Epigenetics and innate immunity: the 'unTolld' story

Toll-like receptors (TLRs) are a family of 13 receptors known as pattern-recognition receptors (PRRs) and have a key role in the innate immune response. The TLRs are activated by pathogen-associated molecular patterns (PAMPs) that are structurally conserved molecules present on the surfaces of bacteria and viruses. The activation of these TLRs by pathogens results in the downstream activation of genes involved in the production of proinflammatory factors. There is a lack of understanding on the mechanisms by which TLR gene expression is regulated. Epigenetics could be one such mechanism, which is concerned with changes in gene expression/products that arise without a change in the nucleotide sequence. These changes are brought about by two main mechanisms, DNA methylation and histone modifications. This review seeks to examine the current knowledge regarding the epigenetic regulation of this family of receptors and their signalling pathways.