The innate immune response to DNA.

As a component of all living cells and microbes, it is not surprising that organisms have evolved mechanisms to detect foreign or aberrant DNA and trigger an innate immune response. TLR9 is an endosomal membrane bound receptor that is widely studied and the best understood DNA sensor. However, the existence of TLR9-independent DNA sensing pathways have been recognized for many years. Recently, novel cytosolic DNA sensors have been uncovered that include ZBP1 or DNA-dependent activator of interferon-regulatory factors (DAI) and a DNA sensing inflammasome consisting of the HIN200 protein, absent in melanoma 2 (AIM2). In combination with TLR9, these receptors provide a diverse repertoire of mechanisms to alert the cell to microbial DNA and possibly aberrant host DNA leading to the activation of the innate immune system.