Bovine WC1(-) gammadeltaT cells incubated with IL-15 express the natural cytotoxicity receptor CD335 (NKp46) and produce IFN-gamma in response to exogenous IL-12 and IL-18

Development of a bead-based multiplex assay to quantify bovine interleukin-10, tumor necrosis factor-α, and interferon-γ concentrations in plasma and cell culture supernatant

The quantification of cytokines can improve our understanding of immune response and inflammation dynamics in dairy cows. Bead-based assays provide a sensitive, high-throughput platform, allowing for simultaneous quantification of multiple cytokines within a wide linear detection range. Our objective was to develop a multiplex bead-based assay using monoclonal antibodies for simultaneous quantification of bovine tumor necrosis factor (TNF)-α, IL-10, and IFN-γ in plasma and peripheral blood mononuclear cell (PBMC) culture supernatants. Recombinant cytokine standards produced in mammalian cells were used to determine the lower limit of detection and the linear detection range for each cytokine. The lower limit of detection was 110 pg/mL for IL-10, 95 pg/mL for TNF-α, and 20 pg/mL for IFN-γ. The linear quantification range was 110 to 241,000 pg/mL for IL-10, 95 to 620,000 pg/mL for TNF-α, and 20 to 130,000 pg/mL for IFN-γ. All 3 monoclonal capture and detection antibodies were specific for their respective cytokine analyte when using the recombinant IL-10, TNF-α, and IFN-γ standards. Intraassay and interassay coefficients of variation (CV) were <10% and <12%, respectively, for all analytes and samples matrices. Next, concentrations of native cytokines were determined in PBMC culture supernatants (n = 4) and in plasma from whole-blood samples (n = 6) with or without stimulation with Escherichia coli lipopolysaccharide or a mix of phorbol myristate acetate (PMA) and ionomycin. Peak concentrations of all 3 cytokines were secreted from PBMC after PMA/ionomycin stimulation (TNF-α, 8 h, range: 39,266-506,422 pg/mL; IL-10, 18 h, range: 15,770-63,415 pg/mL; IFN-γ 18 h, range: 189,977-492,659 pg/mL). In contrast, the highest concentrations in plasma from whole-blood stimulation were observed for IL-10 and TNF-α after LPS stimulation (TNF-α, 4 h, range: 1,764-13,460 pg/mL; IL-10, 24 h, range: 2,401-6,371 pg/mL), whereas PMA and ionomycin induced the highest secretion of IFN-γ (18 h, range: 53-20,215 pg/mL). In conclusion, the multiplex assay can quantify native IL-10, TNF-α, and IFN-γ across a broad concentration range in bovine plasma and cell culture supernatant, thereby providing a novel tool to evaluate inflammatory profiles in cattle and especially in dairy cows with inflammatory conditions. The existing multiplex assay can be expanded in the future by adding bead assays for additional bovine cytokines.

Harnessing Mycobacterium bovis BCG Trained Immunity to Control Human and Bovine Babesiosis

Babesiosis is a disease caused by tickborne hemoprotozoan apicomplexan parasites of the genus Babesia that negatively impacts public health and food security worldwide. Development of effective and sustainable vaccines against babesiosis is currently hindered in part by the absence of definitive host correlates of protection. Despite that, studies in Babesia microti and Babesia bovis, major causative agents of human and bovine babesiosis, respectively, suggest that early activation of innate immune responses is crucial for vertebrates to survive acute infection. Trained immunity (TI) is defined as the development of memory in vertebrate innate immune cells, allowing more efficient responses to subsequent specific and non-specific challenges. Considering that Mycobacterium bovis bacillus Calmette-Guerin (BCG), a widely used anti-tuberculosis attenuated vaccine, induces strong TI pro-inflammatory responses, we hypothesize that BCG TI may protect vertebrates against acute babesiosis. This premise is supported by early investigations demonstrating that BCG inoculation protects mice against experimental B. microti infection and recent observations that BCG vaccination decreases the severity of malaria in children infected with Plasmodium falciparum, a Babesia-related parasite. We also discuss the potential use of TI in conjunction with recombinant BCG vaccines expressing Babesia immunogens. In conclusion, by concentrating on human and bovine babesiosis, herein we intend to raise awareness of BCG TI as a strategy to efficiently control Babesia infection.

The Activating Receptors of Natural Killer Cells and Their Inter-Switching Potentials

The global incidence of cancer is on the increase and researchers are prospecting for specific and non-selective therapies derived from the immune system. The killer activating receptors of NK cells are known to be involved in immunosurveillance against tumor and virally-infected cells. These receptors belong to two main categories, namely the immunoglobulin like and C-lectin like families. Though they have different signal pathways, all the killer activating receptors have similar effector functions which include direct cytotoxicity and the release of inflammatory cytokines such as IFN-gamma and TNF-alpha. To transduce signals that exceed the activation threshold for cytotoxicity, most of these receptors require synergistic effort. This review profiles 21 receptors: 13 immunoglobulin-like, 5 lectin-like, and 3 others. It critically explores their structural uniqueness, role in disease, respective transduction signal pathways and their status as current and prospective targets for cancer immunotherapy. While the native ligands of most of these receptors are known, much work is required to prospect for specific antibodies, peptides and multi-target small molecules with high binding affinities.

Adoptive cell therapy of patient-derived renal cell carcinoma xenograft model with IL-15-induced γδT cells

Adoptive transfer of γδ T cells is an attractive approach for cell-based immunotherapy in treatment of renal cell carcinoma (RCC). Interleukin-15 (IL-15) is the key physiological cytokine that regulates γδ T cell differentiation, proliferation and survival. In this work, we determined that IL-15 have the capacity to enhance the anti-tumoral functions of γδ T cells. IL-15 can induce the upregulation of cytotoxicity-associated molecules on the γδ T cell surface, incite γδ T cell proliferation and decrease apoptosis. Moreover, the enhanced cytotoxicity of IL-15-induced γδ T cell was dependent on the interaction of NKG2D and MICA. Most importantly, we found that IL-15-induced γδ T cells effectively suppressed the tumor growth in vivo and prolonged the survival time of RCC-bearing patient‑derived xenograft (PDX) mice. These results are important for the prospective use of γδ T cells in clinical practice when designing novel cell-based immunotherapies against RCC.

Changes in the Molecular and Functional Phenotype of Bovine Monocytes during Theileria parva Infection

Theileria parva is the causative agent of East Coast fever (ECF), a tick-borne disease that kills over a million cattle each year in sub-Saharan Africa. Immune protection against T. parva involves a CD8⁺ cytotoxic T cell response to parasite-infected cells. However, there is currently a paucity of knowledge regarding the role played by innate immune cells in ECF pathogenesis and T. parva control.

Theileria parva is the causative agent of East Coast fever (ECF), a tick-borne disease that kills over a million cattle each year in sub-Saharan Africa. Immune protection against T. parva involves a CD8⁺ cytotoxic T cell response to parasite-infected cells. However, there is currently a paucity of knowledge regarding the role played by innate immune cells in ECF pathogenesis and T. parva control. Here, we demonstrate an increase in intermediate monocytes (CD14⁺⁺ CD16⁺) with a concomitant decrease in the classical (CD14⁺⁺ CD16⁻) and nonclassical (CD14⁺ CD16⁺) subsets at 12 days postinfection (dpi) during lethal infection but not during nonlethal T. parva infection. Ex vivo analyses of monocytes demonstrated upregulation of interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) mRNA and increased nitric oxide production during T. parva lethal infection compared to nonlethal infection at 10 dpi. Interestingly, no significant differences in peripheral blood parasite loads were observed between lethally and nonlethally infected animals at 12 dpi. In vitro stimulation with T. parva schizont-infected cells or Escherichia coli lipopolysaccharide (LPS) resulted in significant upregulation of IL-1β production by monocytes from lethally infected cattle compared to those from nonlethally infected animals. Strikingly, monocytes from lethally infected animals produced significant amounts of IL-10 mRNA after stimulation with T. parva schizont-infected cells. In conclusion, we demonstrate that T. parva infection leads to alterations in the molecular and functional phenotypes of bovine monocytes. Importantly, since these changes primarily occur in lethal infection, they can serve as biomarkers for ECF progression and severity, thereby aiding in the standardization of protection assessment for T. parva candidate vaccines.

WC1+ and WC1neg γδ T lymphocytes in intestinal mucosa of healthy and Mycobacterium avium subspecies paratuberculosis-infected calves

Mucosal surfaces such as the gastrointestinal tract, and skin are the front line of host defence and immunity against many pathogens. Gamma delta (γδ) T lymphocytes preferentially localize to the mucosal surfaces in several species including cattle, and are thought to play crucial roles in immunosurveillance and host defence, particularly against mycobacteria. Many γδ T cells are present in young calves, which is the period when calves are thought to be initially exposed to Mycobacterium avium subspecies paratuberculosis (Map). The role of mucosal γδ T cells in cattle, especially during host-pathogen interactions during early pre-clinical phases of infectious disease remains unclear. The purposes of this study were to investigate and characterize WC1⁺ and WC1^neg γδ  T cell subsets in various segments of the gastrointestinal (GI) tract of young calves, and then to examine γδ  T cell subsets in the distal small intestine of calves after experimental intestinal Map infection by direct Peyer's patch inoculation. We show that in healthy calves, the relative proportion of γδ T cells is constant throughout the GI mucosa, though the ileum has significantly more γδ T cells. In the distal intestine, γδ T cells are mainly WC1^neg and primarily located within the lamina propria of the jejunum and ileum. In Map-infected intestine, there are higher numbers of γδ T cells in the lamina propria and a greater proportion of WC1⁺ cells within the epithelial layer compared to control calves. While WC1^neg γδ T cells preferentially localize to the distal small intestine of healthy calves, WC1⁺ γδ T cells are increased in the intestinal mucosa during Map infection, which is suggestive of effector cell function. Further, spectral microscopy and flow cytometry in tandem will lead to improved understanding of the functions of these cells during health and disease.

Molecular and Antigenic Properties of Mammalian Cell-Expressed Theileria parva Antigen Tp9

East Coast Fever (ECF), caused by the tick-borne apicomplexan parasite Theileria parva, is a leading cause of morbidity and mortality in cattle of sub-Saharan Africa. The infection and treatment method (ITM) is currently the only vaccine available to control T. parva. Although ITM elicits levels of protection, its widespread adoption is limited by costs, laborious production process, and antibiotic co-treatment requirement, necessitating the development of a more sustainable vaccine. To this end, efforts have been concentrated in the identification of new T. parva vaccine antigens and in the development of suitable platforms for antigen expression. In this study, we investigated the molecular and antigenic properties of T. parva antigen Tp9 expressed by mammalian cells. Data indicate that Tp9 contains a signal peptide that is weakly functional in mammalian cells. Thus, Tp9 secretion from mammalian cells increased 10-fold after the native signal peptide was replaced with the human tissue plasminogen activator signal peptide (tPA). Sera from all T. parva-immune cattle recognized this recombinant, secreted Tp9. Additionally, PBMC from ITM-immunized cattle produced significant (p < 0.05) amounts of IFNγ following ex vivo exposure to Tp9, but this response varied between cattle of different MHC class I and class II genotypes. In addition, depletion experiments demonstrated that IFNγ to Tp9 was primarily produced by CD4⁺ T cells. Molecular analysis demonstrated that Tp9 presents a signal peptide that is weakly functional in mammalian cells, suggesting that it remains within lymphocytes during infection. Tp9 secretion from mammalian cells was substantially increased when the tPA secretion signal sequence was substituted for the native secretion signal sequence. Using full-length, recombinant Tp9 secreted from mammalian cells, we demonstrated that T. parva-immune cattle develop both humoral and cellular immune responses to this antigen. Collectively, these results provide rationale for further evaluation of Tp9 as a component of a T. parva subunit vaccine.

Symposium review: Immunological detection of the bovine conceptus during early pregnancy

Infertility and subfertility reduce the economic viability of dairy production. Inflammation reduces conception rates in dairy cattle, but surprisingly little information exists about the populations and the functions of immune cells at the conceptus-maternal interface during the periattachment period in dairy cattle. Early pregnancy is accompanied by immune stimulation at insemination and conceptus secretion of IFN-τ, pregnancy-associated glycoproteins, prostaglandins, and other molecules whose effects on immune function during early pregnancy have not been determined. Our working hypothesis is that pregnancy induces changes in immune cell populations and functions that are biased toward immunological tolerance, tissue remodeling, and angiogenesis. This review summarizes current knowledge, starting with insemination and proceeding through early pregnancy, as this is the period of maximal embryo loss. Results indicated that early pregnancy is accompanied by a marked increase in the proportion of endometrial immune cells expressing markers for natural killer (CD335) cells and cytotoxic T cells (CD8) along with an increase in cells expressing major histocompatibility class II antigens (macrophages and dendritic cells). This is accompanied by increased abundance of mRNA for IL-15, a natural killer growth factor, and IL-10 in the endometrium during early pregnancy. Furthermore, expression of indoleamine 2,3 dioxygenase was 15-fold greater in pregnant compared with cyclic heifers at d 17, but then declined by d 20. This enzyme converts tryptophan to kynurenine, which alters immune function by creating a localized tryptophan deficiency and by activation of the aryl hydrocarbon receptor and induction of downstream tolerogenic mediators. Expression of the aryl hydrocarbon receptor is abundant in the bovine uterus, but its temporal and spatial regulation during early pregnancy have not been characterized. Pregnancy is also associated with increased expression of proteins known to inhibit immune activation, including programed cell death ligand-1 (CD274), lymphocyte activation gene-3 (CD223), and cytotoxic T-lymphocyte associated protein-4 (CD152). These molecules interact with receptors on antigen-presenting cells and induce lymphocyte tolerance. Current results support the hypothesis that early pregnancy signaling in dairy heifers involves changes in the proportions of immune cells in the endometrium as well as induction of molecules known to mediate tolerance. These changes are likely essential for uterine wall remodeling, placentation, and successful pregnancy.

Bovine peripheral blood WC1+ and WC1neg γδ T lymphocytes modulate monocyte-derived macrophage effector functions during in vitro Mycobacterium avium subspecies paratuberculosis infection

The importance of bovine γδ T lymphocytes during anti-mycobacterial immunity is recognized; however, the role of major subsets of γδ T lymphocytes (WC1⁺ and WC1^neg) in this process remains unclear. We investigated how WC1⁺ and WC1^neg γδ T lymphocyte subsets of calves modulate monocyte-derived macrophage (MDM) functions during Map infection in vitro. To achieve this, Map-infected or uninfected MDMs from young calves were co-cultured with autologous WC1⁺ or WC1^neg γδ T lymphocytes. Our data indicate that WC1⁺ and WC1^neg γδ T lymphocytes of young calves modulate effector functions of MDMs with respect to Map killing, CD11b and MHC-II expression. We observed differences in IFN-γ production and CD25 expression on γδ T lymphocyte subsets, as well as MDM expression of CD1b when in contact with WC1^neg γδ T lymphocytes.

Porcine CD3(+)NKp46(+) Lymphocytes Have NK-Cell Characteristics and Are Present in Increased Frequencies in the Lungs of Influenza-Infected Animals

The CD3⁻NKp46⁺ phenotype is frequently used for the identification of natural killer (NK) cells in various mammalian species. Recently, NKp46 expression was analyzed in more detail in swine. It could be shown that besides CD3⁻NKp46⁺ lymphocytes, a small but distinct population of CD3⁺NKp46⁺ cells exists. In this study, we report low frequencies of CD3⁺NKp46⁺ lymphocytes in blood, lymph nodes, and spleen, but increased frequencies in non-lymphatic organs, like liver and lung. Phenotypic analyses showed that the majority of CD3⁺NKp46⁺ cells coexpressed the CD8αβ heterodimer, while a minor subset expressed the TCR-γδ, which was associated with a CD8αα⁺ phenotype. Despite these T-cell associated receptors, the majority of CD3⁺NKp46⁺ lymphocytes displayed a NK-related phenotype (CD2⁺CD5⁻CD6⁻CD16⁺perforin⁺) and expressed mRNA of NKp30, NKp44, and NKG2D at similar levels as NK cells. Functional tests showed that CD3⁺NKp46⁺ lymphocytes produced IFN-γ and proliferated upon cytokine stimulation to a similar extent as NK cells, but did not respond to the T-cell mitogen, ConA. Likewise, CD3⁺NKp46⁺ cells killed K562 cells with an efficiency comparable to NK cells. Cross-linking of NKp46 and CD3 led to degranulation of CD3⁺NKp46⁺ cells, indicating functional signaling pathways for both receptors. Additionally, influenza A(H1N1)pdm09-infected pigs had reduced frequencies of CD3⁺NKp46⁺ lymphocytes in blood, but increased frequencies in the lung in the early phase of infection. Thus, CD3⁺NKp46⁺ cells appear to be involved in the early phase of influenza infections. In summary, we describe a lymphocyte population in swine with a mixed phenotype of NK and T cells, with results so far indicating that this cell population functionally resembles NK cells.

Characterization and expression of monoclonal antibody-defined molecules on resting and activated bovine αβ, γδ T and NK cells

Monoclonal antibodies (mAbs) specific for leukocyte differentiation molecules (LDMs) were developed during the past few decades to expand reagents for research in ruminants, pigs, and horses. The specificity of some of the mAb-defined molecules was determined through participation in international workshops. Other molecules identified with mAbs during this time, and more recently with mAbs developed after the workshops, have remained partially characterized. Efforts are now underway to characterize the specificity of these mAbs. As reported here, flow cytometry (FC) was used to screen two sets of hybridomas to determine how many of the hybridomas produce mAbs that detect molecules with up-regulated expression on activated lymphocytes or NK cells. Thirty four hybridomas were identified. Comparison of the patterns of reactivity of the mAbs showed some of the mAbs formed clusters that recognize 5 different molecules. FC showed one cluster recognized CD25. Use of mass spectrometry showed 4 clusters recognized orthologues of CD26, CD50, gp96 and signaling lymphocytic activation molecule family member 9 (SLAMF9). Verification and documentation that CD26, CD50, and SLAMF9 were only up-regulated on activated cells was obtained with PBMC from calves vaccinated with a Mycobacterium avium paratuberculosis mutant, Map-relA. CD26 and CD50 were up-regulated on NK cells, CD4 and CD8 T cells and γδ T cells. SLAMF9 was only up-regulated on CD4, CD8, and γδ T cells. gp96 was detected on granulocytes, monocytes and activated NK cells. Detection was attributable to the binding of gp96 to its receptor CD91.

IL-12 and IL-18 induce interferon-γ production and de novo CD2 expression in porcine γδ T cells

γδ T cells are highly abundant in the blood and spleen of pigs but little is known about their functional differentiation. In this study the potential of the type-1 polarizing cytokines IL-12 and IL-18 in combination with IL-2 and Concanavalin A (ConA) to stimulate porcine γδ T cells was investigated. Stimulation of purified γδ T cells with ConA and IL-2 induced a strong proliferation of CD2(-) γδ T cells, whereas additional stimulation with IL-12 and IL-18 caused a stronger proliferation of CD2(+) γδ T cells. IFN-γ could only be detected in supernatants of γδ T-cell cultures supplemented with IL-12 and IL-18. Experiments with sorted CD2/SWC5-defined γδ T-cell subsets revealed that CD2(+)SWC5(-) γδ T cells are the main producers of IFN-γ following stimulation with IL-2/IL-12/IL-18. Additional stimulation with ConA led to an upregulation of CD2 within the CD2(-) γδ T cell subsets, indicating a previously unnoticed plasticity of CD2-defined γδ T cell subsets.

NKp46+ CD3+ cells: a novel nonconventional T cell subset in cattle exhibiting both NK cell and T cell features

The NKp46 receptor demonstrates a high degree of lineage specificity, being expressed almost exclusively in NK cells. Previous studies have demonstrated NKp46 expression by T cells, but NKp46+ CD3+ cells are rare and almost universally associated with NKp46 acquisition by T cells following stimulation. In this study we demonstrate the existence of a population of NKp46+ CD3+ cells resident in normal bovine PBMCs that includes cells of both the αβ TCR+ and γδ TCR+ lineages and is present at a frequency of 0.1-1.7%. NKp46+ CD3+ cells express transcripts for a broad repertoire of both NKRs and TCRs and also the CD3ζ, DAP10, and FcεR1γ but not DAP12 adaptor proteins. In vitro functional analysis of NKp46+ CD3+ cells confirm that NKp46, CD16, and CD3 signaling pathways are all functionally competent and capable of mediating/redirecting cytolysis. However, only CD3 cross-ligation elicits IFN-γ release. NKp46+ CD3+ cells exhibit cytotoxic activity against autologous Theileria parva-infected cells in vitro, and during in vivo challenge with this parasite an expansion of NKp46+ CD3+ cells was observed in some animals, indicating the cells have the potential to act as an anti-pathogen effector population. The results in this study identify and describe a novel nonconventional NKp46+ CD3+ T cell subset that is phenotypically and functionally distinct from conventional NK and T cells. The ability to exploit both NKRs and TCRs suggests these cells may fill a functional niche at the interface of innate and adaptive immune responses.

Comparative biology of γδ T cell function in humans, mice, and domestic animals

γδ T cells are a functionally heterogeneous population and contribute to many early immune responses. The majority of their activity is described in humans and mice, but the immune systems of all jawed vertebrates include the γδ T cell lineage. Although some aspects of γδ T cells vary between species, critical roles in early immune responses are often conserved. Common features of γδ T cells include innate receptor expression, antigen presentation, cytotoxicity, and cytokine production. Herein we compare studies describing these conserved γδ T cell functions and other, potentially unique, functions. γδ T cells are well documented for their potential immunotherapeutic properties; however, these proposed therapies are often focused on human diseases and the mouse models thereof. This review consolidates some of these studies with those in other animals to provide a consensus for the current understanding of γδ T cell function across species.

Oenothein B, a cyclic dimeric ellagitannin isolated from Epilobium angustifolium, enhances IFNγ production by lymphocytes

Oenothein B is a polyphenol isolated from Epilobium angustifolium and other plant sources, which has been reported to exhibit immunomodulatory properties. Oenothein B is known to activate myeloid cells and induce the production of IL-1 and other cytokines. However, its effects on lymphocytes are unknown. In this report, we show that oenothein B stimulated innate lymphocytes, including bovine and human γδ T cells and NK cells, resulting in either increased CD25 and/or CD69 expression. We also demonstrate that oenothein B enhanced the production of interferon-γ (IFNγ) by bovine and human NK cells alone and in combination with interleukin-18 (IL-18), a response not observed with other commonly studied polyphenols. Furthermore, we demonstrate that oenothein B enhanced the production of IFNγ by human T cells. Since IFNγ contributes to antitumor, antibacterial, and antiviral cell responses, these data suggest an additional mechanism that could account, at least in part, for the immune enhancing properties of oenothein B.

Gamma-delta T-cell responses during subcutaneous Mycobacterium avium subspecies paratuberculosis challenge in sensitized or naive calves using matrix biopolymers

We have developed a model to explore the early immune response against Mycobacterium avium subspecies paratuberculosis (Map) infection in the bovine calf using subcutaneously placed liquid gel matrix biopolymer (matrigel) containing live Map. Matrigel rapidly polymerizes in vivo, retains recruited cellular infiltrates and soluble immune mediators, and can be rapidly removed 48 hours later and depolymerized for analysis. In this study, we examined early host immune events at matrigel/Map sites; recruited cells were evaluated by histopathology and flow cytometry, and cytokines were measured by flow cytometry, enzyme-linked immunosorbent assay, and Luminex bead immunoassay. Our results demonstrate earlier recruitment of gamma-delta (γδ) T cells to matrigel/Map challenge sites compared to CD4+ T cells. We also show that significantly more γδ T cells were recruited to matrigel/Map sites postinfection day 7 compared to postinfection day 30 and that these cells produced significant amounts of the cytokine interferon gamma. We also provide evidence that peripheral blood-derived γδ T-cell subsets in cattle differentially generate interferon gamma, suggesting distinct roles for these cells. These data provide unique insight into initial antimycobacterial host cellular immune responses following Map infection in calves.

Generation and characterization of monoclonal antibodies to equine NKp46

The immunoreceptor NKp46 is considered to be the most consistent marker of NK cells across mammalian species. Here, we use a recombinant NKp46 protein to generate a panel of monoclonal antibodies that recognize equine NKp46. The extracellular region of equine NKp46 was expressed with equine IL-4 as a recombinant fusion protein (rIL-4/NKp46) and used as an immunogen to generate mouse monoclonal antibodies (mAbs). MAbs were first screened by ELISA for an ability to recognize NKp46, but not IL-4, or the structurally related immunoreceptor CD16. Nine mAbs were selected and were shown to recognize full-length NKp46 expressed on the surface of transfected CHO cells as a GFP fusion protein. The mAbs recognized a population of lymphocytes by flow cytometric analysis that was morphologically similar to NKp46+ cells in humans and cattle. In a study using nine horses, representative mAb 4F2 labeled 0.8-2.1% PBL with a mean fluorescence intensity consistent with gene expression data. MAb 4F2+ PBL were enriched by magnetic cell sorting and were found to express higher levels of NKP46 mRNA than 4F2- cells by quantitative RT-PCR. CD3-depleted PBL from five horses contained a higher percentage of 4F2+ cells than unsorted PBL. Using ELISA, we determined that the nine mAbs recognize three different epitopes. These mAbs will be useful tools in better understanding the largely uncharacterized equine NK cell population.

Comparative gamma delta T cell immunology: a focus on mycobacterial disease in cattle

A theme among many pathogenic mycobacterial species affecting both humans and animals is a prolonged asymptomatic or latent period that can last years to decades. The mechanisms that favor progression to active disease are not well understood. Pathogen containment is often associated with an effective cell-mediated or T-helper 1 immune profile. With certain pathogenic mycobacteria, such as Mycobacterium avium subspecies paratuberculosis, a shift to active clinical disease is associated with loss of T-helper 1 immunity and development of an ineffective humoral or T-helper 2 immune response. Recently γδ T cells have been shown to play a role early in mycobacterial infections and have been hypothesized to influence disease outcome. The purpose of this paper is to compare recent advancements in our understanding of γδ T cells in humans, cattle, and mice and to discuss roles of γδ T cells in host response to mycobacterial infection.

The bovine spleen: interactions among splenic cell populations in the innate immunologic control of hemoparasitic infections

Over the past several years, innate immunity has been recognized as having an important role as a front-line defense mechanism and as an integral part of the adaptive immune response. Innate immunity in cattle exposed to hemoparasites is spleen-dependent and age-related. In this review, we discuss general aspects of innate immunity and the cells involved in this aspect of the response to infection. We also provide examples of specific splenic regulatory and effector mechanisms involved in the response to Babesia bovis, an important tick-borne hemoparasitic disease of cattle. Evidence for the regulatory and effector role of bovine splenic monocytes and DC both in directing a type-1 response through interaction with splenic NK cells and γδT-cells will be presented.

Identification of new populations of chicken natural killer (NK) cells

Natural killer (NK) cell activity is conserved throughout vertebrate development, but characterization of non-mammalian NK-cells has been hampered by the absence of specific mAbs for these cells. Monoclonal antibodies were generated against in vitro IL-2 expanded sorted CD3-CD8alpha+ peripheral blood lymphocytes, previously described to contain chicken NK-cells. Screening of embryonic and adult splenocytes with hybridoma supernatants resulted in five candidate NK markers. Activation of chicken NK-cells with PMA/Ionomycin or with the NK target cell-line LSCC-RP9 resulted in increased expression of CD107 (LAMP-1) and a newly developed flow cytometry based cytotoxicity assay showed that NK-cells were able to kill target cells. Combining NK markers with functional assays indicated that marker positive cells showed NK-cell function. In conclusion, we generated new monoclonal antibodies and developed two functional assays which will enhance our understanding of the role of NK-cells in healthy and diseased chickens.

Gamma-delta T cell subsets are differentially associated with granuloma development and organization in a bovine model of mycobacterial disease

The characteristic lesion in bovine tuberculosis is well-organized respiratory granulomas. This is typically associated with a strong T-helper 1 biased cell-mediated immune response and eventual containment of the infection. In bovine paratuberculosis, the classic lesion is unorganized granulomatous intestinal inflammation. Clinical paratuberculosis is associated with a T-helper 2 biased humoral immune response and eventual death because of inability of the host to contain the infection. Recent reports have suggested that gamma-delta (gammadelta) T cells play a significant role in granuloma development and/or maintenance during initial stages of infection and may influence the subsequent adaptive immune response. The objective of this study was to use an in vivo bovine model to evaluate gammadelta T cells during the early host immune response to mycobacterial infection. We used immunofluorescent staining, hyperspectral microscopy, and computerized assisted morphometry to evaluate staining and distribution of gammadelta T cells during development of organized and unorganized granulomas. Our data suggest that bovine gammadelta T cell subsets are differentially recruited to early infection sites, and may be instrumental during the initial antimycobacterial host immune response as well as for granuloma organization.

Bovine neonate natural killer cells are fully functional and highly responsive to interleukin-15 and to NKp46 receptor stimulation

Natural killer (NK) cells are key components of the innate immune system with their killing and cytokine producing abilities. Bovine NK cells have been characterized as NKp46⁺/CD3⁻ lymphocytes, but little is known about these cells in neonatal calves. As the newborn calf, with an insufficiently developed acquired immunity, has to employ the innate immune system, we wanted to investigate whether neonate NK cells had the same characteristics as cells from older calves. Freshly isolated neonate and calf NK cells presented the same resting CD2⁺/CD25^low/CD8^−/low phenotype. Neonates less than 8 days old had one third of the circulating NKp46⁺ cells of older calves, but the NK cells proliferated more actively in vitro in the presence of interleukin (IL)-2 or IL-15. Moreover, neonate NK cells were more cytotoxic both in an NKp46 mediated redirected lysis assay and in direct killing of a bovine cell line MDBK when cultured in the presence of IL-15. Neonate and calf NK cells cultured in the presence of IL-2 and then stimulated with IL-12 produced similar dose-dependent interferon (IFN)-γ amounts, while IL-15 cultured NK cells did not give such a response whatever the age. However, neonatal NK cells cultured in IL-15 and stimulated by IL-12 concomitantly with cross-linking of NKp46, produced 4 to 5 times more IFN-γ than calf NK cells. These data suggest that although present in lower number at birth, neonate NK cells are fully functional and are more responsive to IL-15 and activation through the NKp46 receptor than NK cells from older calves.

Bovine natural killer cells

Natural killer (NK) cells have received much attention due to their cytotoxic abilities, often with a focus on their implications for cancer and transplantation. But despite their name, NK cells are also potent producers of cytokines like interferon-gamma. Recent discoveries of their interplay with dendritic cells and T-cells have shown that NK cells participate significantly in the onset and shaping of adaptive cellular immune responses, and increasingly these cells have become associated with protection from viral, bacterial and parasitic infections. Furthermore, they are substantially present in the placenta, apparently participating in the establishment of normal pregnancy. Consequently, NK cells have entered arenas of particular relevance in veterinary immunology. Limited data still exist on these cells in domestic animal species, much due to the lack of specific markers. However, bovine NK cells can be identified as NKp46 (CD335) expressing, CD3(-) lymphocytes. Recent studies have indicated a role for NK cells in important infectious diseases of cattle, and identified important bovine NK receptor families, including multiple KIRs and a single Ly49. In this review we will briefly summarize the current understanding of general NK cell biology, and then present the knowledge obtained thus far in the bovine species.

Avian NK activities, cells and receptors

Natural killer (NK) activity has been examined in birds for over 30 years, but evidence that avian NK activity plays crucial roles in disease is only suggestive. In chickens, NK activity is mediated by TCR0 cells in the intestinal epithelium, but elsewhere subsets of alphabeta and gammadelta T cells (NKT cells) may be more important. There are few lectin-like NK receptor genes, located in the genomic region syntenic with the natural killer complex (NKC) as well as the major histocompatibility complex (MHC). In contrast, a huge number of Ig-like receptor genes are located in a region syntenic with the leukocyte receptor complex (LRC).