The recombinant proteins were printed onto the PolymerSlide™ G slides (Captialbio, Beijing, China) using a SpotBot® 3 microarrayer (Arrayit corporation, click here Sunnyvale, CA). Five replicate spots per protein were printed, and mouse or human IgG were used as positive controls [4] and the E. coli cell lysate transformed with PET-32a plasmids was added as a negative control. The protein microarrays

were incubated in a humid chamber at 37°C overnight and stored at 4°C. For quality control, the proteins were incubated with Cy5labeled mouse antibody (IgG) to His tag fused with the proteins on the microarray. Only the proteins with a signal-to-background ratio of ≥3.0 were used for further analysis [33]. Serological analysis of the protein microarray

The protein microarrays were blocked in blocking buffer (8.1 mM Na2HPO4, 1.9 mM NaH2PO4, 154 mM NaCl, 1% [wt/vol] BSA, pH 7.4) for 1 h at 37°C. Human sera (1:100 dilutions) were neutralized overnight in PBS supplemented with the E. coli cell lysate at a final protein concentration of 5 mg/ml [21]. Fifty μl of the neutralized human sera were added to each well of the slides and incubated for 1 h at 37°C. The slides were washed 5 times with PBST (8.1 mM Na2HPO4, 1.9 mM NaH2PO4, 154 mM NaCl, 0.05% [vol/vol] Tween 20), and then incubated with Cy5-conjugated goat anti-mouse or human IgG (SBA, Gaithersburg, MD) diluted 1:500 in PBST for 1 h at 37°C. Following another 5 washes in PBST, the microarray was air dried and then scanned for fluorescent signals beta-catenin tumor at a wavelength of 635 nm using a GenePix Personal 4100A scanner (Molecular Devices, Sunnyvale, CA). The scanned images

were analyzed by GenePix pro 6.0 software (Molecular Devices, Sunnyvale, CA). The fluorescence intensity (FI) of each protein was calculated by averaging the FIs of 5 replicate spots that were background subtracted. The normalized data sets were then analysed by the kruskal-wallis H test using SPSS 16 software (IBM, Armonk, New York). Specificity analysis of the major seroreactive proteins The major seroreactive proteins identified in the above serological analysis were used to fabricate a protein microarray which was analyzed for its specificity with the sera from patients with Erastin concentration rickettsial spotted fever, Legionella pneumonia or streptococcal pneumonia. The sera of Q fever patients and healthy persons were used as positive and negative controls, respectively. The test and data analysis method were the same as those mentioned earlier. Acknowledgements This work was supported by grants (30901369 and 31170161) from National Natural Science Foundation of China, and a grant (2010CB530200/2010CB530205) from National Basic Research Program of China. Electronic supplementary material Additional file 1: Table S1 Primers designed for amplifying the genes encoding major seroreactive proteins.