In conclusion, blood transcript profi ling has earned its place in the molecular and cellular profi ling armamentarium used to study the human immune system. Changes in transcript abundance recapitulate the infl uence of genetic, epigenetic, cellular and environ mental factors. Initially considered to belong to the 'cutting edge' , this approach has become both robust and practical. As discussed in this review, it has become a mainstay for the study of immune function in patients with a wide range of diseases. Furthermore, recent studies have demonstrated the utility of blood transcriptome profi ling for monitoring immune responses to drugs or vaccines [35, 142, 143] . Th us, blood transcript profi ling is developing Relative changes in transcript abundance in the blood of patients with S. aureus infection compared to that of healthy controls are recorded for a set of 28 transcriptional modules. Colored spots represent relative increase (red) or decrease (blue) in transcript abundance (P < 0.05, Mann Whitney) within a module. The legend shows functional interpretation for this set of modules. Fingerprints have been generated for two independent cohorts of subjects (divided into a training set used in the discovery phase, n = 30, and an independent test set used in the validation phase, n = 32).