The iTRAQ quantitation results and gene ontology analyses show that the number of differentially expressed apoptosis-related proteins increases in macrophages as the infection proceeds (Fig. 2, Fig. 3A , Fig. S2 ). Our proteomics data showed, for example, that the amount of Bax decreases in the cytoplasmic fraction and increases in the mitochondrial fraction, and the amount of cytochrome c decreases in the mitochondrial fraction and increases in the cytoplasmic fraction upon infection (Fig. 3A) . These data together with Western blot analysis of cytochrome c (Fig. S1 ) are well in accordance with classical signs of mitochondrial apoptosis: translocation of Bax onto the mitochondria and leakage of cytochrome c into the cytoplasm.