Specificity, promiscuity, and precursor frequency in immunoreceptors

•‘Universal’ TCR sequences such as NKT/MAIT recognize conserved pathogen features.•Role of ‘common’ near-germline TCR sequences in immune recognition.•Prevalent TCR sequences are efficiently produced by somatic gene recombination.

The immune system is comprised of various immune cell populations that utilize a spectrum of immunoreceptors characterized by different levels of specificity, diversity, and prevalence within a host and across a population. These range from the universal receptors employed by both innate cells and innate-like cells, such as NKT and MAIT cells, through to receptors expressed on T cells with sporadic incidence. Here we review recent advances in understanding the molecular mechanisms that drive the observed spectra of T cell receptors in vivo.