Antigen recognition in the immune system relies on four molecule types occupying two contrasting evolutionary/genetic strategies: Pattern Recognition Receptors and MHC molecules, each individually gene-encoded with limited diversity (low polymorphism for PRRs, high polymorphism between individuals for MHC but fixed number of loci), versus T-cell receptors and B-cell receptors/antibodies, which achieve enormous diversity (millions of specificities) through a unique somatic genetic recombination mechanism rather than one gene per receptor. This distinction underlies the difference between innate immune recognition (PRRs detecting conserved pathogen- and damage-associated molecular patterns) and adaptive immune recognition (TCRs and BCRs/antibodies achieving highly specific, individually generated antigen recognition), with the B-cell receptor uniquely existing in both membrane-bound and secreted (antibody) forms.
Antigen recognition in the immune system relies on four molecule types occupying two contrasting evolutionary/genetic strategies: Pattern Recognition Receptors and MHC molecules, each individually ge…