Twenty-three patients (10 males, 13 females, aged 4-16 years) with a clinical diagnosis of Henoch-Schonlein purpura were enrolled. Twenty healthy agematched children (10 males, 10 females) served as controls. TLR2 and TLR4 expression levels on peripheral blood mononuclear cells (PBMCs) were determined by flow cytometric analysis. PBMCs were cultured with heat shock protein (HSP) 60 (1 ƒÊg/ml) as an endogenous ligand for TLR.

Levels of TLR2 and TLR4 expression on PBMC were significantly lower in the Henoch- Schonlein purpura patients compared to healthy controls when stimulated with HSP60 and with lipopolysaccharide (LPS) (p<0.05 for both). There was no significant difference between the stimulated and unstimulated samples from the patients.

The lower TLR response to these ligands among these patients may reflect a tolerance to bacterial antigens. Further studies will clarify whether tolerance to microbial antigens may have a role in the pathogenesis and course of Henoch-Schonlein purpura Keywords : Henoch-Schönlein purpura, endotoxin tolerance, heat shock protein 60, Toll-like receptor 2, Toll-like receptor 4.