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Quorum sensing is the regulation of gene expression programmes in response to changes in population density. It is probably best recognized as a mechanism through which bacterial communities can synchronize behaviours, such as biofilm formation and bioluminescence. This Comment article highlights the emerging evidence suggesting that quorum sensing also contributes to the regulation of immune cell responses.
Transcriptional signatures of disease can be used for diagnosis or to gain insight into disease mechanisms. This Comment article discusses the different sets of criteria that should be considered for the optimal design of investigations addressing these two purposes, using examples from the study of tuberculosis.