Collectins are a family of C-type lectins that have collagen-like sequences and carbohydrate recognition domains (CRD). They are involved in host defense through their ability to bind to carbohydrate antigens of microorganisms. The scavenger receptors type A and MARCO are classical type scavenger receptors that have internal collagen-like domains. Here we describe a new scavenger receptor that is a membrane-type collectin from placenta (collectin placenta 1 (CL-P1)), which has a typical collectin collagen-like domain and a CRD. The cDNA has an insert of about 2.2 kilobases coding for a protein containing 742 amino acid residues. The deduced amino acid sequence shows that CL-P1 is a type II membrane protein, has a coiled-coil region, a collagen-like domain, and a CRD. It resembles type A scavenger receptors because the scavenger receptor cysteine-rich domain is replaced by a CRD. Northern analyses, reverse transcription-polymerase chain reaction, and immunohistochemistry show that CL-P1 is expressed in vascular endothelial cells but not in macrophages. By immunoblotting and flow cytometry CL-P1 appears to be a membrane glycoprotein of about 140 kDa in human umbilical vein or arterial endothelial cells, placental membrane extracts, and CL-P1 transfected Chinese hamster ovary cells. We found that CL-P1 can bind and phagocytose not only bacteria (Escherichia coli and Staphylococcus aureus) but also yeast (Saccharomyces cerevisiae). Furthermore, it reacts with oxidized low density lipoprotein (OxLDL) but not with acetylated LDL (AcLDL). These binding activities are inhibited by polyanionic ligands (polyinosinic acid, polyguanylic acid, dextran sulfate) and OxLDL but not by polycationic ligands (polyadenylic acid or polycytidylic acid), LDL, or AcLDL. These results indicate that CL-P1 might play important roles in host defenses that are different from those of soluble collectins in innate immunity.

Collectins are a family of C‐type lectins with two characteristic structures, collagen like domains and carbohydrate recognition domains. They recognize carbohydrate antigens on microorganisms and act as host‐defense. Here we report the cloning and characterization of a novel collectin CL‐K1. RT‐PCR analyses showed CL‐K1 mRNA is present in all organs. The deduced amino acid sequence and the data from immunostaining of CL‐K1 cDNA expressing CHO cells revealed that CL‐K1 is expressed as a secreted protein. CL‐K1 is found in blood by immunoblotting and partial amino acid analyses. CL‐K1 showed Ca2+‐dependent sugar binding activity of fucose and weakly mannose but not N‐acetyl‐galactosamine, N‐acetyl‐glucosamine, or maltose, though mannose‐binding lectin (MBL) containing similar amino acid motif. CL‐K1 can recognize specially several bacterial saccharides due to specific sugar‐binding character. Elucidation of the role of two ancestor collectins of CL‐K1 and CL‐L1 could lead to see the biological function of collectin family.

Collectins are a C-lectin family with collagen-like sequences and carbohydrate recognition domains. These proteins can bind to carbohydrate antigens of microorganisms and inhibit their infection by direct neutralization and agglutination, the activation of complement through the lectin pathway, and opsonization by collectin receptors. Here we report the cloning of a cDNA encoding human collectin from liver (CL-L1 (collectin liver 1)) that has typical collectin structural characteristics, consisting of an N-terminal cysteine-rich domain, a collagen-like domain, a neck domain, and a carbohydrate recognition domain. The cDNA has an insert of 831 base pairs coding for a protein of 277 amino acid residues. The deduced amino acid sequence shows that this collectin has a unique repeat of four lysine residues in its C-terminal area. Northern blot, Western blot, and reverse transcription-polymerase chain reaction analyses showed that CL-L1 is present mainly in liver as a cytosolic protein and at low levels in placenta. More sensitive analyses by reverse transcription-polymerase chain reactions showed that most tissues (except skeletal muscle) have CL-L1 mRNA. Zoo-blot analysis indicated that CL-L1 is limited to mammals and birds. A chromosomal localization study indicated that the CL-L1 gene localizes to chromosome 8q23-q24.1, different from chromosome 10 of other human collectin genes. Expression studies of fusion proteins lacking the collagen and N-terminal domains produced in Escherichia coli affirmed that CL-L1 binds mannose weakly. CL-L1 and recombinant CL-L1 fusion proteins do not bind to mannan columns. Analysis of the phylogenetic tree of CL-L1 and other collectins indicated that CL-L1 belongs to a fourth subfamily of collectins following the mannan-binding protein, surfactant protein A, and surfactant protein D subfamilies including bovine conglutinin and collectin-43 (CL-43). These findings indicate that CL-L1 may be involved in different biological functions.

We report herein the detection of intracellular bacteria in phagocyte-smears obtained from septicemia-suspected blood samples by in situ hybridization . This was obtained by using nicktranslated biotin-11-dUTP-labeled DNA probes and streptavidin-alkaline phosphatase conjugates for visualization of the hybridized signals. The probes were made from random genomic DNA clones of bacteria which are frequently the causative agents of bacteremia, such as Staphylococcus spp ., Pseudomonas aeruginosa, Enterococcus faecalis, Escherichia coli, Klebsiella spp . and Enterobacter spp. When our in situ hybridization method was compared with conventional culture protocols for the ability to detect bacteria from the blood of patients suspected of having septicemia , 30 positive results were obtained in 50 specimens by in situ hybridization methods. In contrast , only 7 positive results were obtained by blood cultures. Thus, even if bacteria cannot be detected by conventional blood cultures and histology, our in situ hybridization method allows for direct observation of bacterial foci in circulating phagocytes and identification of the bacteria . Our investigations suggest that in septicemia, circulating polymorphonuclear neutrophils carry some surviving bacteria as well as metabolized bacterial DNA and RNA for a considerable period of time. Thus , our in situ hybridization method using the phagocyte-smears have diagnostic value for detecting most bacteria which cause septicemia.

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