Development of a Quantitative Assay for the Characterization of Human Collectin-11 (CL-11, CL-K1)

Collectin-11 (CL-11) is a pattern recognition molecule of the lectin pathway of complement with diverse functions spanning from host defense to embryonic development. CL-11 is found in the circulation in heterocomplexes with the homologous collectin-10 (CL-10). Abnormal CL-11 plasma levels are associated with the presence of disseminated intravascular coagulation, urinary schistosomiasis, and congenital disorders. Although there has been a marked development in the characterization of CL-11 there is still a scarcity of clinical tools for its analysis. Thus, we generated monoclonal antibodies and developed a quantitative ELISA to measure CL-11 in the circulation. The antibodies were screened against recombinant CL-11 and validated by ELISA and immunoprecipitation of serum and plasma. The best candidates were pairwise compared to develop a quantitative ELISA. The assay was validated regarding its sensitivity, reproducibility, and dilution linearity, demonstrating a satisfactory variability over a working range of 0.29–18.75 ng/ml. The mean plasma concentration of CL-11 in healthy controls was determined to be 289.4 ng/ml (range 143.2–459.4 ng/ml), highly correlated to the levels of CL/10/11 complexes (r = 0.729). Plasma CL-11 and CL-10/11 co-migrated in size exclusion chromatography as two major complexes of ~400 and >600 kDa. Furthermore, we observed a significant decrease at admission in CL-11 plasma levels in patients admitted to intensive care with systemic inflammatory response syndrome. By using the in-house antibodies and recombinant CL-11, we found that CL-11 can bind to zymosan independently of calcium by a separate site from the carbohydrate-binding region. Finally, we showed that CL-11/MASP-2 complexes trigger C4b deposition on zymosan. In conclusion, we have developed a specific and sensitive ELISA to investigate the ever-expanding roles of CL-11 in health and disease and shown a novel interaction between CL-11 and zymosan.

An enzyme-linked immunosorbent assay (ELISA) for quantification of human collectin 11 (CL-11, CL-K1)

Collectin 11 (CL-11), also referred to as collectin kidney 1 (CL-K1), is a pattern recognition molecule that belongs to the collectin group of proteins involved in innate immunity. It interacts with glycoconjugates on pathogen surfaces and has been found in complex with mannose-binding lectin-associated serine protease 1 (MASP-1) and/or MASP-3 in circulation. Mutation in the CL-11 gene was recently associated with the developmental syndrome 3MC. In the present study, we established and thoroughly validated a sandwich enzyme-linked immunosorbent assay (ELISA) based on two different monoclonal antibodies. The assay is highly sensitive, specific and shows excellent quantitative characteristics such as reproducibility, dilution linearity and recovery (97.7-104%). The working range is 0.15-34 ng/ml. The CL-11 concentration in two CL-11-deficient individuals affected by the 3MC syndrome was determined to be below 2.1 ng/ml. We measured the mean serum CL-11 concentration to 284 ng/ml in 100 Danish blood donors, with a 95% confidence interval of 269-299 ng/ml. There was no significant difference in the CL-11 concentration measured in matched serum and plasma samples. Storage of samples and repeated freezing and thawing to a certain extent did not influence the ELISA. This ELISA offers a convenient and reliable method for studying CL-11 levels in relation to a variety of human diseases and syndromes.

Serum concentration and interaction properties of MBL/ficolin associated protein-1

Recently, a novel protein named MBL/ficolin associated protein-1 (MAP-1) derived from the MASP1 gene through differential splicing was identified. In the present study, we established biochemical characteristics, determined the serum level and assessed the interactions between the lectin complement pathway (LCP) recognition molecules and MAP-1. We expressed recombinant MAP-1 in CHO DG44 cells, developed a quantitative ELISA assay based on a MAP-1 specific monoclonal capture antibody and measured the serum levels in 100 Danish blood donors. In addition we assessed the association properties between MAP-1 and Ficolin-2, -3 and MBL in serum using ELISA and density gradient ultra centrifugation. When recombinant MAP-1 was subjected to N-glycosidase F treatment the molecular mass decreased from ∼45 kDa to ∼40 kDa equivalent with the calculated molecular mass from the deduced amino acid sequence without the signal peptide. We found that serum MAP-1 was very stable when subjected to repeated freeze and thaw cycles. The mean serum concentration of MAP-1 was found to be 240 ng/ml (range: 115-466 ng/ml). MAP-1 was predominantly found in complex with Ficolin-3 and to a lesser degree with Ficolin-2 and MBL and by use of density gradient ultra centrifugation we could show that the major part of serum MAP-1 circulates in complex with the LCP molecules. In conclusion, these results show that MAP-1 is a highly stable glycosylated human serum protein found in complex with Ficolin-3, Ficolin-2 and MBL.

Novel assays to assess the functional capacity of the classical, the alternative and the lectin pathways of the complement system

Deficiencies in many of the complement proteins and their regulatory molecules have been described and a variety of diseases, such as recurrent infections, systemic lupus erythematosus (SLE) and renal diseases, may be linked to deficiency in the complement system. Screening for complement defects is therefore of great importance. In this study, we present novel improved enzyme-linked immunosorbent assays for the functional assessment of the three individual pathways of the complement system. The method is applicable at high serum concentrations and we demonstrate that it minimizes both false negative as well as false positive results. In particular, for the functional mannose-binding lectin activity it represents an improvement on the existing assays. In this respect, the present assays represent novel improved diagnostic protocols for patients with suspected immunodeficiencies related to the complement system.

Evolutionary conservation of mannan-binding lectin (MBL) in bony fish: identification, characterization and expression analysis of three bona fide collectin homologues of MBL in the rainbow trout (Onchorhynchus mykiss)

The complement system of fish is generally as complex as in mammals, and in addition Teleost fish often possess several genes encoding different subtypes of a given complement component, such as C3-1, C3-3 and C3-4. Initiators of both the classical (C1) and alternative pathway (factor B) have been characterized in the rainbow trout but so far no molecules of the lectin pathway have been identified. Based on the generally accepted idea of complement evolution, which predicts that the alternative pathway predates the two other pathways, and that the lectin pathway developed before the classical, we set out to characterize members of the lectin pathway in fish. We identified and characterized three homologues of mannan-binding lectin (MBL) with a bona fide collectin structure. By means of RT-PCR and immunohistochemistry using monoclonal antibodies we found that they were synthesized in the spleen, the anterior intestine and the liver. In the liver, we saw co-expression with mannan-binding lectin associated serine protease (MASP). The MBL homologues 2 and 3 (MBL-H2,3) were also found in the vascular system of the rainbow trout. By means of gel size exclusion chromatography of serum we found that MBL-H2,3 oligomerized heterogeneously from monomers to tetramers of a trimeric collagenous subunit. Sequence comparison and phylogenetic studies showed that the homologues were more related with MBL than any other collectins, and that two previously characterized trout proteins, designated MBL1 and MBL2, should be reconsidered as MBL candidates.

Generation of a C3c specific monoclonal antibody and assessment of C3c as a putative inflammatory marker derived from complement factor C3

There is a general need for markers of systemic inflammation in acute or chronic diseases, where complement activation is involved. Available methods to monitor complement activation are elaborate and of low sensitivity; they include haemolytic assays (CH50), quantification of fluid phase terminal complex (C5b-C9) and quantification of complement split products by precipitation-in-gel techniques (e.g. C3d). We have developed a mouse monoclonal antibody (mAb) that is able to detect fluid phase C3c without interference from other products generated from the complement component C3. The C3c specific mAb was tested in different ELISA combinations with various types of in vitro activated sera and with plasma or serum samples from factor I deficient patients. The specificity of the mAb was evaluated in immunoprecipitation techniques and by analysis of eluted fragments of C3 after immunoaffinity chromatography. The C3c mAb was confirmed to be C3c specific, as it showed no cross-reactivity with native (un-cleaved) C3, with C3b, iC3b, or with C3d. Also, no significant reaction was observed with C3 fragments in factor I deficient sera or plasma. This antibody forms the basis for the generation of a robust ELISA that allows for a quick and reliable evaluation of complement activation and consumption as a marker for inflammatory processes. We established the C3c plasma range in 100 healthy Danish blood donors with a mean of 3.47 μg/ml and a range of 2.12-4.92 μg/ml. We believe that such an antibody might be of potential value in the assessment of in vivo complement activity during the inflammatory processes.

A novel mannose-binding lectin/ficolin-associated protein is highly expressed in heart and skeletal muscle tissues and inhibits complement activation

The human lectin complement pathway involves circulating complexes consisting of mannose-binding lectin (MBL) or three ficolins (ficolin-1, -2, and -3) in association with three MBL/ficolin-associated serine proteases (MASP) (MASP-1, -2, and -3) and a nonenzymatic sMAP. MASP-1 and MASP-3 (MASP1 isoforms 1 and 2, respectively) are splice variants of the MASP1 gene, whereas MASP-2 and sMAP are splice variants of the MASP2 gene. We have identified a novel serum protein of 45 kDa that is associated with MBL and the ficolins. This protein is named MBL/ficolin-associated protein 1 (MAP-1 corresponding to MASP1 isoform 3). The transcript generating MAP-1 (MASP1_v3) contains exons 1-8 and a novel exon encoding an in-frame stop codon. The corresponding protein lacks the serine protease domains but contains most of the common heavy chain of MASP-1 and MASP-3. Additionally MAP-1 contains 17 unique C-terminal amino acids. By use of quantitative PCR and MAP-1-specific immunohistochemistry, we found that MAP-1 is highly expressed in myocardial and skeletal muscle tissues as well as in liver hepatocytes with a different expression profile than that observed for MASP-1 and MASP-3. MAP-1 co-precipitated from human serum with MBL, ficolin-2, and ficolin-3, and recombinant MAP-1 was able to inhibit complement C4 deposition via both the ficolin-3 and MBL pathway. In conclusion we have identified a novel 45-kDa serum protein derived from the MASP1 gene, which is highly expressed in striated muscle tissues. It is found in complex with MBL and ficolins and may function as a potent inhibitor of the complement system in vivo.

Two mannose-binding lectin homologues and an MBL-associated serine protease are expressed in the gut epithelia of the urochordate species Ciona intestinalis

The lectin complement pathway has important functions in vertebrate host defence and accumulating evidence of primordial complement components trace its emergence to invertebrate phyla. We introduce two putative mannose-binding lectin homologues (CioMBLs) from the urochordate species Ciona intestinalis. The CioMBLs display similarities with vertebrate MBLs and comprise a collagen-like region, alpha-helical coiled-coils and a carbohydrate recognition domain (CRD) with conserved residues involved in calcium and carbohydrate binding. Structural analysis revealed an oligomerization through interchain disulphide bridges between N-terminal cysteine residues and cysteines located between the neck region and the CRD. RT-PCR showed a tissue specific expression of CioMBL in the gut and by immunohistochemistry analysis we also demonstrated that CioMBL co-localize with an MBL-associated serine protease in the epithelia cells lining the stomach and intestine. In conclusion we present two urochordate MBLs and identify an associated serine protease, which support the concept of an evolutionary ancient origin of the lectin complement pathway.

Novel characterisation of the gene encoding conglutinin reveals that previously characterised promoter corresponds to the CL-43 promoter

Conglutinin, a collectin found in bovine serum, is an opsonin that binds to glycoconjugates on the surface of microorganisms or on deposited iC3b, and acts in concert with phagocytes to establish a first-line of immune defense. We have isolated a genomic conglutinin phage clone and found that the 5'-flanking region shows 95.8% identity with the sequence previously published, which on the other hand shows 99.7% identity with the CL-43 promoter. We conclude that the previously published promoter corresponds to the CL-43 promoter and that the functional studies performed on it apply to transcription of CL-43. Comparison of potential cis-regulatory elements in relation to the functional studies indicates that the two genes are regulated by different mechanisms.

Cloning of a novel scavenger receptor cysteine-rich type I transmembrane molecule (M160) expressed by human macrophages

We report the cloning of a novel human type I cell surface Ag mainly expressed by macrophages. The primary structure was established by molecular cloning, which yielded a 4579-bp cDNA sequence encoding a polypeptide chain of 1453 amino acid residues with 16 potential N:-glycosylation sites. We designated this molecule M160. The domain organization features 12 scavenger receptor cysteine-rich domains followed by a transmembrane region and a cytoplasmic domain that occurs in two forms, a predominant form (M160-alpha) of 71 residues and an alternatively spliced form (M160-ss) of 39 residues. M160-alpha contains three possible phosphorylation sites, which are lost in the alternatively spliced form. RT-PCR analyses showed M160 to be expressed by alveolar macrophages and by the monocyte cell lines HL60, U937, and THP1, but not by Jurkat or Raji cells. Stimulation of U937 cells with phorbol ester resulted in an increased expression of M160 from day 5 onward. RT-PCR analysis of 19 different human tissues showed signals for M160-alpha of varying intensity in all tissues, whereas M160-ss was confined to the spleen. We conclude that M160 is a new member of the scavenger receptor cysteine-rich superfamily expressed by the monocyte/macrophage cell lineage.

Localization of lung surfactant protein D on mucosal surfaces in human tissues

Lung surfactant protein-D (SP-D), a collectin mainly produced by alveolar type II cells, initiates the effector mechanisms of innate immunity on binding to microbial carbohydrates. A panel of mRNAs from human tissues was screened for SP-D mRNA by RT-PCR. The lung was the main site of synthesis, but transcripts were readily amplified from trachea, brain, testis, salivary gland, heart, prostate gland, kidney, and pancreas. Minor sites of synthesis were uterus, small intestine, placenta, mammary gland, and stomach. The sequence of SP-D derived from parotid gland mRNA was identical with that of pulmonary SP-D. mAbs were raised against SP-D, and one was used to locate SP-D in cells and tissues by immunohistochemistry. SP-D immunoreactivity was found in alveolar type II cells, Clara cells, on and within alveolar macrophages, in epithelial cells of large and small ducts of the parotid gland, sweat glands, and lachrymal glands, in epithelial cells of the gall bladder and intrahepatic bile ducts, and in exocrine pancreatic ducts. SP-D was also present in epithelial cells of the skin, esophagus, small intestine, and urinary tract, as well as in the collecting ducts of the kidney. SP-D is generally present on mucosal surfaces and not restricted to a subset of cells in the lung. The localization and functions of SP-D indicate that this collectin is the counterpart in the innate immune system of IgA in the adaptive immune system.

The structural basis for complement receptor type 2 (CR2, CD21)-mediated alternative pathway activation of complement: studies with CR2 deletion mutants and vaccinia virus complement-control protein-CR2 chimeras

The role of complement receptor 2 (CR2) short consensus repeats (SCR) in binding of hydrolyzed C3 (iC3) to form an alternative pathway (AP) convertase, and promoting C3 fragment deposition following AP activation, was examined. We used (1) K562 cells transfected with CR2 constructs, where the C3d-binding site of CR2 (SCR1+2) was replaced with the four-SCR vaccinia virus complement control protein (VCP), or truncation mutants thereof, and (2) COS cells transfected with wild-type (wt) CR2, or deletion mutants thereof. AP activation required iC3 binding in both systems. Thus, the VCP-CR2 chimera had an iC3 binding efficiency of 11.4 %, compared to wtCR2, and a relative AP activity of 5.5 %, the truncation mutants being inactive. Of the CR2 mutants, only EK (DeltaSCR10 - 11) had AP activity similar to wtCR2. NN (DeltaSCR6 - 8) and NOP (DeltaSCR6-mid14) had reduced AP activity, but near normal iC3 binding. XB (DeltaSCR3 - 6) and PP (DeltaSCR3-mid14) were inactive in both assays. We conclude that, whilst iC3 binding to CR2 via SCR1 - 4 is essential for AP activation, the efficiency of C3 deposition also depends on the midportion of CR2.

Cloning of gp-340, a putative opsonin receptor for lung surfactant protein D

Surfactant protein D (SP-D) is an oligomeric C type lectin that promotes phagocytosis by binding to microbial surface carbohydrates. A 340-kDa glycoprotein (gp-340) has been shown to bind SP-D in the presence of calcium but does so independently of carbohydrate recognition. This protein exists both in a soluble form and in association with the membranes of alveolar macrophages. The primary structure of gp-340 has been established by molecular cloning, which yielded a 7,686-bp cDNA sequence encoding a polypeptide chain of 2, 413 amino acids. The domain organization features 13 scavenger receptor cysteine-rich (SRCR) domains, each separated by an SRCR-interspersed domain, except for SRCRs 4 and 5, which are contiguous. The 13 SRCR domains are followed by two C1r/C1s Uegf Bmp1 domains separated by a 14th SRCR domain and a zona pellucida domain. gp-340 seems to be an alternative spliced form of DMBT1. Reverse transcription-PCR analysis showed that the main sites of synthesis of gp-340 are lung, trachea, salivary gland, small intestine, and stomach. Immunohistochemistry revealed strong staining for gp-340 in alveolar and other tissue macrophages. Immunostaining of the macrophage membrane was either uniform or focal in a way that suggested capping, whereas other macrophages showed strong intracellular staining within the phagosome/phagolysosome compartments. In some macrophages, SP-D and gp-340 were located in the same cellular compartment. Immunoreactive gp-340 was also found in epithelial cells of the small intestine and in the ducts of salivary glands. The distribution of gp-340 in macrophages is compatible with a role as an opsonin receptor for SP-D.

Clinical significance of cyclin-dependent kinase inhibitor p27Kip1 expression and proliferation in non-Hodgkin's lymphoma: independent prognostic value of p27Kip1

The cyclin-dependent kinase inhibitor p27Kip1 is a negative cell cycle regulator linking extracellular growth-regulatory signals to the cell cycle machinery in G1. We investigated the pattern and prognostic value of p27Kip1 expression in a population-based group of 203 non-Hodgkin's lymphoma (NHL) patients. The expression of p27Kip1 was identified by immunohistochemistry and correlated with Ki-67 expression and clinical features. Correlation with outcome was determined using uni- and multivariate analysis stratified by clinical grade. Except for very aggressive NHL, there was a negative correlation between p27Kip1 and Ki-67 expression. Low expression of p27Kip1, defined as nuclear p27Kip1 expression in <40% of malignant cells, was predictive of poor survival in indolent and aggressive NHL. However, even in this regard, very aggressive lymphomas behaved differently as those with low p27Kip1 expression tended to do better. Likewise, a high proliferation rate (Ki-67 >40%) was associated with poor survival in indolent and aggressive lymphomas. Multivariate analysis using the proportional hazards model showed that only p27Kip1, and not Ki-67, maintained independent prognostic significance in indolent and aggressive lymphomas (relative risk = 2. 0; P = 0.0095). The low cost and simplicity of this standard immunohistochemistry analysis makes p27Kip1 a promising and suitable prognostic marker in routine diagnostic laboratories in a standard diagnostic panel.

New chicken Rfp-Y haplotypes on the basis of MHC class II RFLP and MLC analyses

New chicken Rfp-Y haplotypes were determined by the use of restriction fragment length polymorphism (RFLP) and mixed lymphocyte culture (MLC) in four different chicken haplotypes, B15, B19, B21, B201. The RFLP polymorphism was mapped to the Rfp-Y system by the use of a subclone (18.1) which maps near a polymorphic lectin gene located in the Rfp-Y system and DNA from families with known segregation of the implicated RFLP polymorphism. For the first time it is shown that major histocompatibility complex class II genes in the Rfp-Y system have functional implications. Sequence information of the B1 domain of the proposed Rfp-Y haplotypes was obtained which supported the functional data.

Prevalence of angioid streaks and other ocular complications of Paget's disease of bone

Seventy randomly selected patients with Paget's disease of bone were examined for ocular complications. The prevalence of macular degeneration and cataract was 24.3%. Only one patient was found to have angioid streaks. Eight patients had peripapillary chorioretinal atrophy. These findings suggest that the prevalence of serious ocular complications of Paget's disease is not as high as previously thought. The significance of peripapillary chorioretinal atrophy requires further evaluation.