Soluble Collectin-12 (CL-12) Is a Pattern Recognition Molecule Initiating Complement Activation via the Alternative Pathway

TY - JOUR

T1 - Soluble Collectin-12 (CL-12) Is a Pattern Recognition Molecule Initiating Complement Activation via the Alternative Pathway

AU - Ma, Ying Jie

AU - Hein, Estrid

AU - Munthe-Fog, Lea

AU - Skjødt, Mikkel-Ole

AU - Bayarri-Olmos, Rafael

AU - Romani, Luigina

AU - Garred, Peter

N1 - Copyright © 2015 by The American Association of Immunologists, Inc.

PY - 2015/10/1

Y1 - 2015/10/1

N2 - Soluble defense collagens including the collectins play important roles in innate immunity. Recently, a new member of the collectin family named collectin-12 (CL-12 or CL-P1) has been identified. CL-12 is highly expressed in umbilical cord vascular endothelial cells as a transmembrane receptor and may recognize certain bacteria and fungi, leading to opsonophagocytosis. However, based on its structural and functional similarities with soluble collectins, we hypothesized the existence of a fluid-phase analog of CL-12 released from cells, which may function as a soluble pattern-recognition molecule. Using recombinant CL-12 full length or CL-12 extracellular domain, we determined the occurrence of soluble CL-12 shed from in vitro cultured cells. Western blot showed that soluble recombinant CL-12 migrated with a band corresponding to ∼ 120 kDa under reducing conditions, whereas under nonreducing conditions it presented multimeric assembly forms. Immunoprecipitation and Western blot analysis of human umbilical cord plasma enabled identification of a natural soluble form of CL-12 having an electrophoretic mobility pattern close to that of shed soluble recombinant CL-12. Soluble CL-12 could recognize Aspergillus fumigatus partially through the carbohydrate-recognition domain in a Ca(2+)-independent manner. This led to activation of the alternative pathway of complement exclusively via association with properdin on A. fumigatus as validated by detection of C3b deposition and formation of the terminal complement complex. These results demonstrate the existence of CL-12 in a soluble form and indicate a novel mechanism by which the alternative pathway of complement may be triggered directly by a soluble pattern-recognition molecule.

AB - Soluble defense collagens including the collectins play important roles in innate immunity. Recently, a new member of the collectin family named collectin-12 (CL-12 or CL-P1) has been identified. CL-12 is highly expressed in umbilical cord vascular endothelial cells as a transmembrane receptor and may recognize certain bacteria and fungi, leading to opsonophagocytosis. However, based on its structural and functional similarities with soluble collectins, we hypothesized the existence of a fluid-phase analog of CL-12 released from cells, which may function as a soluble pattern-recognition molecule. Using recombinant CL-12 full length or CL-12 extracellular domain, we determined the occurrence of soluble CL-12 shed from in vitro cultured cells. Western blot showed that soluble recombinant CL-12 migrated with a band corresponding to ∼ 120 kDa under reducing conditions, whereas under nonreducing conditions it presented multimeric assembly forms. Immunoprecipitation and Western blot analysis of human umbilical cord plasma enabled identification of a natural soluble form of CL-12 having an electrophoretic mobility pattern close to that of shed soluble recombinant CL-12. Soluble CL-12 could recognize Aspergillus fumigatus partially through the carbohydrate-recognition domain in a Ca(2+)-independent manner. This led to activation of the alternative pathway of complement exclusively via association with properdin on A. fumigatus as validated by detection of C3b deposition and formation of the terminal complement complex. These results demonstrate the existence of CL-12 in a soluble form and indicate a novel mechanism by which the alternative pathway of complement may be triggered directly by a soluble pattern-recognition molecule.

KW - Aspergillus fumigatus

KW - Collectins

KW - Complement Activation

KW - Complement C3b

KW - Complement Pathway, Alternative

KW - Female

KW - Fetal Blood

KW - Human Umbilical Vein Endothelial Cells

KW - Humans

KW - Immunity, Innate

KW - Properdin

KW - Receptors, Scavenger

KW - Spores, Fungal

U2 - 10.4049/jimmunol.1500493

DO - 10.4049/jimmunol.1500493

M3 - Journal article

C2 - 26290605

SN - 0022-1767

VL - 195

SP - 3365

EP - 3373

JO - Journal of Immunology

JF - Journal of Immunology

IS - 7

ER -