Role of collectins in innate immunity

The collectins are a group of multimeric proteins in which the individual chains consist of a C-type lectin domain attached to a collagen domain via an alpha-coiled neck region. The chains are organized into a triple collagen helix and oligomerized through N-terminally located cysteines. The collectins have a dual function: these molecules can bind to sugar residues on the surface of a pathogen via the peripheral lectin domain; and subsequently interact through its collagen domain with phagocytes and/or the complement system to destroy the pathogen. The C-type lectin domains contain 110–130 amino-acid residues arranged in a conserved sequence pattern, which allows the domain to fold into a well-defined tertiary structure. Five collectins have been described. Lung surfactant proteins A and D (SP-A and SP-D) are mainly found in the surfactant coating the luminal surface ofthe pulmonary epithelial cells, but are also produced by cells lining the gastrointestinal tract. Mannan-binding lectin (MBL), conglutinin and collectin-43 (CL-43) are serum proteins produced by the liver. Conglutinin and CL-43 have so far only been found in Bovidae. The collectins are involved in innate, nonadaptive immune defense. Lack or low levels of the collectins may cause increase susceptibility to infections especially during the neonatal period between the maternally acquired immunity and a fully developed adaptive immunity also in the state of impaireil. immune functions. Therefore the collectins are the important molecules of the innate immunity. The present review deals with the structure and functional significance of various collectin molecules in innate immunity.