ReceptorsVLRA

ReceptorsVLRA, commonly abbreviated VLRA, are a family of variable lymphocyte receptors found in jawless vertebrates such as lampreys. They are part of the three-family system (VLRA, VLRB, VLRC) that constitutes the adaptive immune repertoire of these species, a mechanism distinct from the immunoglobulin- and T cell receptor-based system of jawed vertebrates.

VLRA receptors are single-pass, type I membrane proteins built from leucine-rich repeat modules. The diversity of VLRA arises not from V(D)J-like recombination but from somatic assembly of donor leucine-rich repeat cassettes into the VLR gene locus within developing lymphocytes. This modular, cassette-based assembly creates a highly diverse set of antigen receptors capable of recognizing a wide array of pathogens.

Expression of VLRA marks a T-like lineage of lamprey lymphocytes. In addition to the VLRA (T-like) lineage, lampreys also express VLRB (B-like) receptors that are secreted as soluble humoral receptors, and VLRC (cytotoxic/regulatory-like) receptors associated with another lineage. Each mature lymphocyte typically expresses a single VLRA allele on the cell surface, reflecting clonal diversity generated by somatic assembly.

Functionally, VLRA-expressing cells participate in cellular immune responses, activating upon antigen recognition and contributing to targeted defense. The VLRA/VLRB/VLRC system provides complementary arms of adaptive immunity in lampreys, enabling clonal-like specificity and robust pathogen recognition without conventional antibodies or T cell receptors.