Molecular Characterization of a Saposin-Like Protein Family Member Isolated from Bovine Lymphocytes

Synthetic bovine NK-lysin-derived peptide (bNK2A) does not require intra-chain disulfide bonds for bactericidal activity

Bovine NK-lysins are cationic antimicrobial proteins found predominantly in the cytosolic granules of T lymphocytes and NK-cells. NK-lysin-derived peptides show antimicrobial activity against both Gram positive and Gram negative bacteria. Mature NK-lysin protein has six well-conserved cysteine residues. This study was performed to assess whether synthetic bovine NK-lysin-derived peptide (bNK2A) forms disulfide bonds and whether disulfide bonds were essential for bNK2A antimicrobial activity. Two 30-mer bNK2A peptides were synthesized: one with two original cysteines and an analog with cysteines substituted with two serines. Mass spectrometry revealed lack of disulfide bonds in original peptide while CD spectrophotometry showed both peptides have similar α-helical structures. Since both peptides were equally inhibitory to Histophilus somni, disulfide bonds appeared dispensable for synthetic bNK2A peptide antibacterial activity.

The Immunology of Mammary Gland of Dairy Ruminants between Healthy and Inflammatory Conditions

The health of dairy animals, particularly the milk-producing mammary glands, is essential to the dairy industry because of the crucial hygienic and economic aspects of ensuring production of high quality milk. Due to its high prevalence, mastitis is considered the most important threat to dairy industry, due to its impacts on animal health and milk production and thus on economic benefits. The MG is protected by several defence mechanisms that prevent microbial penetration and surveillance. However, several factors can attenuate the host immune response (IR), and the possession of various virulence and resistance factors by different mastitis-causing microorganisms greatly limits immune defences and promotes establishment of intramammary infections (IMIs). A comprehensive understanding of MG immunity in both healthy and inflammatory conditions will be an important key to understand the nature of IMIs caused by specific pathogens and greatly contributes to the development of effective control methods and appropriate detection techniques. Consequently, this review aims to provide a detailed overview of antimicrobial defences in the MG under healthy and inflammatory conditions. In this sense, we will focus on pathogen-dependent variations in IRs mounted by the host during IMI and discuss the potential ramifications of these variations.

Parasiticidal activity of a novel synthetic peptide from the core α-helical region of NK-lysin

NK-lysin is an anti-microbial peptide that plays a critical role in innate immunity against infectious pathogens through its selective membrane disruptive property. We previously expressed and purified a full-length chicken NK-lysin (cNKL) recombinant protein, and demonstrated its in vitro anti-parasitic activity against the apicomplexan protozoan, Eimeria, the etiologic agent of avian coccidiosis. This study evaluated the in vitro and in vivo anti-parasitic properties of a synthetic peptide (cNK-2) incorporating a predicted membrane-permeating, amphipathic α-helix of the full-length cNKL protein. The cNK-2 peptide exhibited dose- and time-dependent in vitro cytotoxic activity against E. acervulina and E. tenella sporozoites. The cytotoxic activity of 1.5 μM of cNK-2 peptide against E. acervulina following 6h incubation was equal to that of 2.5 μM of melittin, the principal active component of apitoxin (bee venom) that also exhibits anti-microbial activity. Even greater activity was detected against E. tenella, where 0.3 μM of cNK-2 peptide was equivalent to 2.5 μM of melittin. Against Neospora caninum tacyzoites, however, the cytotoxic activity of cNK-2 peptide was inferior to that of melittin. Transmission electron microscopy of peptide-treated E. tenella sporozoites revealed disruption of the outer plasma membrane and loss of intracellular contents. In vivo administration of 1.5 μM of cNK-2 peptide increased protection against experimental E. acervulina infection, as measured by greater body weight gain and reduced fecal oocyst shedding, compared with saline controls. These results suggest that the cNK-2 synthetic peptide is a novel anti-infective peptide that can be used for protection against avian coccidiosis during commercial poultry production.

Characterization and localization of saposin-like protein-2 (SAP-2) in Fasciola gigantica

Fasciola gigantica saposin-like protein-2 (FgSAP-2) belongs to a family of lipid-interacting proteins that are involved in the cytolysis of target cells. In this study, we have cloned and expressed FgSAP-2 and produced the antibody against this recombinant protein. Rabbit antiserum against rFgSAP-2 reacted with a similar native protein in the whole body extracts of the 4-week-old juvenile and adult stage, as well as a protein in their excretion-secretion, but not in the tegument. In situ hybridization and immunofluorescence detection revealed the presence of SAP-2 mRNA transcripts and proteins in the cecal epithelial cells of 4-week-old juvenile and adult parasites, but not in the metacercariae and newly excysted juveniles. Moreover, SAP-2 is present only in the cecal epithelial cells lining the distal part of the digestive tract, but not in the tegumental-type epithelium lining the proximal part of the digestive tract. The rFgSAP-2 reacted with antisera from rabbits infected with F. gigantica metacercariae collected at 5 weeks, but not at 2 weeks after infection. Anti-rFgSAP-2 did not exhibit any cross-reactivity with the other parasites' antigens, including Opisthorchis viverrini, Eurytrema pancreaticum, Cotylophoron cotylophorum, Fischoederius cobboldi, Gigantocotyle explanatum, Paramphistomum cervi, Setaria labiato-papillosa, and Haemonchus placei. This finding indicated that SAP-2 is a unique protein that is expressed only in late juvenile and adult F. gigantica, and it could be considered for immunodiagnostic and as a vaccine candidate for fasciolosis.

Vaccines against bovine mastitis in the New Zealand context: what is the best way forward?

Mastitis is an important animal health disease which constitutes a serious problem for the dairy industry in New Zealand. Mastitis reduces milk yield and quality, necessitates the use of antibiotic therapy, with associated risks of contaminating the raw milk supply, and imposes a serious economic burden, currently estimated at NZ$300 million per year. Mastitis is caused by a variety of infectious agents. In the New Zealand context, with cattle grazing on pasture, Streptococcus uberis is a major bacterial pathogen, responsible for a significant proportion of clinical cases, especially during early lactation and the dry period. Other pathogens of significance include Staphylococcus aureus, Streptococcus dysgalactiae and Escherichia coli, as well as so-called 'minor pathogens', namely coagulase-negative staphylococci(CNS). Current strategies aimed at reducing cases of mastitis include improved hygiene in the farm environment, particularly with regards to the health and cleanliness of teats. Once mastitis occurs, antibiotic therapy is a favoured option, and as a prophylactic tool, in the form of dry-cow therapy, has also shown value. Prevention of mastitis using immunological tools such as vaccines lags behind the major vaccine breakthroughs that have been achieved in preventing and/or reducing the severity of numerous infectious diseases in animals. In this review, the current state of research in the area of development of vaccines against mastitis is summarised, with particular emphasis on bacteria important to the dairy farming industry in New Zealand. Few, if any, effective vaccines have been designed to prevent or mitigate intramammary infections. It is argued that novel approaches must be considered to search for vaccine candidates, and vaccines need to be designed and constructed within the special framework of their uses, in the mammary gland which offers a unique immunological environment. In addition, effective vaccines against mastitis due to Strep. uberis may be more likely to emerge from strategies that target the cell-mediated arm of the immune response rather than strategies that target specific antibody responses.

The role of dietary selenium in bovine mammary gland health and immune function

Mastitis is not only a major cause of economic losses to the dairy industry but also a major problem in ensuring the quality and safety of the milk, associated with high somatic cell counts and residues of antibiotics used for treatment. One innovative approach to protection against mastitis is to stimulate the animal's natural defense mechanisms. Technological advances in immunological research have increased our ability to exploit the immunity of the bovine mammary gland during periods of high susceptibility to disease. The trace element selenium affects the innate and the adaptive immune responses of the mammary gland through cellular and humoral activities. Substantial research has been carried out on the effect of selenium (Se) on the immune function of the mammary gland and subsequent improvement in bovine udder health and mastitis control. Levels higher than current recommendations and Se-yeast can potentially be used to enhance our capacity to modulate the physiological mechanisms of the bovine mammary gland to respond to infection. This article provides an overview of the most recent research in this field.

Bovine CD2-/NKp46+ cells are fully functional natural killer cells with a high activation status

BACKGROUND

Natural killer (NK) cells in the cow have been elusive due to the lack of specific NK cell markers, and various criteria including a CD3-/CD2+ phenotype have been used to identify such cells. The recent characterization of the NK-specific NKp46 receptor has allowed a more precise definition of bovine NK cells. NK cells are known as a heterogeneous cell group, and we here report the first functional study of bovine NK cell subsets, based on the expression of CD2.

RESULTS

Bovine CD2- NK cells, a minor subset in blood, proliferated more rapidly in the presence of IL-2, dominating the cultures after a few days. Grown separately with IL-2, CD2- and CD2+ NK cell subsets did not change CD2 expression for at least two weeks. In blood, CD2- NK cells showed a higher expression of CD44 and CD25, consistent with a high activation status. A higher proportion of CD2- NK cells had intracellular interferon-gamma in the cytoplasm in response to IL-2 and IL-12 stimulation, and the CD2- subset secreted more interferon-gamma when cultured separately. Cytotoxic capacity was similar in both subsets, and both carried transcripts for the NK cell receptors KIR, CD16, CD94 and KLRJ. Ligation by one out of two tested anti-CD2 monoclonal antibodies could trigger interferon-gamma production from NK cells, but neither of them could alter cytotoxicity.

CONCLUSION

These results provide evidence that bovine CD2- as well as CD2+ cells of the NKp46+ phenotype are fully functional NK cells, the CD2- subset showing signs of being more activated in the circulation.

Innate immunity of the bovine mammary gland

Understanding the immune defenses of the mammary gland is instrumental in devising and developing measures to control mastitis, the major illness of dairy ruminants. Innate immunity is an extremely broad field for investigation, and despite decades of research, our present knowledge of the innate defenses of the udder is incomplete. Yet, information is being gained on the recognition of pathogens by the mammary gland, and on several locally inducible defenses. The contribution of mammary epithelial cells to local defenses and to the mobilization of leucocytes is under growing scrutiny. Interactions of mastitis-causing bacteria such as Escherichia coli or Staphylococcus aureus and the mammary gland represents a suitable model for studies on innate immunity at an epithelium frontier. Powerful new research tools are radically modifying the prospects for the understanding of the interplay between the mammary gland innate defenses and mastitis-causing bacteria: genetic dissection of the immune response, microarray gene technology, transcriptomic methodologies and gene silencing by RNA interference will make possible the discovery of several of the key defense mechanisms which govern the susceptibility/resistance to mastitis at the molecular and genetic levels. It should then be possible to enhance the resistance of dairy ruminants to mastitis through immunomodulation and genetic improvement.