Molecular analysis of the bovine anaphylatoxin C5a receptor

Expression of FcμR by bovine mononuclear blood leukocytes

The receptor for IgM has been identified a few years ago, but its expression by bovine mononuclear cells has not yet been studied. We used rabbit antibodies against bovine FcμR to begin to fill this gap. Anti-FcμR antibodies bound to B lymphocytes and monocytes, although less than to neutrophils. Nonclassical and intermediate monocytes (CD172apos CD16pos) bound nonspecifically to rabbit antibodies, complicating analysis, but they bound more anti-FcμR antibodies than control antibodies, indicating that they also express the FcμR. They also express more C5a receptors than classical monocytes. Anti-FcμR antibodies did not bind to CD3pos αβT lymphocytes (both CD4pos and CD8pos) and γδT cells. At low temperature but not at physiological temperature, purified bovine IgM bound to all monocytes and strongly to all B cells, but hardly to CD3pos T cells. Monocytes and B cells bound human IgA, but IgA did not compete, whereas unlabeled bovine IgM competed for binding of labeled IgM. This supports the role of the FcμR, and not the FαμR, in IgM binding. Finally, we showed that monocytes were able to ingest bacteria opsonized with serum deprived of IgG, indicating their ability to perform IgM-dependent phagocytosis. In conclusion, surface expression of FcμR by unstimulated blood leukocytes was demonstrated on B cells and monocytes, but not on T cells.

Expression of the receptor for IgM (FcμR) by bovine neutrophils

Bovine neutrophils possess a particular set of receptors for immunoglobulins. They have been shown to express a distinctive receptor for IgG2, and it has long been known that they interact poorly with IgG1 but that they can use IgM antibodies as opsonins. We show that the binding of labeled IgM was inhibited by unlabeled IgM but not by IgA, suggesting that bovine neutrophils express a specific IgM receptor. The binding of non-aggregated IgM is strong at 4 °C, but shedding occurs at 37 °C. We designed anti-peptide antibodies based on the sequence of the FcμR, the newly described receptor for IgM. These antibodies bound to bovine neutrophils at 4 °C. At 37 °C, labeling was lost, but the loss was inhibited by pretreatment with cytochalasin D, indicating internalization of the receptor after cross-linking by antibodies. Neutrophils that had internalized the receptor were no longer able to bind IgM. Eosinophils showed a low level of FcμR expression. FcμR expression by neutrophils was not increased by stimulation with Toll-like receptor agonists or the complement anaphylatoxin C5a, and decreased by TNF-α. Exposure of neutrophils to IFN-γ for 18 h increased FcμR expression without augmenting the binding of IgG1 or IgG2. We confirmed that bovine neutrophils can use IgM to phagocytose and kill bacteria without the help of Complement. Neutrophils that have migrated into the lumen of inflamed lactating mammary glands expressed the FcμR. These results indicate that bovine neutrophils express an IgM receptor, the FcμR, which is functional to contribute to the opsonophagocytosis of bacteria at inflammatory sites. Expression of the FcμR by neutrophils gives IgM a particular importance for the immune defense in the bovine species.

Immune defences of the mammary gland in dairy ruminants

The mammary gland (MG) of ruminants is essential for assuring the immune protection and nutrition of the suckling youngs. The domestication of these species aimed at increasing milk production for human consumption enhanced udder susceptibility to infections and in this context, a better understanding of the MG immune defences has become a cornerstone for the success of dairy farming. In this review, we explore constitutive and inducible immune mechanisms of the mammary gland and briefly discuss the knowledge gaps that remain to be elucidated for the implementation of strategies focused on boosting mammary immune responses.

A Fixed Cohort Field Study of Gene Expression in Circulating Leukocytes From Dairy Cows With and Without Mastitis

Specifically designed gene expression studies can be used to prioritize candidate genes and identify novel biomarkers affecting resilience against mastitis and other diseases in dairy cattle. The primary goal of this study was to assess whether specific peripheral leukocyte genes expressed differentially in a previous study of dairy cattle with postpartum disease, also would be expressed differentially in peripheral leukocytes from a diverse set of different dairy cattle with moderate to severe clinical mastitis. Four genes were selected for this study due to their differential expression in a previous transcriptomic analysis of circulating leukocytes from dairy cows with and without evidence of early postpartum disease. An additional 15 genes were included based on their cellular, immunologic, and inflammatory functions associated with resistance and tolerance to mastitis. This fixed cohort study was conducted on a conventional dairy in Washington state. Cows >50 days in milk (DIM) with mastitis (n = 12) were enrolled along with healthy cows (n = 8) selected to match the DIM and lactation numbers of mastitic cows. Blood was collected for a complete blood count (CBC), serum biochemistry, leukocyte isolation, and RNA extraction on the day of enrollment and twice more at 6 to 8-days intervals. Latent class analysis was performed to discriminate healthy vs. mastitic cows and to describe disease resolution. RNA samples were processed by the Primate Diagnostic Services Laboratory (University of Washington, Seattle, WA). Gene expression analysis was performed using the Nanostring System (Nanostring Technologies, Seattle, Washington, USA). Of the four genes (C5AR1, CATHL6, LCN2, and PGLYRP1) with evidence of upregulation in cows with mastitis, three of those genes (CATHL6, LCN2, and PGLYRP1) were investigated due to their previously identified association with postpartum disease. These genes are responsible for immunomodulatory molecules that selectively enhance or alter host innate immune defense mechanisms and modulate pathogen-induced inflammatory responses. Although further research is warranted to explain their functional mechanisms and bioactivity in cattle, our findings suggest that these conserved elements of innate immunity have the potential to bridge disease states and target tissues in diverse dairy populations.

Bovine neutrophils in health and disease

Bovine neutrophils have similarities to those of other species with respect to mechanisms of their activation and migration into tissue, modulation of immune responses and the balance between microbial killing and host tissue damage. However, bovine neutrophils have biochemical and functional differences from those of other species, which may yield insights about the comparative biology of neutrophils. Neutrophils play protective and harmful roles in the infectious diseases of cattle that occur at times of transition: respiratory disease in beef calves recently arrived to feedlots and mastitis and other diseases of postparturient dairy cows. An important research focus is the mechanisms by which risk factors for these diseases affect neutrophil function and thereby lead to disease and the prospect of genetic or pharmacologic improvement of disease resistance. Further, in keeping with the One Health paradigm, cattle can be considered a model for studying the role of neutrophils in naturally occurring diseases caused by host-adapted pathogens and are thus an intermediary between studies of mouse models and investigations of human disease. Finally, the study of bovine neutrophils is important for agriculture, to understand the pathogenesis of these production-limiting diseases and to develop novel methods of disease prevention that improve animal health and reduce the reliance on antimicrobial use.

Local immunization impacts the response of dairy cows to Escherichia coli mastitis

Current vaccines to Escherichia coli mastitis have shown some albeit limited efficacy. Their mode of action has not been documented, and immune responses protecting the mammary gland against E. coli are not completely understood. To improve our knowledge of mammary gland immune protection, cows immunized either intramuscularly or intramammarily with the E. coli P4 were submitted to a homologous mastitis challenge. A third group of mock-immunized cows serve as challenge controls. Local immunization modified favorably the course of infection, by improving bacterial clearance while limiting inflammation. Systemic clinical signs and reduction in milk secretion were also contained. This occurred with a modification of the cytokine profile, such as an increase in IFN-γ and a reduction in TNF-α concentrations in milk. Concentrations of IL-17A and IL-22 increased in milk at the onset of the inflammatory response and remained high up to the elimination of bacteria, but concentrations did not differ between groups. Accelerated bacteriological cure was not linked to an increase in the initial efficiency of phagocytosis in milk. Results support the idea that antibodies did not play a major role in the improvement, and that cell-mediated immunity is the key to understanding E. coli vaccine-induced protection of the mammary gland.

Immunity to Bovine Herpesvirus 1: I. Viral lifecycle and innate immunity

Bovine herpesvirus 1 (BHV-1) causes a variety of diseases and is globally distributed. It infects via mucosal epithelium, leading to rapid lytic replication and latent infection, primarily in sensory ganglia. Large amounts of virus can be excreted by the host on primary infection or upon recrudescence of latent infection, resulting in disease spread. The bovine immune response to BHV-1 is rapid, robust, balanced, and long-lasting. The innate immune system is the first to respond to the infection, with type I interferons (IFNs), inflammatory cytokines, killing of infected host cells, and priming of a balanced adaptive immune response. The virus possesses a variety of immune evasion strategies, including inhibition of type I IFN production, chemokine and complement binding, infection of macrophages and neutrophils, and latency. BHV-1 immune suppression contributes to the severity of its disease manifestations and to the bovine respiratory disease complex, the leading cause of cattle death loss in the USA.

Microfluidic high-throughput RT-qPCR measurements of the immune response of primary bovine mammary epithelial cells cultured from milk to mastitis pathogens

Bovine mastitis, the inflammation of the udder, is a major problem for the dairy industry and for the welfare of the animals. To better understand this disease, and to implement two special techniques for studying mammary gland immunity in vitro, we measured the innate immune response of primary bovine mammary epithelial cells (pbMEC) from six Brown Swiss cows after stimulation with the heat-inactivated mastitis pathogens, Escherichia coli 1303 and Staphylococcus aureus 1027. The cells were extracted and cultivated from milk instead of udder tissue, which is usually done. The advantages of this technique are non-invasiveness and less contamination by fibroblasts. For the first time, pbMEC gene expression (GE) was measured with a microfluidic high-throughput real-time reverse transcription-quantitative PCR platform, the BioMark HD™ system from Fluidigm. In addition to the physiological analysis, the precision and suitability of this method was evaluated in a large data set. The mean coefficient of variance (± s.e.) between repeated chips was 4.3 ± 0.4% for highly expressed and 3.3 ± 0.4% for lowly expressed genes. Quantitative PCR (qPCR) replicate deviations were smaller than the cell culture replicate deviations, indicating that biological and cell culture differences could be distinguished from the background noise. Twenty-two genes (complement system, chemokines, inflammatory cytokines, antimicrobial peptides, acute phase response and toll-like receptor signalling) were differentially expressed (P < 0.05) with E. coli. The most upregulated gene was the acute phase protein serum amyloid A3 with 618-time fold. S. aureus slightly induced CCL5, IL10, TLR4 and S100A12 expression and failed to elicit a distinct overall innate immune response. We showed that, with this milk-derived pbMEC culture and the high-throughput qPCR technique, it is possible to obtain similar results in pbMEC expression as with conventional PCR and with satisfactory precision so that it can be applied in future GE studies in pbMEC.

Compromised neutrophil function and bovine E. coli mastitis: is C5a the missing link?

During early lactation, dairy cow are prone to developing severe mastitis in responses to intramammary Escherichia coli infections. These severe inflammatory responses have been correlated with reduced neutrophil function during the periparturient period. However, the causative mechanism of neutrophil dysfunction has not been elucidated. Studies in murine sepsis models have shown that during sepsis neutrophils are functionally paralysed due to the presence of high concentrations of complement factor 5a (C5a). In this review, we hypothesize that C5a as a critical early mediator in the development of severe E. coli mastitis. Furthermore, preliminary data suggest that crosstalk between C5a and TLR4 signalling in neutrophils may provide a positive feedback mechanism that may be involved in the pathogenesis of a severe mastitis response. Finally, we focus on the therapeutic potential of disrupting the C5a signalling pathway as an important strategy for treatment of severe E. coli mastitis in dairy cattle.

Consequences of interference of milk with chemoattractants for enzyme-linked immunosorbent assay quantifications

Concentrations of the chemoattractants CXCL1, CXCL2, CXCL3, CXCL8, and C5a in milk were reduced by the preparation of milk whey by high-speed centrifugation or with rennet. About half of the chemoattractants (35 to 65%) were associated with the casein micelle sediment, except when whey was prepared by acidification. Consequently, quantification of chemoattractants should be carried out preferentially with skimmed milk samples or, whenever whey is needed, with acidic whey samples. The interference of milk or milk whey with the enzyme-linked immunosorbent assays (ELISAs) used to quantify the chemoattractants was moderate, as long as tetramethylbenzidine (TMB), not ABTS [2,2'-azino-bis-(3-ethylbenzthiazoline-sulfonate)], was used as the substrate of peroxidase. These considerations will help to assess more precisely a component of the immune response of the mammary gland to infection.