The
activation-induced deaminase (AID)/APOBEC
cytidine deaminases participate in a diversity of biological processes from the regulation of
protein expression to embryonic development and host defenses. In its classical role, AID mutates germline-encoded sequences of B cell receptors, a key aspect of adaptive immunity, and APOBEC1, mutates
apoprotein B pre-mRNA, yielding two
isoforms important for cellular function and plasma lipid metabolism. Investigations over the last ten years have uncovered a role of the APOBEC superfamily in intrinsic immunity against viruses and innate immunity against
viral infection by deamination and mutation of viral genomes. Further, discovery in the area of human immunodeficiency virus (
HIV) infection revealed that the HIV viral infectivity factor
protein interacts with APOBEC3G, targeting it for proteosomal degradation, overriding its
antiviral function. More recently, our and others' work have uncovered that the AID and APOBEC
cytidine deaminase family members have an even more direct link between activity against
viral infection and induction and shaping of adaptive immunity than previously thought, including that of antigen processing for cytotoxic T lymphocyte activity and natural killer cell activation. Newly ascribed functions of these cytodine deaminases will be discussed, including their newly identified roles in adaptive immunity, epigenetic regulation, and cell differentiation. Herein this review we discuss AID and APOBEC cytodine deaminases as a link between innate and adaptive immunity uncovered by recent studies.