A variety of germline and somatic immune mechanisms have evolved in vertebrate and invertebrate species to detect a wide array of pathogenic invaders. The gut is a particularly significant site in terms of distinguishing pathogens from potentially beneficial microbes. Ciona intestinalis, a filter-feeding marine protochordate that is ancestral to the vertebrate form, possesses variable regioncontaining chitin-binding proteins (VCBPs), a family of innate immune receptors, which recognize bacteria through an immunoglobulin-type variable region. The manner in which VCBPs mediate immune recognition appears to be related to the development and bacterial colonization of the gut, and it is likely that these molecules are critical elements in achieving overall immune and physiological homeostasis.
Liberti, A., Leigh, B., De Santis, R., Pinto, M. R., Cannon, J. P., Dishaw, L. J., & Litman, G. W. (2015). An immune effector system in the protochordate gut sheds light on fundamental aspects of vertebrate immunity. In Results and Problems in Cell Differentiation (Vol. 57, pp. 159–173). Springer Verlag. https://doi.org/10.1007/978-3-319-20819-0_7