Stronger Toll-like receptor 1/2, 4, and 7/8 but less 9 responses in peripheral blood mononuclear cells in non-infectious exacerbated asthmatic children

Toll-like receptors (TLR) initiate innate and often affect adaptive immune response. This study aimed to determine if TLR response and T regulatory cell (Treg) function in peripheral blood mononuclear cells (PBMC) correlate with clinical severity in non-infectious asthma. TLR1-9 expression and representative response cytokine TNF-α, IL-6, and IFN-β secretions were analyzed after stimulation by TLR1-9 ligands from 17 non-infectious asthmatic children. TNF-α production was higher in TLR1/2 (median 385.4 vs. 250.3pg/ml in 1μg/ml Pam3CSK4, p=0.0078), TLR4 (2392.4 vs. 1355.9 in 1μg/ml LPS; p=0.0005), and TLR7/8 (10,776.2 vs. 4237.0pg/ml in 1μg/ml R848, p=0.0079) of patients in exacerbation than those in convalescence and healthy controls despite equal TLR expression. TNF-α production stimulated by TLR9 agonist was significantly lower in exacerbation (17.7 vs. 34.9pg/ml in 1μg/ml ODN2216, p=0.0175), while IL-6 production had similar patterns but was significantly lower in TLR3 signaling (119.7 vs. 245.0pg/ml in 0.1μg/ml poly(I:C), p=0.0033). IFN-β production by TLR3 agonist also decreased in exacerbation but not statistically significant. Six older children showed decreased FOXP3 percentage in CD4+CD25^high and decreased suppression capability in exacerbation but restored in stabilization (82.8% vs. 90.0%, p=0.0061 and 60.9% vs. 81.7%, p=0.0071; respectively). In conclusion, normalizing imbalanced TLR signaling and enhancing Treg cell capability may guide possible therapeutic strategies for non-infectious asthma in exacerbation.