Discovery and verification of serum differential expression proteins for pulmonary tuberculosis

Pulmonary tuberculosis (PTB) is a chronic disease and has remained a severe threat to public health. Valuable biomarkers for improving the detection rate are crucial for controlling this disease. The purpose of this study was to discover potential biomarkers in sera from PTB patients compared with pneumonia patients and normal healthy controls. A total of 336 human serum specimens were enrolled in this study. Differentially expressed proteins were identified using iTRAQ method combining with MALDI-TOF-MS. Data was analyzed using relative bioinformatics methods. Potential biomarkers were further validated by IHC, ELISA and Western blot. As a result, 489 non-redundant proteins were identified in the sera, and 159 of which could be quantified by calculating their iTRAQ ratios. Compared to the controls, 26 differentially expressed proteins were recognized among PTB patients, including 16 overexpressed proteins and 10 downregulated proteins. Analysis of their functional interactions revealed that 12 proteins appeared in the center of the functional network. One of these key proteins, sex hormone binding globulin (SHBG), was found to be significantly elevated among PTB patients as compared with the controls examined by IHC, ELISA and Western blot. This result was consistent with the iTRAQ result. An independent blinded testing set to examine serum SHBG by ELISA achieved an accuracy of 78.74%, sensitivity of 75.6% and specificity of 91.5% in diagnosing PTB. In summary, iTRAQ in combination with MALDI-TOF-MS technology can efficiently screen differentially expressed proteins in sera from the PTB patients. SHBG is suggested to be a possible and novel serum biomarker for PTB.