The plasma levels of coglutinin are heritable in cattle and low levels predispose to infection

Calves severely affected by bovine respiratory disease have reduced protection against histone toxicity and exhibit lower complement activity

Bovine respiratory disease (BRD) remains the greatest challenge facing the beef industry. Calves affected by BRD can manifest illness ranging from subclinical infection to acute death. In pathologies similar to BRD, extracellular histones have been implicated as major contributors to lung tissue damage. Histones are basic proteins responsible for DNA organization in cell nuclei, however when released extracellularly during cell injury or via neutrophil activation they become cytotoxic. Cattle suffering severe cases of BRD demonstrate reduced capacity to protect against the cytotoxic effects of histones, however, the protective mechanism(s) of serum remain(s) unknown. Therefore, the objective was to identify components within serum that contribute to protection against histone toxicity. Serum proteins from animals considered protective (P; N = 4) and nonprotective (NP; N = 4) against the toxic effects of histones were precipitated by the addition and incubation of exogenous histones. Proteins that interact with histones from both groups were isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified via label free "shotgun" proteomics. Sixteen candidate proteins increased by ≥2-fold change in P vs. NP animals were identified, with several associated with the complement system. A subsequent study was conducted to evaluate complement system activity and serum protective capacity against exogenous histones in feedlot heifers. Serum samples were collected from 118 heifer calves (BW at arrival = 229 ± 2.4 kg) at feedlot arrival. Animals were retrospectively assigned to groups consisting of: calves not requiring treatment with antibiotics for BRD (CONT; N = 80), calves treated once (1TRT; N = 21), calves treated twice (2TRT; N = 5), calves treated thrice (3TRT; N = 3), or calves that died from BRD within 1 wk of entering the feedlot (DA; N = 9). Serum from DA animals was less protective than CONT (P = 0.0005) animals against histone toxicity. Complement activity of DA animals was reduced compared to CONT (P = 0.0044) animals. Additionally, the use of both assays as a ratio resulted in increased ability to detect DA animals. Results suggest that cattle predisposed to severe cases of respiratory disease may have impaired complement activity presumably contributing to reduced protective capacity against histone toxicity.

Host Serum Proteins as Potential Biomarkers of Bovine Tuberculosis Resistance Phenotype

Eradication of bovine tuberculosis (bTB) continues to be a worldwide challenge. The lack of reliable vaccines dampens the control and eradication programs of Mycobacterium bovis infection and spread. Selection and breeding of cattle resistant to M. bovis infection would greatly enhance the effectiveness of bTB eradication programs. Here, we have evaluated the potential of serum proteins as biomarkers of cattle resistance to bTB in Holstein-Friesian cows, 6-8-year-old, born and raised in similar conditions in herds with bTB prevalence >30%. Serum proteins obtained from uninfected cows (bTB-resistant; R) were compared to those from infected cows (bTB-susceptible; S), defined by a negative or positive bTB diagnosis, respectively. bTB diagnosis included: (i) single intradermal (caudal fold) tuberculin test, (ii) whole blood IFN-gamma test, (iii) gross visible lesions in lymph nodes and lungs by inspection at the abattoir, and (iv) a bacteriological culture for M. bovis. Using 2D-GE and LC-ESI-MS/MS, we found higher expression levels of primary amine oxidase (AO), complement component 5 (C5), and serotransferrin (TF) in R cattle than S cattle. In-house developed and standardized ELISAs for these novel biomarkers showed the best sensitivities of 72, 77, 77%, and specificities of 94, 94, 83%, for AO, C5, and TF, respectively. AUC-ROC (95% CI) values of 0.8935 (0.7906-0.9964), 0.9290 (0.8484-1.010), and 0.8580 (0.7291-0.9869) were obtained at cut-off points of 192.0, 176.5 ng/ml, and 2.1 mg/ml for AO, C5, and TF, respectively. These proteins are involved in inflammatory/immunomodulatory responses to infections and may provide a novel avenue of research to determine the mechanisms of protection against bTB. Overall, our results indicate that these proteins could be novel biomarkers to help identify cattle resistant to bTB, which in turn could be used to strengthen the effectiveness of existing eradication programs against bTB.

Innate Immune Pattern Recognition Receptors of Mycobacterium tuberculosis: Nature and Consequences for Pathogenesis of Tuberculosis

Innate immunity against Mycobacterium tuberculosis is a critical early response to prevent the establishment of the infection. Despite recent advances in understanding the host-pathogen dialogue in the early stages of tuberculosis (TB), much has yet to be learnt. The nature and consequences of this dialogue ultimately determine the path of infection: namely, either early clearance of M. tuberculosis, or establishment of M. tuberculosis infection leading to active TB disease and/or latent TB infection. On the frontline in innate immunity are pattern recognition receptors (PRRs), with soluble factors (e.g. collectins and complement) and cell surface factors (e.g. Toll-like receptors and other C-type lectin receptors (Dectin 1/2, Nod-like receptors, DC-SIGN, Mincle, mannose receptor, and MCL) that play a central role in recognising M. tuberculosis and facilitating its clearance. However, in a 'double-edged sword' scenario, these factors can also be involved in enhancement of pathogenesis as well. Furthermore, innate immunity is also a critical bridge in establishing the subsequent adaptive immune response, which is also responsible for granuloma formation that cordons off M. tuberculosis infection, establishing latency and acting as a reservoir for bacterial persistence and dissemination of future disease. This chapter discusses the current understanding of pattern recognition of M. tuberculosis by innate immunity and the role this plays in the pathogenesis and protection against TB.

Collectins: Innate Immune Pattern Recognition Molecules

Collectins are collagen-containing C-type (calcium-dependent) lectins which are important pathogen pattern recognising innate immune molecules. Their primary structure is characterised by an N-terminal, triple-helical collagenous region made up of Gly-X-Y repeats, an a-helical coiled-coil trimerising neck region, and a C-terminal C-type lectin or carbohydrate recognition domain (CRD). Further oligomerisation of this primary structure can give rise to more complex and multimeric structures that can be seen under electron microscope. Collectins can be found in serum as well as in a range of tissues at the mucosal surfaces. Mannanbinding lectin can activate the complement system while other members of the collectin family are extremely versatile in recognising a diverse range of pathogens via their CRDs and bring about effector functions designed at the clearance of invading pathogens. These mechanisms include opsonisation, enhancement of phagocytosis, triggering superoxidative burst and nitric oxide production. Collectins can also potentiate the adaptive immune response via antigen presenting cells such as macrophages and dendritic cells through modulation of cytokines and chemokines, thus they can act as a link between innate and adaptive immunity. This chapter describes the structure-function relationships of collectins, their diverse functions, and their interaction with viruses, bacteria, fungi and parasites.

Functional characterization of partial recombinant goat conglutinin: Its role as innate immunity marker and use as antigen in sandwich ELISA

Conglutinin, a liver synthesized versatile innate immune marker consisting C-type lectin domain belongs to collectin superfamily of proteins. The protein, first detected in bovine serum as soluble pattern recognition receptor (PRR) has wide range of antimicrobial activities. In the present study, open reading frame (ORF) encoding neck and carbohydrate recognition domain (NCRD) of goat conglutinin gene ligated to the vector pRSET-A was expressed in E. coli BL-21(pLys) cells. The 27 kDa recombinant protein (rGCGN) purified by single step Ni⁺² -NTA affinity chromatography was found to cross-react with recombinant anti-buffalo conglutinin antibody raised in poultry. Further, it displayed calcium-dependant sugar binding activity towards yeast mannan and calcium-independent binding activity towards LPS. The mannan binding activity of rGCGN was inhibited in the presence of N-acetyl-glucosamine because of higher affinity towards this sugar. The recombinant protein was found to stimulate production of superoxide ions and hydrogen peroxide in goat neutrophils, which are instrumental in stimulating phagocytic activity of cells. When used as antigen in Sandwich ELISA, straight line (Y = 0.299x + 0.067, R² = 0.997) was observed within the concentration range of 200-1000 ng/100 μl of rGCGN. Using this equation, the native conglutinin concentration in goat sera was estimated to be 0.5-7.5 μg/ml. The results indicated that prokaryotically expressed functionally active rGCGN can be used as antigen to assess native serum conglutinin levels in Sandwich ELISA and as immunomodulator in therapeutic applications to sequester unwanted immune complexes from the circulation.

Atomic-resolution crystal structures of the immune protein conglutinin from cow reveal specific interactions of its binding site with N-acetylglucosamine

Bovine conglutinin is an immune protein that is involved in host resistance to microbes and parasites and interacts with complement component iC3b, agglutinates erythrocytes, and neutralizes influenza A virus. Here, we determined the high-resolution (0.97–1.46 Å) crystal structures with and without bound ligand of a recombinant fragment of conglutinin's C-terminal carbohydrate-recognition domain (CRD). The structures disclosed that the high-affinity ligand N-acetyl-d-glucosamine (GlcNAc) binds in the collectin CRD calcium site by interacting with the O3′ and O4′ hydroxyls alongside additional specific interactions of the N-acetyl group oxygen and nitrogen with Lys-343 and Asp-320, respectively. These residues, unique to conglutinin and differing both in sequence and in location from those in other collectins, result in specific, high-affinity binding for GlcNAc. The binding pocket flanking residue Val-339, unlike the equivalent Arg-343 in the homologous human surfactant protein D, is sufficiently small to allow conglutinin Lys-343 access to the bound ligand, whereas Asp-320 lies in an extended loop proximal to the ligand-binding site and bounded at both ends by conserved residues that coordinate to both calcium and ligand. This loop becomes ordered on ligand binding. The electron density revealed both α and β anomers of GlcNAc, consistent with the added α/βGlcNAc mixture. Crystals soaked with α1–2 mannobiose, a putative component of iC3b, reported to bind to conglutinin, failed to reveal bound ligand, suggesting a requirement for presentation of mannobiose as part of an extended physiological ligand. These results reveal a highly specific GlcNAc-binding pocket in conglutinin and a novel collectin mode of carbohydrate recognition.

Complement Dependent and Independent Interaction Between Bovine Conglutinin and Mycobacterium bovis BCG: Implications in Bovine Tuberculosis

Bovine conglutinin, the first animal collectin to be discovered, is structurally very similar to Surfactant Protein D (SP-D). SP-D is known to interact with Mycobacterium tuberculosis, and the closely-related M. bovis, the causative agent of bovine tuberculosis. We speculated that due to the overall similarities between conglutinin and SP-D, conglutinin is likely to have a protective influence in bovine tuberculosis. We set out to investigate the role of conglutinin in host-pathogen interaction during mycobacterial infection. We show here that a recombinant truncated form of conglutinin (rfBC), composed of the neck and C-type lectin domains, binds specifically and in a dose-dependent manner to the model organism Mycobacterium bovis BCG. rfBC showed a significant direct bacteriostatic effect on the growth of M. bovis BCG in culture. In addition, rfBC inhibited the uptake of M. bovis BCG by THP-1 macrophages (human monocyte lineage cell line) and suppressed the subsequent pro-inflammatory response. Conglutinin is well-known as a binder of the complement activation product, iC3b. rfBC was also able to inhibit the uptake of complement-coated M. bovis BCG by THP-1 macrophages, whilst modulating the pro-inflammatory response. It is likely that rfBC inhibits the phagocytosis of mycobacteria by two distinct mechanisms: firstly, rfBC interferes with mannose receptor-mediated uptake by masking lipoarabinomannan (LAM) on the mycobacterial surface. Secondly, since conglutinin binds iC3b, it can interfere with complement receptor-mediated uptake via CR3 and CR4, by masking interactions with iC3b deposited on the mycobacterial surface. rfBC was also able to modulate the downstream pro-inflammatory response in THP-1 cells, which is important for mobilizing the adaptive immune response, facilitating containment of mycobacterial infection. In conclusion, we show that conglutinin possesses complement-dependent and complement-independent anti-mycobacterial activities, interfering with both known mechanisms of mycobacterial uptake by macrophages. As mycobacteria are specialized intracellular pathogens, conglutinin may inhibit M. bovis and M. tuberculosis from establishing an intracellular niche within macrophages, and thus, negatively affect the long-term survival of the pathogen in the host.

Identification of polymorphisms in the bovine collagenous lectins and their association with infectious diseases in cattle

Infectious diseases are a significant issue in animal production systems, including both the dairy and beef cattle industries. Understanding and defining the genetics of infectious disease susceptibility in cattle is an important step in the mitigation of their impact. Collagenous lectins are soluble pattern recognition receptors that form an important part of the innate immune system, which serves as the first line of host defense against pathogens. Polymorphisms in the collagenous lectin genes have been shown in previous studies to contribute to infectious disease susceptibility, and in cattle, mutations in two collagenous lectin genes (MBL1 and MBL2) are associated with mastitis. To further characterize the contribution of variation in the bovine collagenous lectins to infectious disease susceptibility, we used a pooled NGS approach to identify short nucleotide variants (SNVs) in the collagenous lectins (and regulatory DNA) of cattle with (n = 80) and without (n = 40) infectious disease. Allele frequency analysis identified 74 variants that were significantly (p < 5 × 10⁻⁶) associated with infectious disease, the majority of which were clustered in a 29-kb segment upstream of the collectin locus on chromosome 28. In silico analysis of the functional effects of all the variants predicted 11 SNVs with a deleterious effect on protein structure and/or function, 148 SNVs that occurred within potential transcription factor binding sites, and 31 SNVs occurring within potential miRNA binding elements. This study provides a detailed look at the genetic variation of the bovine collagenous lectins and identifies potential genetic markers for infectious disease susceptibility.

Quantitative genetic analysis of the bTB diagnostic single intradermal comparative cervical test (SICCT)

BACKGROUND

Bovine tuberculosis (bTB) is a disease of significant economic importance and is a persistent animal health problem with implications for public health worldwide. Control of bTB in the UK has relied on diagnosis through the single intradermal comparative cervical test (SICCT). However, limitations in the sensitivity of this test hinder successful eradication and the control of bTB remains a major challenge. Genetic selection for cattle that are more resistant to bTB infection can assist in bTB control. The aim of this study was to conduct a quantitative genetic analysis of SICCT measurements collected during bTB herd testing. Genetic selection for bTB resistance will be partially informed by SICCT-based diagnosis; therefore it is important to know whether, in addition to increasing bTB resistance, this might also alter genetically the epidemiological characteristics of SICCT.

RESULTS

Our main findings are that: (1) the SICCT test is robust at the genetic level, since its hierarchy and comparative nature provide substantial protection against random genetic changes that arise from genetic drift and from correlated responses among its components due to either natural or artificial selection; (2) the comparative nature of SICCT provides effective control for initial skin thickness and age-dependent differences; and (3) continuous variation in SICCT is only lowly heritable and has a weak correlation with SICCT positivity among healthy animals which was not significantly different from zero (P > 0.05). These emerging results demonstrate that genetic selection for bTB resistance is unlikely to change the probability of correctly identifying non-infected animals, i.e. the test's specificity, while reducing the overall number of cases.

CONCLUSIONS

This study cannot exclude all theoretical risks from selection on resistance to bTB infection but the role of SICCT in disease control is unlikely to be rapidly undermined, with any adverse correlated responses expected to be weak and slow, which allow them to be monitored and managed.

Sequence-based appraisal of the genes encoding neck and carbohydrate recognition domain of conglutinin in blackbuck (Antilope cervicapra) and goat (Capra hircus)

Conglutinin, a collagenous C-type lectin, acts as soluble pattern recognition receptor (PRR) in recognition of pathogens. In the present study, genes encoding neck and carbohydrate recognition domain (NCRD) of conglutinin in goat and blackbuck were amplified, cloned, and sequenced. The obtained 488 bp ORFs encoding NCRD were submitted to NCBI with accession numbers KC505182 and KC505183. Both nucleotide and predicted amino acid sequences were analysed with sequences of other ruminants retrieved from NCBI GenBank using DNAstar and Megalign5.2 software. Sequence analysis revealed maximum similarity of blackbuck sequence with wild ruminants like nilgai and buffalo, whereas goat sequence displayed maximum similarity with sheep sequence at both nucleotide and amino acid level. Phylogenetic analysis further indicated clear divergence of wild ruminants from the domestic ruminants in separate clusters. The predicted secondary structures of NCRD protein in goat and blackbuck using SWISSMODEL ProtParam online software were found to possess 6 beta-sheets and 3 alpha-helices which are identical to the result obtained in case of sheep, cattle, buffalo, and nilgai. However, quaternary structure in goat, sheep, and cattle was found to differ from that of buffalo, nilgai, and blackbuck, suggesting a probable variation in the efficiency of antimicrobial activity among wild and domestic ruminants.

Genes controlling vaccine responses and disease resistance to respiratory viral pathogens in cattle

Farm animals remain at risk of endemic, exotic and newly emerging viruses. Vaccination is often promoted as the best possible solution, and yet for many pathogens, either there are no appropriate vaccines or those that are available are far from ideal. A complementary approach to disease control may be to identify genes and chromosomal regions that underlie genetic variation in disease resistance and response to vaccination. However, identification of the causal polymorphisms is not straightforward as it generally requires large numbers of animals with linked phenotypes and genotypes. Investigation of genes underlying complex traits such as resistance or response to viral pathogens requires several genetic approaches including candidate genes deduced from knowledge about the cellular pathways leading to protection or pathology, or unbiased whole genome scans using markers spread across the genome. Evidence for host genetic variation exists for a number of viral diseases in cattle including bovine respiratory disease and anecdotally, foot and mouth disease virus (FMDV). We immunised and vaccinated a cattle cross herd with a 40-mer peptide derived from FMDV and a vaccine against bovine respiratory syncytial virus (BRSV). Genetic variation has been quantified. A candidate gene approach has grouped high and low antibody and T cell responders by common motifs in the peptide binding pockets of the bovine major histocompatibility complex (BoLA) DRB3 gene. This suggests that vaccines with a minimal number of epitopes that are recognised by most cattle could be designed. Whole genome scans using microsatellite and single nucleotide polymorphism (SNP) markers has revealed many novel quantitative trait loci (QTL) and SNP markers controlling both humoral and cell-mediated immunity, some of which are in genes of known immunological relevance including the toll-like receptors (TLRs). The sequencing, assembly and annotation of livestock genomes and is continuing apace. In addition, provision of high-density SNP chips should make it possible to link phenotypes with genotypes in field populations without the need for structured populations or pedigree information. This will hopefully enable fine mapping of QTL and ultimate identification of the causal gene(s). The research could lead to selection of animals that are more resistant to disease and new ways to improve vaccine efficacy.

Conglutinin - an Important Element of Natural Immunity in Ruminants (a Review)

Conglutinin represents a collectin appearing only in some mammals, including cattle. It plays an important role in resistance of hosts against microbes and parasites. It exhibits affinity toward saccharides present on the surface of bacteria, viruses, fungi and parasites and it mobilizes the mechanisms leading to their inactivation. It manifests also the unique ability of agglutinating complement- and antibody-coated erythrocytes. Moreover, it shows the ability to activate immune system cells, including the process of phagocytosis. In this review also the factors that determine the amount and activity of conglutinin in mammalian serum were presented, including environmental conditions and infectious agents, such as various types of bacteria and viruses. The broad scope of conglutinin is genetically controlled and, therefore, this collectin may constitute a useful and crucial factor in cattle husbandry.

Plasma ladderlectin concentration following sterile inflammation and Aeromonas salmonicida subsp. salmonicida infection

Plasma samples obtained from rainbow trout either experimentally infected with Aeromonas salmonicida or injected with either A. salmonicida lipopolysaccharide (LPS) or a commercial A. salmonicida vaccine (Lipogen) were analysed by enzyme immunoassay to evaluate changes in rainbow trout ladderlectin (RTLL) concentrations during the acute phase response (APR). Plasma RTLL concentrations in fish injected with A. salmonicida LPS, vaccine or live A. salmonicida varied over a 10 day period, but did not significantly increase. In contrast, fish experimentally infected with A. salmonicida exhibited a modest, but statistically significant (P < 0.05), decrease in RTLL concentration. These studies demonstrate that RTLL is not detectably induced during the trout APR to sterile inflammation or A. salmonicida infection, but plasma concentration of this protein may be reduced during bacterial infection.

Bacterial-binding activity and plasma concentration of ladderlectin in rainbow trout (Oncorhynchus mykiss)

Soluble, defense lectins bind conserved microbial patterns leading to pathogen opsonization, enhanced phagocytosis and activation of complement. These immune functions, however, vary widely among individuals due to genetic and acquired differences affecting binding capacity or plasma concentration. Most evidence for the defensive function of soluble lectins is based on mammals, but several functionally homologous, but less well-characterized, lectins have been identified in fish. In this study, we compared binding of rainbow trout plasma ladderlectin to relevant, intact bacterial targets. A polyclonal antiserum raised against a synthetic peptide identical to the 20 N-terminal amino acids of the reduced 16 kDa rainbow trout ladderlectin subunit was used to detect plasma ladderlectin in immunoblots and indirect enzyme-linked immunosorbent assay (ELISA). Ladderlectin binding to Aeromonas salmonicida subsp. salmonicida, Aeromonas hydrophila, Yersinia ruckeri and Pseudomonas sp. was detected by PAGE and immunoblots of saccharide elutions from intact bacteria incubated in the presence of normal trout plasma. Although plasma concentrations of immunoreactive ladderlectin were low in the majority of trout, significant (P < 0.0001) variation between individual fish was observed in two separate populations. In addition, one population demonstrated a subset of individuals whose ladderlectin levels were approximately seven-fold higher than the population median. These findings indicate that rainbow trout have variable amounts of plasma ladderlectin capable of binding to the surfaces of several relevant bacterial targets.

Anti-influenza A virus activities of mannan-binding lectins and bovine conglutinin

Mannan-binding lectin (MBL) and bovine conglutinin (BKg) belong to the collectin family, which is involved in first-line host defense against various infectious agents. We have previously reported that human MBL inhibited type A influenza viral hemagglutination, infection and spreading to adjacent cells without complement activation. In this study, we investigated the direct antiviral activities of bovine MBL, rabbit MBL and BKg. All collectins used in this study inhibited viral infectivity and hemagglutination at concentrations of 0.02-0.3 microg/ml. They also demonstrated inhibitory activity against viral spreading. Like human MBL, bovine MBL and BKg showed antiviral activities at their physiological concentrations. These results suggest that mammalian MBLs and BKg may inhibit the spread of influenza A virus through the bloodstream.

Genetic variation and responses to vaccines

Disease is a major source of economic loss to the livestock industry. Understanding the role of genetic factors in immune responsiveness and disease resistance should provide new approaches to the control of disease through development of safe synthetic subunit vaccines and breeding for disease resistance. The major histocompatibility complex (MHC) has been an important candidate locus for immune responsiveness studies. However, it is clear that other loci play an important role. Identifying these and quantifying the relative importance of MHC and non-MHC genes should result in new insights into host–pathogen interactions, and information that can be exploited by vaccine designers. The rapidly increasing information available about the bovine genome and the identification of polymorphisms in immune-related genes will offer potential candidates that control immune responses to vaccines. The bovine MHC,BoLA, encodes two distinct isotypes of class II molecules, DR and DQ, and in about half the common haplotypes theDQgenes are duplicated and expressed. DQ molecules are composed of two polymorphic chains whereas DR consists of one polymorphic and one non-polymorphic chain. Although, it is clear that MHC polymorphism is related to immune responsiveness, it is less clear how different allelic and locus products influence the outcome of an immune response in terms of generating protective immunity in outbred animals. A peptide derived from foot-and-mouth disease virus (FMDV) was used as a probe for BoLA class II function. Both DR and DQ are involved in antigen presentation. In an analysis of T-cell clones specific for the peptide, distinct biases to particular restriction elements were observed. In addition inter-haplotype pairings of DQA and DQB molecules produced functional molecules, which greatly increases the numbers of possible restriction elements, compared with the number of genes, particularly in cattle with duplicatedDQgenes. In a vaccine trial with several peptides derived from FMDV,BoLAclass IIDRB3polymorphisms were correlated with both protection and non-protection. Although variation in immune responsiveness to the FMDV peptide between different individuals is partly explainable byBoLAclass II alleles, other genetic factors play an important role. In a quantitative trait locus project, employing a second-generation cross between Charolais and Holstein cattle, significant sire and breed effects were also observed in T-cell, cytokine and antibody responses to the FMDV peptide. These results suggest that both MHC and non-MHC genes play a role in regulating bovine immune traits of relevance to vaccine design. Identifying these genes and quantifying their relative contributions is the subject of further studies.

Passive and active components of neonatal innate immune defenses

Innate immune defenses are crucial for survival in the first days and weeks of life. At birth, newborns are confronted with a vast array of potentially pathogenic microorganisms that were not encountered in utero. At this age, cellular components of the adaptive immune system are in a naive state and are slow to respond. Antibodies received from the dam are essential for defense, but represent a finite and dwindling resource. Innate components of the immune system detect pathogen-associated molecular patterns (PAMPs) on microorganisms (and their products) by means of pattern-recognition receptors (PRRs). Soluble mediators of the innate system such as complement proteins, pentraxins, collectins, ficolins, defensins, lactoferrin, lysozyme etc. can bind to structures on pathogens, leading to agglutination, interference with receptor binding, opsonization, neutralization, direct membrane damage and recruitment of additional soluble and cellular elements through inflammation. Cell-associated receptors such as the Toll-like receptors (TLRs) can activate cells and coordinate responses (both innate and adaptive). In this paper, accumulated knowledge of the receptors, soluble and cellular elements that contribute to innate defenses of young animals is reviewed. Research interest in this area has been intermittent, and the literature varies in quantity and quality. It is hoped that documentation of the limitations of our knowledge base will lead to more extensive and enlightening studies.

Comparative genetics and innate immune functions of collagenous lectins in animals

Collagenous lectins such as mannan-binding lectins (MBLs), ficolins (FCNs), surfactant proteins A and D (SP-A, SP-D), conglutinin (CG), and related ruminant lectins are multimeric proteins with carbohydrate-binding domains aligned in a manner that facilitates binding to microbial surface polysaccharides. MBLs and FCNs are structurally related to C1q, but activate the lectin complement pathway via interaction with MBL-associated serine proteases (MASPs). MBLs, FCNs, and other collagenous lectins also bind to some host macromolecules and contribute to their removal. While there is evidence that some lectins and the lectin complement pathway are conserved in vertebrates, many differences in collagenous lectins have been observed among humans, rodents, and other vertebrates. For example, humans have only one MBL but three FCNs, whereas most other species express two FCNs and two MBLs. Bovidae express CG and other SP-D-related collectins that are not found in monogastric species. Some dysfunctions of human MBL are due to single nucleotide polymorphisms (SNPs) that affect its expression or structure and thereby increase susceptibility to some infections. Collagenous lectins have well-established roles in innate immunity to various microorganisms, so it is possible that some lectin genotypes or induced phenotypes influence resistance to some infectious or inflammatory diseases in animals.

Surfactant protein D in newborn infants: factors influencing surfactant protein D levels in umbilical cord blood and capillary blood

Surfactant protein D (SP-D) is a collectin that plays an important role in the innate immune system. The role of SP-D in the metabolism of surfactant is as yet quite unclear. The aims of this study were to establish normal values of SP-D in the umbilical cord blood and capillary blood of mature newborn infants and to assess the influence of perinatal conditions on these levels. A total of 458 infants were enrolled in the present study. Umbilical cord blood was drawn at the time of birth and capillary blood at age 4 to 10 d. The concentration of SP-D in umbilical cord blood and capillary blood was measured by enzyme-linked immunosorbent assay. The median concentration of SP-D in umbilical cord blood was 392.1 ng/mL and was found to be influenced by maternal smoking and labor. The median concentration of SP-D in capillary blood was 777.5 ng/mL and was found to be influenced by the mode of delivery, the highest levels being observed in infants born by cesarean section. It was concluded that SP-D concentrations in umbilical cord blood and capillary blood are highly variable and depend on several perinatal conditions. Further studies are needed to elucidate the effect of respiratory distress and infection on SP-D concentrations.

Bos taurus and Bos indicus (Sahiwal) calves respond differently to infection with Theileria annulata and produce markedly different levels of acute phase proteins

Disease-resistant livestock could provide a potentially sustainable and environmentally sound method of controlling tick and tick-borne diseases of livestock in the developing world. Advances in the knowledge and science of genomics open up opportunities to identify selectable genes controlling disease resistance but first, breeds and individuals with distinguishable phenotypes need to be identified. The Bos indicus breed, Sahiwal, has been exploited in dairy breeding programmes, because it is resistant to ticks and has relatively good performance characteristics compared to other indigenous cattle breeds of tropical regions. The analyses reported here show that Sahiwal calves were also more resistant than European Bos taurus (Holstein) dairy breed calves to tick-borne tropical theileriosis (Theileria annulata infection). Following experimental infection with T. annulata sporozoites, a group of Sahiwal calves all survived without treatment, with significantly lower maximum temperatures (P<0.01) and lower rates of parasite multiplication (P<0.05) than a group of Holstein calves, which all had severe responses. Although the Sahiwals became as anaemic as the Holsteins, other measures of pathology, including enlargement of the draining lymph node and the acute phase proteins, alpha1 acid glycoprotein and haptoglobin, were significantly less in the Sahiwals than in the Holsteins (P<0.05). Additionally, the Sahiwals had significantly lower resting levels of alpha1 acid glycoprotein than the Holsteins (P<0.05). Production of a third acute phase proteins, serum amyloid A, had very similar kinetics in both breeds. Acute phase proteins are produced in response to systemic release of the kinds of pro-inflammatory cytokines that are thought to be responsible for the pyrexic, cachectic and anorexic responses characteristic of tropical theileriosis. The prolonged production of alpha1 acid glycoprotein in the Holsteins is indicative of chronic production of circulating pro-inflammatory cytokines. In contrast, Sahiwals appear able to overcome infection with T. annulata as well as limit pathology by preventing the over-stimulation of pathways involving these cytokines.

A time-resolved immunofluorometric assay for quantification of collectin-43

CL-43 is a serum collectin involved in the innate immunity of cattle and variability of serum CL-43 may relate to disease in cows. A high capacity time-resolved immunofluorometric assay (TRIFMA) for the bovine collectin-43 (CL-43) was developed. The TRIFMA was constructed as a noncompetitive sandwich based on polyclonal antibodies and a novel monoclonal antibody (mab) raised against CL-43 and was set up to run on an automatic analyser designed for the TRIFMA detection system. The polyclonal antibodies were immobilized on microtiter plate wells and incubated with diluted plasma samples, including quality controls (QC) and dilutions of a plasma with known CL-43 concentration. CL-43 was sandwiched between the capture antibodies and the monoclonal antibody and the detection was optimised with biotin-labelled secondary antibodies and streptavidin-Eu3+. Plates were washed four times between each step and finally incubated with enhancement solution before measuring the fluorescence. The assay detection limit was 0.24 ng/ml and the working range was 0.54-22 ng/ml. Recovery was 92.3% when samples were spiked with 2.0 ng/ml of CL-43. Intraplate and interplate coefficients of variation were in the range of 1.11-2.36% and 0.70-1.35%, respectively. No circadian rhythm (24-h variation) in CL-43 plasma levels was observed, indicating that plasma levels were not influenced by e.g. feeding. Samples could be stored at -20 degrees C and were not sensitive to repeated freezing and thawing. In conclusion, the developed TRIFMA for CL-43 is specific and reliable over a measurement range covering most situations.

The genes encoding bovine SP-A, SP-D, MBL-A, conglutinin, CL-43 and CL-46 form a distinct collectin locus onBos tauruschromosome 28 (BTA28) at position q.1.8-1.9

Collectins are a group of C-type lectins involved in the innate immune system, where they mediate and modulate clearance of pathogens. The health status of cattle is of major economical and ethical concern; therefore, the study of bovine collectins is of importance. The collectins conglutinin, CL-43 and CL-46 are only present in Bovidae and the characterization of their genes indicates that they are structural descendants of another collectin, lung surfactant protein D (SP-D). In this study, we assembled BAC clones into a contig spanning 330-1150 kb, which includes the bovine genes encoding the collectins SP-A (SFTPA), SP-D (SFTPD), mannan-binding lectin A (MBL1), CL-43 (COLEC9), CL-46 (COLEC13) and conglutinin (COLEC8). In the same contig, we also identified a gene that potentially encodes a novel conglutinin-like collectin (COLEC14). The arrangement of STFPA, SFTPD and MBL1 is homologous to the organization found in humans and mice, whereas the Bovidae-specific collectin genes, COLEC8, COLEC9 and COLEC13, extend from SFTPD. Proximal to the collectin locus at BTA28q1.8-1.9, and included in the contig, we found the microsatellite IDVGA8, which may be a valuable marker for tracking polymorphisms in the linked collectin genes.

A time-resolved immunofluorometric assay for quantification of the bovine collectin conglutinin

A high capacity time-resolved immunofluorometric assay (TRIFMA) for the bovine collectin conglutinin was developed. The TRIFMA was constructed as a non-competitive sandwich assay based on polyclonal antibodies as the capture reagent and a novel monoclonal antibody raised against conglutinin as the detection reagent and was set up to run on an automatic analyzer designed for the TRIFMA detection system. Polyclonal antibodies immobilized on microtiter plate wells were incubated overnight at 4 degrees C with diluted plasma samples, including quality controls (QC) and dilutions of a plasma with known conglutinin concentration. Conglutinin was sandwiched between the capture antibodies and the monoclonal antibody and the detection optimised with biotin-labelled secondary antibodies and streptavidin-Eu(3+). Plates were washed four times between each step and finally incubated with enhancement solution before measuring the fluorescence. The assay detection limit was 0.34 ng/ml and the working range 0.80 ng/ml-0.20 microg/ml. Intra-plate and inter-plate coefficients of variation (CV) were in the range of 5.0-8.3% and 6.2-7.2%, respectively, at concentrations of 3.4 and 150 ng/ml. Recovery was 90.9+/-2.4% and 98.8+/-2.5% when samples were spiked with 20 ng/ml and 100 ng/ml purified bovine conglutinin (BK). No circadian rhythm (24-h variation) in conglutinin plasma levels was observed across animals, indicating that the plasma levels were not influenced by, e.g. feeding. Samples could be stored at -20 degrees Celsius and were not sensitive to repeated freezing and thawing. In conclusion, the developed TRIFMA for bovine conglutinin is specific and reliable over a measurement range covering most situations.

Conglutinin and immunoconglutinin titers in stressed calves in a feedlot

OBJECTIVE

To determine whether increased conglutinin titers are evident in stressed calves that do not develop respiratory tract disease in feedlots, compared with respiratory tract disease, and to determine the increase in immunoconglutinin titers.

ANIMALS

101 mixed-breed beef calves.

PROCEDURE

Calves were processed at 4 farms of origin and allowed to remain with their dams for another 100 days. Calves from each farm were brought to a centrally located order-buyer barn. In a feedlot, 101 calves were assigned to pens and observed daily for clinical signs of acute respiratory tract disease. When sick calves were detected, they were treated with antibiotics and isolated in a pen for 4 days. Conglutinin and immunoconglutinin titers were determined for all calves.

RESULTS

During the 28-day study, 73 calves developed respiratory tract disease, whereas 28 calves remained healthy. Mean conglutinin titers differed significantly among calves from the 4 farms. Significant differences were not detected in conglutinin titers among calves on the basis of sex, morbidity, or vaccination status against Mannheimia haemolytica at each farm, the order-buyer barn, or the feedlot on days 8, 15, and 28 after arrival. Immunoconglutinin titers in calves differed significantly among farms and morbidity status.

CONCLUSIONS AND CLINICAL RELEVANCE

Mean conglutinin titers in calves do not appear to be associated with the incidence of acute respiratory tract disease; however, increased immunoconglutinin titers appear to be associated with recovery of stressed calves from respiratory tract disease during the first 15 days after arrival in a feedlot.

Mannan-binding lectin (MBL) in chickens: molecular and functional aspects

Mannan-binding lectin (MBL) is a serum collectin (i.e. mosaic protein with collagenous and lectin domains) involved in the innate immune defence against various microbes. In vitro studies indicate that MBL exerts its function by binding to the microbial surface through its carbohydrate recognition domains followed by direct opsonization or complement activation via the MBL associated serine proteases MASP-1 and MASP-2. In Aves (i.e. chickens), as in man, only one MBL form has been found, while traditional laboratory animals (i.e. mouse and rat) have two MBL forms in serum. MBL has been extensively studied in mammals but recently also in Aves. This review summarizes the present knowledge of MBL in chickens and compares it to the situation in mammals.

Structural aspects of collectins and receptors for collectins

The collectins are oligomeric molecules composed of C-type lectin domains attached to collagen regions via alpha-coiled neck regions. Five members of the collectins have been characterized. Mannan-binding lectin (MBL), conglutinin and collectin-43 (CL-43) are serum proteins produced by the liver. Lung surfactant protein A (SP-A) and lung surfactant protein D (SP-D) are mainly found in the lung, where they are synthesized by alveolar type II cells and secreted to the alveolar surface. The collectins are believed to play an important role in innate immunity. They bind oligosaccharides on the surface of a variety of microbial pathogens. After binding of the collectins to the microbial surface effector mechanisms such as agglutination, neutralizing or opsonization of the microorganisms for phagocytosis are initiated. SP-A and SP-D stimulate chemotaxis of phagocytes and once bound to the phagocytes, the production of oxygen radicals can be induced. In the case of MBL the opsonization can be further enhanced by complement activation via the MBLectin pathway while conglutinin interacts with the complement system by binding to the complement degradation product iC3b. A number of receptors and binding molecules interacting with the collectins are found on the membrane or in association with the membrane of various cells responsible for phagocytosis and clearance of microorganisms. This paper focus on the structural aspects of the collectins and the receptors for collectins.