Capture of heat-killed Mycobacterium bovis bacillus Calmette-Guerin by intelectin-1 deposited on cell surfaces

Abstract

Intelectin is an extracellular animal lectin found in chordata. Although human and mouse intelectin-1 recognize galactofuranosyl residues included in cell walls of various microorganisms, the physiological function of mammalian intelectin had been unclear. In this study, we found that human intelectin-1 was a serum protein and bound to Mycobacterium bovis bacillus Calmette-Guérin (BCG). Human intelectin-1-binding to BCG was inhibited by Ca(2+)-depletion, galactofuranosyl disaccharide, ribose, or xylose, and was dependent on the trimeric structure of human intelectin-1. Although monomeric, mouse intelectin-1 bound to BCG, with its C-terminal region contributing to efficient binding. Human intelectin-1-transfected cells not only secreted intelectin-1 into culture supernatant but also expressed intelectin-1 on the cell surface. The cell surface intelectin-1 was not a glycosylphosphatidylinositol-anchored membrane protein. Intelectin-1-transfected cells captured BCG more than untransfected cells, and the BCG adherence was inhibited by an inhibitory saccharide of intelectin-1. Intelectin-1-preincubated cells took up BCG more than untreated cells, but the adhesion of intelectin-1-bound BCG was the same as that of untreated BCG. Mouse macrophages phagocytosed BCG more efficiently in medium containing mouse intelectin-1 than in control medium. These results indicate that intelectin is a host defense lectin that assists phagocytic clearance of microorganisms.

Autophagy Protects against Colitis by the Maintenance of Normal Gut Microflora and Secretion of Mucus

“…Angiogenin-4 (encoded by Ang4) has bactericidal activity against several Gram-positive enteric microbes, such as Enterococcus faecalis (38), although E. faecalis was not detectable in our mice. 3 Intelectin-1 (encoded by Itln1) is a host defense lectin that assists phagocytic clearance of microorganisms (43) and is encoded in one of the IBD susceptibility loci (62). This is consistent with our finding that Itln1 was decreased in the colon of Atg7 cKO mice.…”

“…Next, we performed gene ontology analysis of differentially expressed genes induced by bacterial infection (GO:0042742) or nematode infection (GO:0009624) with a cutoff value of 100. As a result, we found that Itln1 encoding intelectin-1, which is known to be involved in bacterial clearance (43), and Itln2 encoding its homologue intelectin-2 (44) fulfilled these criteria.…”

Soluble Human Intestinal Lactoferrin Receptor: Ca²⁺-Dependent Binding to Sepharose-Based Matrices

“…6) Additionally, hITLN-1 binds to Mycobacterium bovis bacillus Calmette-Guérin (BCG) and assists in the phagocytic removal of this microorganism. 3) In the present study, we found that recombinant shLFR (hITLN-1) binds tightly to Sepharose (4 Fast Flow [FF], 4B and 6B)-based matrices in a Ca 2+ -dependent manner. This binding property is most likely related to the ability of shLFR, as a host defense lectin, to recognize sepharose (agarobiose)-like, bacteria-specific components that are present on the surface of invading pathogenic microorganisms.…”

“…1) A soluble form of hLFR (shLFR) is identical to human intelectin-1 (hITLN-1), 2) a galactofuranose-binding protein that plays a role in host defense as lectins to assist in the phagocytic removal of microorganisms. 3) hLFR is expressed as a glycosylphosphatidylinositol (GPI)-anchored protein on human intestinal epithelial cells, Caco-2, 4) while hITLN-1 is expressed as a secretory protein (not as a GPI-anchored protein) in rabbit kidney epithelial cell (RK13) transfectants, despite being present on the cell surface.…”

“…3) Although cell-specific expression of hLFR has been reported, [3][4][5] a major form of hLFR (hITLN-1) was expressed as a secretory protein in insect 4) and RK13 6) transfectants. Recombinant shLFR (hITLN-1) is a disulfidelinked, 120-kDa, homotrimeric polypeptide under nonreducing conditions, but is a 40-kDa, monomeric polypeptide under reducing conditions.…”