AIMS: We sought to determine whether myocardial expression of Toll-like receptor 4 (TLR4) may predict the response to immunosuppression.
METHODS AND RESULTS: Endomyocardial biopsies from 237 patients with virus-negative inflammatory cardiomyopathy treated with immunosuppression were retrospectively examined for the expression of TLR4, differentiating those patients responding to immunosuppression (n = 193) from non-responder patients (n = 44). A semiquantitative evaluation of the immunoreactivity (grading from 0 to 4) for TLR4 and human leucocyte antigen (HLA)-DR was performed together with real-time PCR and western blot for TLR4. Cardiomyocyte apoptosis and necrosis was evaluated by in situ ligation with hairpin probes. A focal intense positive cytoplasmic immunostaining for TLR4 was observed in cardiomyocytes of all responders (P < 0.001 vs. non-responders). A grading 2 or above (2+) at baseline showed a sensitivity of 100% and 90.9% specificity with a positive predictive value of 98% as a predictor of an immunosuppression-positive response. Real-time PCR and western blot analysis for TLR4 were 4.3-fold and 4.6-fold higher, respectively, in responders vs. non-responders. Correlation between TLR4 grading and TLR4 mRNA molecular and protein expression was highly significant. HLA-DR did not discriminate between the two groups. Cardiomyocyte death by apoptosis was 3.7-fold higher in responders vs. non-responders and significantly correlated with TLR4 expression, while necrosis was comparable. Intensity of baseline TLR4 expression correlated with the variation in ejection fraction after 6 months of immunosuppression.
CONCLUSION: TLR4 is highly expressed in human myocarditis responding to immunosuppression. It can be considered as a new sensitive marker in patient selection predicting a good response to immunosuppressive therapy.