Analysis of immune responses directed toward a recombinant early secretory antigenic target six-kilodalton protein-culture filtrate protein 10 fusion protein in Mycobacterium bovis-infected cattle

Cell-mediated immune responses are critical for protective immunity to mycobacterial infections. Recent progress in defining mycobacterial antigens has determined that region of difference 1 (RD1) gene products induce strong T-cell responses, particularly the early secretory antigenic target 6-kDa (ESAT-6) protein and culture filtrate protein 10 (CFP10). However, comprehensive analysis of the immune response towards these antigens is incompletely characterized. To evaluate recall responses to ESAT-6 and CFP10, peripheral blood mononuclear cells from M. bovis-infected cattle were stimulated in vitro with a recombinant ESAT-6 (rESAT-6)-CFP10 fusion protein and compared to responses induced by M. bovis-derived purified protein derivative. Following antigenic stimulation, activation marker expression was evaluated. Significant proliferative responses (P < 0.05) were evident in CD4(+), CD8(+), immunoglobulin M-positive, and CD172a(+) cell fractions after 6 days of culture. Expression of CD25 and CD26 was increased (P < 0.05) on CD4(+), CD8(+), and gammadelta T-cell-receptor-positive cells. CD4(+) and CD8(+) cells also exhibited significant changes (P < 0.05) in expression of CD45 isoforms. Using a flow cytometry-based proliferation assay, it was determined that CD45R expression is downregulated (P < 0.05) and that CD45RO expression is upregulated (P < 0.05) on proliferating (i.e., activated) CD4(+) cells. Collectively, data indicate that recall immune responses directed toward the rESAT-6-CFP10 fusion protein or purified protein derivative are comparable and that recall to mycobacterial antigens correlates with a CD45RO(+) phenotype.

Bovine natural killer cells acquire cytotoxic/effector activity following activation with IL‐12/15 and reduce Mycobacterium bovis BCG in infected macrophages

Bovine natural killer (NK) cells were recently identified by positive selection of a NK cell-activating receptor p46 (NKp46)+ CD3- lymphocyte population, which expresses CD25 and CD8 and lyses tumor cell lines following stimulation with recombinant interleukin-2. In the current work, we characterize the cytotoxic/effector potential of a CD3(-)CD8(-)CD11b- population isolated through negative selection of bovine peripheral blood leukocytes. This population is CD25(lo)CD62(hi) when isolated and becomes CD25hiCD62L(lo) following cytokine stimulation. Activated bovine NK cells increase expression of granulysin, interferon-gamma, and perforin and have cytotoxic activity against human tumor cells and Mycobacterium bovis bacillus Calmette-Guerin-infected alveolar and monocyte-derived macrophages. Expression of a bovine homologue of the CD56 neural adhesion molecule expressed by human NK cells was detected in mRNA from brain tissue but was not detected in peripheral blood mononuclear cells or purified NK cell mRNA. Analysis of mRNA from nonstimulated peripheral blood NK cells demonstrates the constitutive expression of homologues of human NK receptors NKp46, CD244, and CD94 and the granule proteins granulysin and perforin. Phorbol ester-stimulated CD8+ T cells also expressed CD244 and CD94, and CD4+ T cells expressed CD94. These NK cell receptors bearing T lymphocytes may represent memory subsets characterized in humans. The results of these studies demonstrate that bovine NK cells may play an important role in the innate immune responses of cattle.

Use of recombinant ESAT-6:CFP-10 fusion protein for differentiation of infections of cattle by Mycobacterium bovis and by M. avium subsp. avium and M. avium subsp. paratuberculosis

Immunological diagnosis of Mycobacterium bovis infection of cattle is often confounded by cross-reactive responses resulting from exposure to other mycobacterial species, especially Mycobacterium avium. Early secretory antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10) are dominant gamma interferon (IFN-gamma)-inducing antigens of tuberculous mycobacteria, and they are absent from many environmental nontuberculous mycobacteria. Because M. avium exposure is the primary confounding factor in the diagnosis of M. bovis-infected animals, in vitro responses to a recombinant ESAT-6:CFP-10 (rESAT-6:CFP-10) fusion protein by blood leukocytes from cattle naturally exposed to M. avium or experimentally challenged with Mycobacterium avium subsp. avium or Mycobacterium avium subsp. paratuberculosis were compared to responses by M. bovis-infected cattle. Responses to heterogeneous mycobacterial antigens (i.e., purified protein derivatives [PPDs] and whole-cell sonicates [WCSs]) were also evaluated. Tumor necrosis factor alpha (TNF-alpha), IFN-gamma, and nitric oxide responses by M. bovis-infected cattle to rESAT-6:CFP-10 exceeded (P < 0.05) the corresponding responses by cattle naturally sensitized to M. avium. Experimental infection with M. bovis, M. avium, or M. avium subsp. paratuberculosis induced significant (P < 0.05) IFN-gamma and nitric oxide production to WCS and PPD antigens, regardless of the mycobacterial species used for the preparation of the antigen. Responses to homologous crude antigens generally exceeded responses to heterologous antigens. Nitric oxide and IFN-gamma responses to rESAT-6:CFP-10 by blood leukocytes from M. bovis-infected calves exceeded (P < 0.05) the corresponding responses of noninfected, M. avium-infected, and M. avium subsp. paratuberculosis-infected calves. Despite the reported potential for secretion of immunogenic ESAT-6 and CFP-10 proteins by M. avium and M. avium subsp. paratuberculosis, it appears that use of the rESAT-6:CFP-10 fusion protein will be useful for the detection of tuberculous cattle in herds with pre-existing sensitization to M. avium and/or M. avium subsp. paratuberculosis.

CD80 and CD86, but not CD154, augment DNA vaccine-induced protection in experimental bovine tuberculosis

DNA vaccination is known to elicit robust cellular and humoral responses to encoded antigen. The co-administration of costimulatory molecules CD80 (B7-1), CD86 (B7-2) and CD154 (CD40L) has been shown to enhance immune responses in several murine models. The role of specific costimulatory molecules in non-rodent species remains incompletely characterized. In these studies, we demonstrate that the co-administration of CD80 and CD86, but not CD154, to an existing candidate subunit DNA vaccine (ESAT-6) against bovine tuberculosis, enhances protection after aerosol challenge with virulent Mycobacterium bovis. Additionally, we have shown that vaccination with M. bovis BCG is protective against tuberculosis following aerosol challenge in cattle. Two independent trials were conducted in cattle to determine the adjuvant effect of encoded antigen + CD80/CD86 and directly compare the adjuvant activities of CD80/CD86 to those of CD154. Co-administration of either CD80/CD86 or CD154 enhanced ESAT-6-specific IFN-gamma responses as compared to animals vaccinated with ESAT-6 DNA alone. However, following aerosol challenge, only animals vaccinated with CD80/CD86 possessed decreased pathology of the lungs and associated lymph nodes, as measured by gross examination, radiographic lesion morphometry and bacterial recovery. Collectively, these results demonstrate that the co-administration of costimulatory molecules with a protective antigen target enhances bovine immune responses to DNA vaccination, and that CD80/CD86 is superior to CD154 in augmenting DNA vaccine-induced protection in experimental bovine tuberculosis.

Characterization of Bovine Homologues of Granulysin and NK-lysin

Granulysin and NK-lysin are antimicrobial proteins found in the granules of human and swine cytotoxic lymphocytes. A murine counterpart to granulysin has not been identified to date, indicating the importance of additional models to fully characterize the role of granulysin-like molecules in the immune response to infectious disease. Two partial nucleotide sequences corresponding to the complete functional domain of granulysin and NK-lysin were amplified from bovine PBMC mRNA. Following stimulation with phorbol ester and calcium ionophore, expression of the bovine gene was detected in CD3(+) T cells, CD4(+) T cells, CD8(+) T cells, WC1(+) gammadelta T cells, and PBMC depleted of CD3(+) T cells, but was absent in CD21(+) cells and CD14(+) cells. Intracellular flow cytometry and immunoblotting confirmed the presence of protein corresponding to the bovine granulysin homologue in activated T lymphocytes and PBMC. Synthetic human, bovine, and swine peptides corresponding to the C terminus of helix 2 through helix 3 region of granulysin displayed potent antimicrobial activity against Escherichia coli, Salmonella enteritidis, Staphylococcus aureus, and Mycobacterium bovis bacillus Calmette-Guérin. Human and bovine peptides corresponding to helix 2 displayed antimycobacterial activity against M. bovis bacillus Calmette-Guérin. Expression of the bovine gene was detected in laser microscopy-dissected lymph node lesions from an M. bovis-infected animal. The identification of a biologically active bovine homologue to granulysin demonstrates the potential of the bovine model in characterizing the role of granulysin in the immune response to a variety of infectious agents.

Comparison of the response of primary human blood monocytes and the U937 human monocytic cell line to two different sizes of alumina ceramic particles

It is well recognized that wear particles derived from orthopaedic implants have the potential to induce inflammation, which may eventually lead to aseptic loosening of the artificial joint. We hypothesized that alumina ceramic particles of different sizes cause a differential cytokine response by human monocytes. To test this hypothesis a human monocytic cell line (U937) and primary human blood monocytes obtained from healthy volunteers were exposed to ceramic particles within the range known to be generated in vivo. Cellular responses were measured by quantifying the relative gene expression of 12 different cytokines using TAQman Real-Time Polymerase Chain Reaction (RT-PCR). Our results demonstrate that at a particle to cell ratio of 100:1, 0.5 microm ceramic particles consistently provoked higher amounts of Interleukin-1alpha (IL-1alpha), IL-1beta, IL-8, IL-10 and Tumor necrosis factor-alpha (TNF-alpha) steady state mRNA by U937 cells. As expected, the variability of cytokine expression in primary blood monocytes was much higher compared to the cell line however, a similar trend was observed. These results show a differential response to ceramic particle size, which may imply that 0.5 microm particles are less biocompatible. New ceramic implants can be designed to generate a known particle size range in vivo. Implant materials of this type may induce relatively lower levels of production of inflammatory cytokines resulting in a reduced incidence of failure due to aseptic loosening.

Estrogen receptor-alpha deficiency promotes increased TNF-alpha secretion and bacterial killing by murine macrophages in response to microbial stimuli in vitro

In this series of studies, we determined the potential role of intracellular estrogen receptors (ER), ERalpha and ERbeta, on macrophage function in response to bacterial stimuli. The sex hormone 17beta-estradiol (E(2)) and ER have been shown to modulate inflammatory responses as well as T helper cell type 1 (TH1)/TH2 responses. The mechanisms E(2) and its receptors use to alter these immune functions remain largely unknown. ERalpha and ERbeta possess complex actions in tissues where they are expressed. We have characterized the receptor repertoire of murine dendritic cells and thioglycollate-elicited peritoneal macrophages (PM). Both cell types express mRNA for ERalpha. Neither cell type expressed detectable amounts of ERbeta mRNA, as determined by reverse transcriptase-polymerase chain reaction using exon-specific primers spanning each of the seven intron/exon junctions. Primary macrophages from ERalpha- and ERbeta-deficient severe combined immunodeficiency mice [ERalpha knockout (KO) and ERssKO, respectively] were used to delineate the effects and potential mechanisms via which steroid receptors modulate macrophage function. ERalpha-deficient PM exposed ex vivo to lipopolysaccharide or Mycobacterium avium exhibited significant increases in tumor necrosis factor alpha (TNF-alpha) secretion as well as reduction in bacterial load when compared with wild-type (WT) PM. In contrast, ERbeta-deficient PM possessed no significant difference in TNF-alpha secretion or in bacterial load when compared with WT littermates. These studies suggest that ERalpha, but not ERbeta, modulates murine PM function.

Effects of supplemental lactoferrin on serum lactoferrin and IgG concentrations and neutrophil oxidative metabolism in Holstein calves

Lactoferrin (LF) is an iron-binding protein present in both colostrum and secondary granules of polymorphonuclear neutrophils (PMNs). We hypothesized that supplemental LF enhances neutrophil function in neonatal calves. Newborn calves were assigned to receive colostrum (C), colostrum + LF (CLF, 1 g/kg), or milk replacer + LF (MRLF, 1 g/kg). Serum (LF and IgG) and whole blood (neutrophil isolation) samples were obtained prior to treatment (day 0) and at 24 hours and 9 days of age. Serum IgG concentrations (mean +/- SD) in C, CLF, and MRLF calves at 24 hours were 1,911 +/- 994 mg/dL, 2,181 +/- 625 mg/dL, and 0 mg/ dL, respectively. Serum LF concentrations in C, CLF, and MRLF calves on day 0 were 324 +/- 334 ng/mL (range 0-863 ng/mL), 135 +/- 158 ng/mL (range 0-429 ng/mL), and 318 +/- 337 ng/mL (range 0-964 ng/mL), respectively. LF concentrations in C, CLF, and MRLF calves at 24 hours were significantly higher (P < .05), at 1,564 +/- 1,114 ng/mL (range 335-3,628 ng/mL, 2,237 +/- 936 ng/mL (range 31-3,287 ng/mL), and 3,189 +/- 926 ng/mL (range 1,736-4,120 ng/mL), respectively. Cytochrome c reduction in opsonized zymosan-treated or phorbol ester-treated cells was not significantly affected by supplemental LF provided at birth. Oral LF is absorbed in calves but does not alter PMN superoxide production and does not alter IgG absorption.

Dietary soy phytoestrogens and ERalpha signalling modulate interferon gamma production in response to bacterial infection

Diets rich in soy phytoestrogens have many potential health benefits but isoflavones such as genistein may suppress cell mediated immune function. The effect of dietary phytoestrogens on the host response to infection has not been extensively examined. Mice were fed a diet containing soy phytoestrogens and infected with Mycobacterium avium to establish a chronic infection and inflammatory response. As phytoestrogens may act through classical oestrogen receptors (ER), mice deficient in ERalpha signalling and wild type mice were evaluated for a panel of Type 1-associated cytokines (IFNgamma, IL-12 and IL-18) in the spleen. IFNgamma production in the spleen was increased approximately 4-fold in ERalpha-deficient mice fed a casein-based diet over wild type mice fed a casein-based diet (P < 0.05), suggesting a role for ERalpha in suppressing IFNgamma production. IL-18 levels in spleens of wild type mice were decreased compared to ERalpha-deficient mice on a casein diet. Splenic IL-12 and IL-18 levels were not affected in wild type and ERalpha-deficient mice on the phytoestrogen containing diets, with the exception that whole soy increased IL-12 levels in the tissues of ERalpha deficient mice. We conclude that ERalpha and dietary phytoestrogens can influence production of key regulatory cytokines in response to chronic bacterial infection.

Mycobacterium bovis bacille Calmette-Guerin vaccination of cattle: activation of bovine CD4+ and gamma delta TCR+ cells and modulation by 1,25-dihydroxyvitamin D3

SETTING

1,25-dihydroxyvitamin D3 (1,25(OH)(2)D(3)) is a potent modulator of immune responses and may be beneficial in the treatment of tuberculosis. Recent evidence suggest that 1,25(OH)(2)D(3) may affect T-dependent responses in cattle; however, mechanisms by which this vitamin modulates activation of bovine T cells are unclear.

OBJECTIVE

Determine the effects of 1,25(OH)(2)D(3) on the expression of CD25, CD44, and CD62L by bovine T cell subsets proliferating in response to antigen stimulation.

DESIGN

Antigen-specific recall responses of Mycobacterium bovis bacille Calmette-Guerin (BCG) vaccinated cattle were used as a model system to evaluate effects of 1,25(OH)(2)D(3) on the proliferation and activation of bovine T cell subsets.

RESULTS

CD4(+) and gamma delta TCR(+) cells were the predominant T cell subsets responding to soluble crude M. bovis-derived antigens (i.e., purified protein derivative and a BCG whole cell sonicate) by proliferation and activation-induced alterations in phenotype. These subsets exhibited increased CD25 and CD44 mean fluorescence intensity (mfi) and decreased CD62L mfi upon antigen stimulation. Addition of 1,25(OH)(2)D(3) inhibited proliferation of CD4(+) cells and decreased the expression of CD44 on responding (i.e., proliferating) CD4(+) and gamma delta TCR(+) cells.

CONCLUSION

These findings suggest that the production of 1,25(OH)(2)D(3) by macrophages within tuberculous lesions would inhibit proliferation and CD44 expression by co-localized CD4(+) and gamma delta TCR(+) cells.

Identification and characterization of a novel regulatory factor: IgA-inducing protein

IgA is the predominant Ig isotype in mucosal secretions and thus plays a pivotal role in host defense. The mechanisms by which IgA expression is regulated may differ among species and involve multiple pathways. Various cytokines and costimulators have been identified which regulate expression of this isotype, including IL-10, IL-2, vasoactive intestinal peptide, and TGF-beta. We have tested a wide array of known factors, but only under very limited conditions do these factors mediate substantial IgA production in vitro from bovine B cells. In response to these findings, we generated a cDNA library in a mammalian expression vector from activated cells derived from bovine gut-associated lymphoid tissues (Peyer's patch and mesenteric lymph node cells) as a source of soluble factor(s) that may regulate IgA production. We have identified a novel factor, IgA-inducing protein, which stimulates relatively high levels of IgA production in vitro following CD40 stimulation in coculture with IL-2. Our data suggest that IgA-inducing protein regulates IgA by acting as a switch or differentiation factor and is expressed in a variety of lymphoid and nonlymphoid tissues.

Evaluation of shedding of bovine herpesvirus 1, bovine viral diarrhea virus 1, and bovine viral diarrhea virus 2 after vaccination of calves with a multivalent modified-live virus vaccine

OBJECTIVE

To determine whether bovine herpesvirus 1 (BHV1), bovine viral diarrhea (BVDV) virus 1 (BVDV1), or BVDV 2 (BVDV2) were shed after parenteral administration of a multivalent modified-live virus vaccine.

DESIGN

Prospective study.

ANIMALS

28 healthy beef calves and 4 healthy pregnant beef cows.

PROCEDURE

A commercially available modified-live virus multivalent vaccine was administered to steers and heifers (n = 18) that were seronegative to BHV1, BVDV1, and BVDV2. Four seronegative pregnant control cows were held in contact with the vaccinated calves for 103 days. Unvaccinated calves (n = 10) were held as controls in a separate double-fenced pen. Seroconversion was monitored by determining serum neutralization titers after vaccination. Viral shedding and viremia were assessed via analysis of nasal swab specimens and blood by use of polymerase chain reaction (PCR) and reverse transcriptase-PCR assays and virus isolation.

RESULTS

A transient BVDV1 viremia was detected in most vaccinated calves 3 to 10 days after vaccination. All vaccinated calves seroconverted to BVDV1 and BVDV2. Seventeen of 18 vaccinated calves seroconverted to BHV1. Viral shedding was not detected in the vaccinated calves. All control cattle remained seronegative to BHV1, BVDV1, and BVDV2 throughout the study.

CONCLUSIONS AND CLINICAL RELEVANCE

Shedding of BHV1, BVDV1, and BVDV2 after vaccination was either nonexistent or undetected and did not result in transmission of BHV1, BVDV1, or BVDV2 vaccine viruses to pregnant contact control cows.

Phenotyping of transgenic cloned piglets

Numerous reports list the abnormalities obtained from cloning sheep and cattle. To date, few reports provide detailed information regarding the overall health status and performance data of cloned animals. This report follows three litters totaling 10 transgenic cloned piglets from birth through puberty. Significant findings from physical examinations and response to treatments are included, as well as necropsy data from five of the piglets that died during the study. The birth weights, placental weights, and growth rates for this group of piglets were not different from that of control animals raised in the same environment. Hematology and serum chemistry data were collected at 2 days of age, and at 2, 4, 8, 12, 16, 20, and 24 weeks of age. Results indicated a mild anemia and hypoproteinemia in the cloned piglets from birth through 4 weeks of age, but both conditions were corrected by 8 weeks of age. Echocardiography was performed on seven of the piglets. No anatomical defects were detected, but three of the piglets had decreased cardiac output values. However, both animals are growing and show no evidence of clinical disease. The immune system was evaluated by quantification of serum IgM and IgG levels and by determining the population of B-cells, macrophages, helper T-cells (CD4), cytotoxic T-cell (CD8), and double positive T-cells (CD4/CD8). With the exception of one animal, no abnormalities were detected with the immune system of the examined piglets. During the course of this study, five of the 10 piglets were euthanized or died, indicating there is a high mortality rate among cloned piglets, but the remaining five cloned piglets are free from detectable defects.

Peripheral blood-derived bovine dendritic cells promote IgG1-restricted B cell responses in vitro

Regulation of humoral responses involves multiple cell types including the requirements for cognate interactions between T and B cells to drive CD40-dependent responses to T-dependent antigens. A third cell type has also been shown to play an essential role, the dendritic cell (DC). We demonstrate that bovine peripheral blood-derived (PB)-DC are similar in function to features described for human interstitial DC including the production of signature type 2 cytokines [interleukin (IL)-13, IL-10]. PB-DC express moderate-to-high costimulatory molecule expression, and major histocompatibility complex class II is negative for CD14 expression and has low or no expression of CD11c. Consistent with the interstitial phenotype is the ability of PB-DC to influence B cell activation and differentiation via direct expression of CD40L and type 2 cytokines. Collectively, these results suggest that direct B cell-DC interactions may promote an immunoglobulin-isotype expression pattern consistent with type 2 responses, independent of direct T cell involvement.

Type 1 and type 2 responses in regulation of Ig isotype expression in cattle

Regulation of humoral immune responses is multifactorial involving appropriate activation, costimulation and the presence of specific soluble factors. Polarized type 1 or type 2 humoral responses in the laboratory mouse have been linked to expression of specific cytokines and thus can be used to provide insight into the type of response generated by infection. For example, IFN-gamma has been linked to IgG2a and IgG3 production, IL-4 to IgG1 and IgE production and TGF-beta to IgA production. Unlike the laboratory mouse, generally housed under defined conditions, highly skewed isotype expression patterns generally occur in cattle in chronic infections. A few examples of polarized responses have been noted in chronic experimental or naturally occurring infections including F. hepatica, M. paratuberculosis, C. parvum and B. abortus. In vitro studies using purified bovine B cells and various forms of costimulation and cytokines have demonstrated that isotype responses can be polarized under certain experimental conditions in vitro. That is, IgG1 expression is positively regulated by IL-4 and IgG2 expression is positively regulated by IFN-gamma. Other as yet unidentified factors may play pivotal roles in regulating humoral immune responses in large ruminant species in vivo. This possibility is best exemplified by recent studies using DNA vaccines in cattle that have been demonstrated in the mouse to be generally polarizing to a type 1 response. Surprisingly, studies in cattle using plasmid DNA as vaccination material show an almost exclusive IgG1 response. Based on a number of studies using T cell clones and various biological assays, it is clear that the classical roles of many cytokines in the laboratory mouse do not extrapolate entirely or at all to cattle. Thus, the design of adjuvants and immune modulators should be based on studies done in cattle or using bovine cells. Based on studies to date, several "holes" in the cytokine repertoire exist and these roles may be assumed by unique factors or activities of other known cytokines.

Use of the mannan receptor to selectively target vaccine antigens for processing and antigen presentation through the MHC class I and class II pathways

Extensive studies have shown that synthetic and recombinant vaccines developed against hemoparasites have not been as effective as whole parasites or crude membrane fractions in eliciting protective immunity. A possible reason is that synthetic vaccines are not being presented in a form that induces the appropriate immune response. We have developed a bovine model system to evaluate the ability of adjuvant compounds to induce an immune response to peptide antigens dominated by a cytokine profile with a Type 1 (cell-mediated) or Type 2 (humoral) bias. In the initial testing of this system, we found that mRNA expression of certain cytokines (interleukin [IL]-1beta, IL-6, IL-12, IL-15, GM-CSF, iNOS, and tumor necrosis factor [TNF]-alpha) is enhanced when monocyte-derived macrophages are stimulated with peptide antigen conjugated with mannan under oxidizing conditions compared to peptide conjugated with reduced mannan. The data suggest this model will be useful in identifying adjuvant systems that selectively modulate the cytokine profile of antigen presenting cells at the time of antigen presentation and the consequent downstream maturation of naive T cells to effector cells with Type 1 or Type 2 cytokine bias.

Enhancing effects of anti-CD40 treatment on the immune response of SCID-bovine mice to Trypanosoma congolense infection

African trypansosomes are tsetse-transmitted parasites of chief importance in causing disease in livestock in regions of sub-Saharan Africa. Previous studies have demonstrated that certain breeds of cattle are relatively resistant to infection with trypanosomes, and others are more susceptible. Because of its extracellular location, the humoral branch of the immune system dominates the response against Trypanosoma congolense. In the following study, we describe the humoral immune response generated against T. congolense in SCID mice reconstituted with a bovine immune system (SCID-bo). SCID-bo mice infected with T. congolense were treated with an agonistic anti-CD40 antibody and monitored for the development of parasitemia and survival. Anti-CD40 antibody administration resulted in enhanced survival compared with mice receiving the isotype control. In addition, we demonstrate that the majority of bovine IgM+ B cells in SCID-bo mice expresses CD5, consistent with a neonatal phenotype. It is interesting that the percentage of bovine CD5+ B cells in the peripheral blood of infected SCID-bo mice was increased following anti-CD40 treatment. Immunohistochemical staining also indicated increased numbers of Ig+ cells in the spleens of anti-CD40-treated mice. Consistent with previous studies demonstrating high IL-10 production during high parasitemia levels in mice and cattle, abundant IL-10 mRNA message was detected in the spleens and peripheral blood of T. congolense-infected SCID-bo mice during periods of high parasitemia. In addition, although detected in plasma when parasites were absent or low in number, bovine antibody was undetectable during high parasitemia. However, Berenil treatment allowed for the detection of VSG-specific IgG 14 days postinfection in T. congolense-infected SCID-bo mice. Overall, the data indicate that survival of trypanosome-infected SCID-bo mice is prolonged when an agonistic antibody against bovine CD40 (ILA156) is administered. Thus, stimulation of B cells and/or other cell types through CD40 afforded SCID-bo mice a slight degree of protection during T. congolense infection.

Natural killer cells express estrogen receptor-alpha and estrogen receptor-beta and can respond to estrogen via a non-estrogen receptor-alpha-mediated pathway

Natural killer (NK) cells play a crucial role in host defense against pathogens and immune surveillance against cancer. Given that estrogens have been reported to suppress NK cell activity, we sought to elucidate the mechanisms by which estrogen mediates this effect. We demonstrate by immunocytochemical staining with estrogen receptor-alpha (ERalpha)- and estrogen receptor-beta (ERbeta)-specific antibodies that both ERalpha and ERbeta are expressed in murine NK cells. We also compared the ability of high doses of 17beta-estradiol ( approximately 800 pg/ml) to regulate NK cell activity in wild-type and estrogen receptor-alpha-deficient (ERalphaKO) mice. 17beta-estradiol elicited a significant decrease in NK cell activity in both wild-type and ERalphaKO mice (P < 0.001). These data suggest that ERbeta or possibly a novel receptor is involved in mediating estrogen action on NK cell activity and raise the potential for therapeutic modulation of NK cell activity with selective estrogen receptor modulators (SERMS).

Induction of interleukin-6 and interleukin-12 in bovine B lymphocytes, monocytes, and macrophages by a CpG oligodeoxynucleotide (ODN 2059) containing the GTCGTT motif

Bacterial DNA and synthetic oligodeoxynucleotides (ODN) that contain unmethylated CpG dinucleotides flanked by certain bases (CpG ODN) have been shown to activate murine and human B cells and to induce proinflammatory cytokines by monocytes/macrophages and dendritic cells (DC). However, the CpG ODN sequences optimal for mice and humans are different. In the current study, the effects of CpG ODN, which were defined to stimulate strong responses in either mouse or human leukocytes, were compared for stimulation of bovine B lymphocyte proliferation and macrophage cytokine mRNA expression. The optimal CpG ODN was then tested for induction of cytokines in peripheral blood mononuclear cells (PBMC) and purified B lymphocytes, monocytes, and macrophages. At a high ODN concentration (40 microM), all but two CpG ODN tested stimulated B cell proliferation, which was dependent on unmethylated CpG motifs. CpG ODN 2059 containing the GTCGTT motif shown to activate human leukocytes also promoted the highest level of bovine B cell proliferation at a lower concentration (10 microM) when compared with CpG ODN containing AACGTT or GACGTT motifs active for murine leukocytes. Furthermore, ODN 2059 induced interleukin-6 (IL-6) production by B lymphocytes and IL-6 and IL-12 production by PBMC, monocytes, and macrophages. In contrast, IL-1beta and tumor necrosis factor-alpha (TNF-alpha) production was either very low or undetectable. Consistent with increased IL-12 production, ODN 2059 also stimulated interferon-gamma (IFN-gamma) production by PBMC. Importantly, the levels of cytokines induced by ODN 2059 were comparable to those generated in response to Escherichia coli DNA. The weak TNF-alpha response combined with the vigorous IL-6 and IL-12 response to ODN 2059 indicate the potential use of this CpG ODN as an adjuvant to enhance both antibody-mediated and IFN-gamma-mediated macrophage activation, which are important for protection against disease caused by intracellular pathogens of cattle.

The identification and characterization of a ligand for bovine CD5

CD5, a type I glycoprotein expressed by T cells and a subset of B cells, is thought to play a significant role in modulating Ag receptor signaling. Previously, our laboratory has shown that bovine B cells are induced to express this key regulatory molecule upon Ag receptor cross-linking. To date, a ligand has not been described for bovine CD5. Given the importance ligand binding presumably plays in the functioning of CD5 on this B cell subset and on T cells, we sought to characterize the ligand for this protein using a bovine CD5-human IgG1 (CD5Ig) fusion protein produced by both mammalian and yeast cells. As determined by CD5Ig binding, expression of this ligand is negative to low on freshly isolated lymphocytes, with low-density expression being limited to activated B cells. Activation with LPS, PMA, and calcium ionophore, or ligation of CD40 alone or in combination with anti-IgM, resulted in B cell-specific expression of this ligand. Interestingly, activation through B cell Ag receptor cross-linking alone, although able to induce CD5 expression, did not result in expression of CD5 ligand (CD5L). In addition, we demonstrate a functional role for CD5L as a costimulatory molecule that augments CD40L-stimulated B cell proliferation. Finally, immunoprecipitation with CD5Ig suggests that the ligand characterized in this study has a molecular mass of approximately 200 kDa. The data reported herein, as well as future studies aimed at further characterizing this newly identified bovine CD5L, will undoubtedly aid in understanding the role that the CD5-CD5L interaction plays in immune responses.

The P2X7 purinergic receptor on bovine macrophages mediates mycobacterial death

P2X7 is an ATP gated purinoceptor that has been linked to various immune responses. P2X7 appears to be expressed ubiquitously in the immune system and thus may be important as an effector pathway or play significant roles in cell activation/death. 2',3'-(4-Benzoyl)benzoyl ATP is the most potent agonist of this receptor and ATP in its fully dissociated form (ATP(4-)) also activates the receptor. High concentrations of ATP can cause the P2X7 receptor to induce pore formation on the surface of the cell that allows molecules of considerable size to pass and can lead to cell death. The P2X7 receptor has also been linked to various immune activities when the concentration of ATP is lower, including the release of IL-1beta. The role P2X7 receptors have on immune cell activities is just beginning to be understood. We sought to determine the role of P2X7 on bovine macrophages in eliminating the causative agent of bovine-type tuberculosis, Mycobacterium bovis. Because high concentrations of ATP are linked to macrophage death, we determined if this method of cell destruction also leads to reduced bacterial viability. We find that P2X7 is present on bovine macrophages from different sources, including both peripheral blood-derived as well as alveolar macrophages. In addition, P2X7 mRNA is present in B and T lymphocytes. The treatment of M. bovis-infected macrophages with ATP results in reduced macrophage viability as well as reduced M. bovis viability.

Pathogenesis of herpes simplex virus type 1-induced corneal inflammation in perforin-deficient mice

Herpetic stromal keratitis (HSK) is an inflammatory disease of the cornea that often results in blindness. It is mediated by a host immune response which is triggered by herpes simplex virus (HSV) infection. Immune effector mechanisms are hypothesized to be important in disease development. We investigated, in a mouse model, whether perforin-dependent cytotoxicity is an important effector mechanism in the production of HSK. Wild-type (C57BL/6) and perforin-deficient (PKO) mice were infected intracorneally with HSV-1 strain F. Clinical disease and histologic lesions of the cornea at 23 days postinfection (p.i.) were significantly less severe in HSV-1-infected PKO mice than in infected wild-type mice. mRNA for the chemokine macrophage inflammatory protein 1alpha (MIP-1alpha) was detected by reverse transcription-PCR in the corneas of infected wild-type mice but not in the corneas of infected PKO mice at 23 days p.i. Adoptive transfer of wild-type HSV-1 immune T-cell-enriched splenocytes into HSV-1-infected PKO mice restored the disease phenotype which was seen in infected wild-type mice. In contrast, mice carrying a null-function mutation in the Fas ligand, which is involved in an alternative cytotoxic mechanism, developed clinical disease and histologic lesions which were comparable to those in wild-type mice. Viral clearance from the eyes of PKO mice was not impaired. There was no significant difference between the infectious viral titers isolated from the eyes of PKO and wild-type mice. Our findings show that perforin is important in the pathogenesis of HSK.

Activation of bovine B cells via surface immunoglobulin M cross-linking or CD40 ligation results in different B-cell phenotypes

Experiments reported herein demonstrate that activation of bovine B cells via surface immunoglobulin M (sIgM) cross-linking, analogous to T-cell independent (TI-2) antigenic stimulation, results in the expression of CD5. Interestingly, in the presence of CD40 ligand, sIgM-mediated induction of CD5 on B cells was inhibited. These findings indicate that activation of bovine B cells via B-cell receptor (BCR) cross-linking results in a CD5+ B-cell phenotype and that CD40 signalling is inhibitory to this process. Analysis of cytokine mRNA indicates that bovine B cells constitutively express tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1beta transcripts in vitro, while IL-10 mRNA expression is induced following sIgM cross-linking. IL-12 p40 transcripts were produced by B cells activated by CD40, but not by BCR, ligation. Analysis of cytokine receptor mRNA indicates that activation through CD40, in the presence or absence of IgM cross-linking, results in increased IL-4 receptor-alpha (IL-4Ralpha), IL-13Ralpha1 and interferon-alpha receptor 1 (IFN-alphaR1) mRNA levels. Overall, these findings suggest that activation of bovine B cells through BCR cross-linking yields an activation phenotype that differs substantially from that of B cells activated through CD40.