interleukin-18 in this condition.


METHODS
Cytokine levels in sarcoid epithelial lining fluid were measured by ELISA. We examined interleukin-18 promoter activity and mRNA and protein levels in the epithelial lining fluid of individuals with active sarcoidosis, and of individuals recovered from sarcoidosis, in response to purified protein derivative of Mycobacterium tuberculosis, beryllium sulfate, zirconium sulfate, aluminum sulfate, and lipopolysaccharide. Endotoxin levels in the epithelial lining fluid of individuals with sarcoidosis, individuals recovered from sarcoidosis, and control subjects were assessed by Limulus amebocyte lysate analysis. Allele-specific polymerase chain reaction was used to genotype 94 patients with sarcoidosis and 97 control subjects for the interleukin-18 -607(A/C) polymorphism. Species-specific polymerase chain reaction identified bacterial DNA in fluid samples.


RESULTS
Epithelial lining fluid from active sarcoids contained elevated levels of interleukin-18, interferon-gamma, and interleukin-12 compared with recovered patients and also contained significantly higher levels of endotoxin. Depletion of endotoxin from this epithelial lining fluid reduced its effect on the human interleukin-18 promoter in vitro. There was a higher frequency of the -607C allele and -607(C/C) genotype in the sarcoidosis population compared with control subjects; however, this was not associated with a functional response to endotoxin treatment. Finally, bacterial 16S rRNA from Haemophilus influenzae and Moraxella catarrhalis was detected in sarcoid fluid samples.


CONCLUSIONS
The pathogenesis of sarcoidosis is propagated through the actions of a helper T-cell type 1-driven response. This study shows that gram-negative bacteria may contribute to this effect by upregulating interleukin-18 expression.
Kelly
Deirdre M
DM
Respiratory Research Division, Department of Medicine, Royal College of Surgeons in Ireland, Education and Research Centre, Beaumont Hospital, Dublin 9, Ireland.
Greene
Catherine M
CM
Meachery
Gerard
G
O'Mahony
Michael
M
Gallagher
Paula M
PM
Taggart
Clifford C
CC
O'Neill
Shane J
SJ
McElvaney
Noel G
NG
D000328:Adult; D001992:Bronchoalveolar Lavage Fluid; D005260:Female; D006090:Gram-Negative Bacteria / Q000502:physiology*; D006801:Humans; D020382:Interleukin-18 / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D012336:RNA, Ribosomal, 16S / Q000032:analysis; D017565:Sarcoidosis, Pulmonary / Q000382:microbiology / Q000503:physiopathology*; D006377:T-Lymphocytes, Helper-Inducer / Q000502:physiology; D014373:Tuberculin / Q000494:pharmacology; D015854:Up-Regulation / Q000502:physiology
D020382:Interleukin-18; D008070:Lipopolysaccharides; D012336:RNA, Ribosomal, 16S; D014373:Tuberculin