Collectins: sentinels of innate immunity

Abstract

Collectins, present in plasma and on mucosal surfaces, are humoral molecules of the innate immune system. They were discovered a hundred years ago in 1906 as the first association of an animal lectin with the immune system. They are a family of calcium-dependent lectins that recognize pathogen-associated molecular patterns. They share a similar modular domain architecture consisting of four regions; a cysteine-rich N-terminal domain, a collagen-like region, an alpha-helical neck domain and a C-terminal carbohydrate recognition domain. There have been eight collectins members defined so far, of which, MBL, SP-A and SP-D are the most characterized. Collectins represent the first line of host defense. Upon recognition of the infectious agents, collectins put into action effector mechanisms like direct opsonization, neutralization, agglutination, complement activation and phagocytosis to curb the microbial growth. In addition, they also modulate inflammatory and allergic responses and apoptotic cell clearance. These functions limit infection and subsequently modulate the adaptive immune responses. The role of collectins, their structure, function, characteristics and clinical significance are reviewed in this article.

The genome of the choanoflagellate Monosiga brevicollis and the origin of metazoans

“…Gene structure and intron evolution The ,41.6 megabase (Mb) M. brevicollis genome contains approximately 9,200 genes (Supplementary Notes 1 and 2) and is comparable in size to the genomes of filamentous fungi (,30-40 Mb) and other free-living unicellular eukaryotes (for example, small diatoms at , [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] and ichthyosporeans at ,20-25 Mb 21 ). Metazoan genomes are typically larger, with few exceptions 22 .…”

“…At least 23 M. brevicollis genes encode one or more cadherin domains, homologues of which are required for cell sorting and adhesion during metazoan embryogenesis 24 , and 12 genes encode C-type lectins, 2 of which are transmembrane proteins. Whereas soluble C-type lectins have functions ranging from pathogen recognition to ECM organization, transmembrane C-type lectins mediate specific adhesive activities such as contact between leukocytes and vascular endothelial cells, cell recognition, and molecular uptake by endocytosis [25][26][27] . The genome of M. brevicollis also contains integrin-a and immunoglobulin domains-cell adhesion domains formerly thought to be restricted to metazoans.…”

Surfactant Protein A (SP-A)-mediated Clearance of Staphylococcus aureus Involves Binding of SP-A to the Staphylococcal Adhesin Eap and the Macrophage Receptors SP-A Receptor 210 and Scavenger Receptor Class A

“…Surfactant protein A (SP-A) 3 is a crucial component of the pulmonary innate immune system in the alveolar spaces (5,6). SP-A is the major protein constituent of pulmonary surfactant; it is involved in organization of large aggregate surfactant phospholipids lining the alveolar surface and acts as an opsonin for pathogens (7).…”

Beneficial Effects of Grape Resveratrol on Serum Adiponectin and Inflammation: Clinical Trial in Patients with Stable Coronary Artery Disease

“…Epidemiological studies confirmed the low circulatory levels of adiponectin in CAD [23,24]. Adiponectin participates in the in vivo clearance of apoptotic cellular bodies and blebs of dying cells by binding them, leading to phagocytosis by monocyte derived macrophages, thereby minimizing tissue injury and inflammation [25,26]. Adiponectin dependent suppression of inflammatory cytokines is well established in in vitro and in vivo studies [2,20,27].…”