Expression of Toll-Like Receptor-2 and -4 in Normal Human Valves and Dysregulated Expression in Valves from Rheumatic Heart Disease Patients

Abstract

Toll-Like Receptors (TLRs) critically link innate immunity with adaptive immunity by recognising membrane components of microorganisms and inducing an inflammatory response. TLRs1-9 have been shown to be expressed in human aortic VICs with TLR2 and TLR4 upregulated in calcified human leaflets.  We hypothesise dysregulation of TLR2 and TLR4 in patients with rheumatic heart disease (RHD). 6 normal human aortic and mitral leaflets, 6 aortic and mitral leaflets from RHD and 5 calcified human aortic leaflets were analysed by immunohistochemistry for the spatial expression of TLR2 and TLR4. Flow cytometry assessed expression levels of TLR2 and TLR4, in VIC and VECs, after treatment with bacterial peptides. RHD aortic leaflets showed a significantly reduced expression of TLR4 (p=0.0007) compared to normal and calcified aortic leaflets (p=0.0095). RHD aortic leaflets showed a significantly reduced expression of TLR2 (p=0.0087) compared to normal and calcified aortic leaflets (p=0.0043). Mitral RHD leaflets showed a similar pattern to aortic RHD leaflets in that they showed significantly reduced level of expression of TLR4 (p=0.029) and TLR2 (p=0.0087) compared to normals. Lipoteich acid decreased whereas lipopolysaccharide (LPS) increased the incidence of TLR4+ve VICs. LPS treatment decreased the incidence of TLR2+ve VECs. A significantly reduced expression of TLR2 and TLR4 in aortic and mitral leaflets from RHD patients suggests there may be a compensatory mechanism in RHD patients to limit inflammation. Additional factors that reduce the expression of TLR2 and TLR4 in human VICs and VECs are being investigated.