Pro-inflammatory capacity of Escherichia coli O104:H4 outbreak strain during colonization of intestinal epithelial cells from human and cattle.

In 2011, Germany was struck by the largest outbreak of hemolytic uremic syndrome. The highly virulent E. coli O104:H4 outbreak strain LB226692 possesses a blended virulence profile combining genetic patterns of human adapted enteroaggregative E. coli (EAEC), rarely detected in animal hosts before, and enterohemorrhagic E. coli (EHEC), a subpopulation of Shiga toxin (Stx)-producing E. coli (STEC) basically adapted to the ruminant host. This study aimed at appraising the relative level of adaptation of the EAEC/EHEC hybrid strain LB226692 to humans and cattle. Adherence and invasion of the hybrid strain to intestinal (jejunal and colonic) epithelial cells (IEC) of human and bovine origin was compared to that of E. coli strains representative of different pathovars and commensal E. coli by means of light and electron microscopy and culture. Strain-specific host gene transcription profiles of selected cytokines and chemokines as well as host-induced transcription of bacterial virulence genes were assessed. The release of Stx upon host cell contact was quantified. The outbreak strain's immunomodulation was assessed by cultivating primary bovine macrophages with conditioned supernatants from IEC infection studies with E. coli, serving as model for the innate immunity of the bovine gut. The outbreak strain adhered to IEC of both, human and bovine origin. Electron microscopy of infected cells revealed the strain's particular affinity to human small IEC, in contrast to few interactions with bovine small IEC. The outbreak strain possessed a high-level of adhesive power, similar to human-associated E. coli strains and in contrast to bovine-associated STEC strains. The outbreak strain displayed a non-invasive phenotype, in contrast to some bovine-associated E. coli strains, which were invasive. The outbreak strain provoked some pro-inflammatory activity in human cells, but to a lower extent as compared to other pathotypes. In contrasts to bovine-associated E. coli strains, the outbreak strain induced marked pro-inflammatory activity when interacting with bovine host cells directly (IEC) and indirectly (macrophages). Among stx2-positive strains, the human-pathogenic strains (LB226692 and EHEC strain 86-24) released higher amounts of Stx compared to bovine-associated STEC. The findings imply that the outbreak strain is rather adapted to humans than to cattle. However, the outbreak strain's potential to colonize IEC of both host species and the rather mixed reaction patterns observed for all strains under study indicate, that even STEC strains with an unusual genotype as the EHEC O104:H4 outbreak strain, i.e. with an EAEC genetic background, may be able to conquer other reservoir hosts.

Mycobacterium tuberculosis exposure of livestock in a German dairy farm: implications for intra vitam diagnosis of bovine tuberculosis in an officially tuberculosis-free country.

Germany has been an officially bovine tuberculosis (bTB)-free (OTF) country since 1996. Gradually rising numbers of bTB herd incidents due to Mycobacterium bovis and M. caprae in North-Western and Southern Germany during the last few years prompted the competent authorities to conduct a nationwide bTB survey in 2013/2014. This led to the detection of a dairy herd in which as many as 55 cattle reacted positively to consecutive intra vitam testing. Test-positive animals lacked visible lesions indicative of bTB at necropsy. Extensive mycobacterial culturing as well as molecular testing of samples from 11 tissues for members of the M. tuberculosis complex (MTC) yielded negative results throughout. However, caseous lymphadenitis of Ln. mandibularis accessorius was observed during meat inspection of a fattening pig from the same farm at regular slaughter at that time. Respective tissue samples tested MTC positive by polymerase chain reaction, and M. tuberculosis T1 family were identified by spoligotyping. Four human reactors within the farmer's family were also found to be immunoreactive. As exposure of livestock to M. tuberculosis is not generally considered, its impact may result in regulatory and practical difficulties when using protocols designed to detect classical bTB, particularly in OTF countries.

Dexamethasone depletes gammadelta T cells and alters the activation state and responsiveness of bovine peripheral blood lymphocyte subpopulations.

Administration of dexamethasone (DEX) to cattle is commonly used in models of stress-induced effects on host defense, including models investigating interactions of microorganisms with their host. Much less is known about the effects of DEX on the adaptive immune response in cattle compared with other species. The objective of the present study was to characterize subsets of circulating lymphocytes in calves before and 48 h after the onset of parenteral DEX treatment. Treatment significantly reduced the overall percentage of circulating lymphocytes and disproportionately depleted the population of gammadeltaTCR(+)/CD8alpha(-) cells. Analysis within the CD8alpha(+) population of T cells revealed that DEX treatment also reduced the CD8alpha(low) subset of gammadeltaT cells coexpressing the activation marker ACT-2(+). By contrast, DEX treatment did not affect the percentage of CD8alpha(low)/CD25(+) cells, indicating that cells with a special activation state were affected. Dexamethasone treatment reduced the number of gammadeltaT cells but increased the percentages of CD14(+) monocytes and activated CD25(+) cells (both CD4(-) and CD4(+)) in peripheral blood mononuclear cell (PBMC) preparations. Although DEX treatment reduced the overall proliferative capacity of PBMC, it enhanced the relative number of proliferating CD4(+) lymphocytes. Lower levels of mRNA for several Th-prototype cytokines (IL-2, IFN-beta, IL-4, transforming growth factor-beta) were detected in short-term PBMC cultures established from DEX-treated calves compared with PBMC cultures from control calves; the amount of il-10 transcripts, however, was unaffected. Results of the study reported here clearly show that DEX treatment does not uniformly suppress the bovine immune system but has differential effects on lymphocyte sub-populations and functions. This information must be considered when using DEX treatment as a bovine stress model.

Faecal Escherichia coli as biological indicator of spatial interaction between domestic pigs and wild boar (Sus scrofa) in Corsica.

On the Mediterranean island of Corsica, cohabitation between sympatric domestic pigs and Eurasian wild boar (Sus scrofa) is common and widespread and can facilitate the maintenance and dissemination of several pathogens detrimental for the pig industry or human health. In this study, we monitored a population of free-ranging domestic pigs reared in extensive conditions within a 800-ha property located in Central Corsica which was frequently visited by a sympatric population of wild boar between 2013 and 2015. We used GPS collars to assess evidence of a spatially shared environment. Subsequently, we analysed by PFGE of XbaI-restricted DNA if those populations shared faecal Escherichia coli clones that would indicate contact and compared these results with those collected in a distant (separated by at least 50 km) population of wild boar used as control. Results showed that one of eight wild boars sampled in the study area shed E. coli XbaI clones identical to clones isolated from domestic pig sounders from the farm, while wild boar populations sampled in distant parts of the study area shared no identical clone with the domestic pigs monitored. Interestingly, within the sampled pigs, two identical clones were found in 2013 and in 2015, indicating a long-time persisting colonization type. Although the method of isolation of E. coli and PFGE typing of the isolates requires intensive laboratory work, it is applicable under field conditions to monitor potential infectious contacts. It also provides evidence of exchange of microorganisms between sympatric domestic pigs and wild boar populations.

Bovine caruncular epithelial cell line (BCEC-1) isolated from the placenta forms a functional epithelial barrier in a polarised cell culture model.

In the bovine synepitheliochorial placenta key sites of fetal-maternal interaction are placentomes consisting of maternal caruncles interdigitating with fetal cotyledons. The aim of this study was to establish an epithelial cell line from caruncles of pregnant cows and to develop a model to study restricted trophoblast invasion, pathogenesis of pregnancy associated diseases and pathways of infection and transport. Primary epithelial cells were isolated, successfully subcultured for 32 passages and cryopreserved at various stages. The cultures were termed bovine caruncular epithelial cell line-1 (BCEC-1). Cytokeratin, zonula occludens-1 protein and vimentin but neither alpha-smooth muscle actin nor desmin were detected by immunofluorescence performed every 5 (+/-1) passages. These results were confirmed by Western blotting. BCEC-1 were then cultured either without matrix or on fibronectin or collagen coated Transwell polyester membrane inserts, respectively, enabling separate access to the basal or apical epithelial compartments. Transmission and scanning electron microscopy of BCEC-1 revealed ultrastructural features also observed in vivo, such as apical microvilli and junctional complexes. Transepithelial electrical resistance (TEER) was measured regularly and revealed an increase with advancing confluence in all cultures. Cultures on coated inserts reached confluence and corresponding TEER-levels at an earlier stage. In addition, the cells were tested negative for bovine virus diarrhoea (BVD) virus, but were permissive for the virus. In conclusion, the BCEC-1 cell line retained characteristics of maternal caruncular epithelial cells as observed in vivo and in primary cell cultures and thus will be a highly useful tool for future studies of pathways of invasion, fetal-maternal communication, transport and infection.

Nationwide Cross-Sectional Study on Bovine Tuberculosis by Intra Vitam Testing in Germany, 2013-2014.

Germany was declared officially free from bovine tuberculosis (bTB) effective from 1 July 1996. After the occurrence of several Mycobacterium (M.) bovis outbreaks in north-western Germany in recent years with high intraherd prevalence at the time of detection, the reliability of abattoir surveillance as the principal component of the national bTB control programme was debated by veterinary public health officials. Rising numbers of wildlife-associated outbreaks caused by M. caprae in southern Germany eventually prompted a nationwide cross-sectional study on bTB. A total of 51 999 cattle, that is 0.41% of the national herd kept on 1.73% of German cattle farms, were tested. Despite 4 positive and 152 inconclusive single intradermal comparative cervical test results, none of the animals was confirmed as bTB-positive by a subsequent interferon-release assay or by post-mortem PCR testing. The estimated prevalence of bTB in Germany was thus calculated as 0.0% (CI 0.0000-0.0064%) affirming that Germany still qualifies as an officially tuberculosis-free (OTF) country. Occasional randomized nationwide testing can be an appropriate tool to reassure the OTF status and may also help to maintain an appropriate training level for the diagnostic procedures and for supporting sustained disease awareness among stakeholders.

Effect of lactoferrin on release and bioactivity of Shiga toxins from different Escherichia coli O157:H7 strains.

Prevention of enterohemorrhagic Escherichia coli (EHEC) O157:H7 infections and of their severe clinical sequelae in humans remain to be a current challenge. Administration of bovine lactoferrin (bLF) proved to be effective in clearing EHEC from the bovine intestine, an important EHEC reservoir, suggesting that bLF may also be beneficial in human application against EHEC infections. To estimate the biological safety of this approach, we analyzed the effects of bLF on the main EHEC virulence factor, Shiga toxin (Stx). We quantified the release of Stx 1 and 2 from two O157:H7 EHEC strains (Stx1+Stx2+ and Stx2+ producing, respectively) cultured in the presence of bLF using ELISA assays and assessed cytotoxic effects of bLF and co-cultured EHEC on Vero cells. Effects of bLF on the stability of Stx2 were investigated using western blotting. ELISA results indicate a bLF concentration-dependent decrease of active, cell-free Stx2, but not Stx1 in EHEC cultures. High concentrations (100 and 50mg/ml) of bLF resulted in significantly reduced (p<0.05) metabolic activity rates of Vero cells, whereas a concentration of 10mg/ml bLF was considered non-toxic for Vero cells. At concentrations of 1 or 0.1mg/ml, bLF mitigated the verocytotoxicity of EHEC strains in a co-culture model up to 48h after inoculation. When only colonizing bacteria were taken into account, cytotoxicity could be significantly reduced by 10 and 1mg/ml bLF during 48h. This effect of bLF at least partly results from degradation of the Stx2 receptor-binding B-subunit.

Experimental Evaluation of Faecal Escherichia coli and Hepatitis E Virus as Biological Indicators of Contacts Between Domestic Pigs and Eurasian Wild Boar.

Domestic pigs and Eurasian wild boar (Sus scrofa) share several important viral and bacterial pathogens. Therefore, direct and indirect contacts between domestic pigs and wild boar present a risk of pathogen spillover and can lead to long-term perpetuation of infection. Biological indicators could be a powerful tool to understand and characterize contacts between wild boar and domestic pigs. Here, faecal Escherichia coli and Hepatitis E virus (HEV) were explored as potential biological indicators under experimental conditions. The data gained in our pilot study suggest that faecal E. coli can be used as biological indicator of contact between wild boar and domestic pig. For HEV, faecal transmission was also confirmed. However, molecular studies on full-genome basis did not reveal markers that would allow tracing of transmission direction. Based on these promising results, future field studies will especially target the practicability of E. coli microbiome molecular typing as surrogate of contacts at the wildlife-livestock interface.

Experimental Infection of Calves with Escherichia coli O104:H4 outbreak strain.

In 2011, a severe outbreak of hemolytic-uremic syndrome was caused by an unusual, highly virulent enterohemorrhagic E. coli (EHEC) O104:H4 strain, which possessed EHEC virulence traits in the genetic background of human-adapted enteroaggregative E. coli. To determine magnitude of fecal shedding and site of colonization of EHEC O104:H4 in a livestock host, 30 (ten/strain) weaned calves were inoculated with 10(10) CFU of EHEC O104:H4, EHEC O157:H7 (positive control) or E. coli strain 123 (negative control) and necropsied (4 or 28 d.p.i.). E. coli O157:H7 was recovered until 28 d.p.i. and O104:H4 until 24 d.p.i. At 4 d.p.i., EHEC O104:H4 was isolated from intestinal content and detected associated with the intestinal mucosa. These results are the first evidence that cattle, the most important EHEC reservoir, can also carry unusual EHEC strains at least transiently, questioning our current understanding of the molecular basis of host adaptation of this important E. coli pathovar.

Nest predation increases with parental activity: separating nest site and parental activity effects.

Alexander Skutch hypothesized that increased parental activity can increase the risk of nest predation. We tested this hypothesis using ten open-nesting bird species in Arizona, USA. Parental activity was greater during the nestling than incubation stage because parents visited the nest frequently to feed their young during the nestling stage. However, nest predation did not generally increase with parental activity between nesting stages across the ten study species. Previous investigators have found similar results. We tested whether nest site effects might yield higher predation during incubation because the most obvious sites are depredated most rapidly. We conducted experiments using nest sites from the previous year to remove parental activity. Our results showed that nest sites have highly repeatable effects on nest predation risk; poor nest sites incurred rapid predation and caused predation rates to be greater during the incubation than nestling stage. This pattern also was exhibited in a bird species with similar (i.e. controlled) parental activity between nesting stages. Once nest site effects are taken into account, nest predation shows a strong proximate increase with parental activity during the nestling stage within and across species. Parental activity and nest sites exert antagonistic influences on current estimates of nest predation between nesting stages and both must be considered in order to understand current patterns of nest predation, which is an important source of natural selection.

Globotriaosylceramide (Gb(3)/CD77) is synthesized and surface expressed by bovine lymphocytes upon activation in vitro.

Neutral glycosphingolipids (GSLs) are considered activation markers on human lymphocytes, which are fundamental for studying the immune system. For cattle, only a limited number of activation markers has yet been identified. We recently showed that Shiga toxin 1, known to use globotriaosylceramide (Gb(3) syn. CD77) as a cellular receptor, depresses proliferation of activated bovine lymphocytes [Infect. Immunol. 67 (1999b) 2209]. In order to confirm the expression of Gb(3)/CD77 on bovine lymphocytes, we flowcytometrically examined a bovine B-lymphoma cell line (BL-3) and bovine peripheral blood mononuclear cells (PBMC) before and after mitogenic stimulation and biochemically characterized neutral GSLs extracted from PBMC. CD77 was detected on the surface of BL-3 cells and cultured PBMC essentially after mitogenic stimulation. Although expressed by all PBMC subpopulations identified, the portion of CD7+ cells was highest for BoCD8+ cells, followed by B-cells and BoCD4+ cells at day 4 of cultivation. Ceramide trihexoside of stimulated PBMC was structurally determined as Gal(alpha1-4)Gal(1-4)Glc(1-1)ceramide (Gb(3)). Biochemically, Gb(3) was also detected within unstimulated PBMC which contained ceramide monohexoside (CMH) and Gb(3) in a ratio of about 4:1. However, stimulation induced an increase of CMH and Gb(3) by a factor of 2.5 and 10, respectively, implicating that bovine lymphocytes regulate surface expression of Gb(3)/CD77 predominantly by quantitative changes in the Gb(3) metabolism. This report presents Gb(3)/CD77 as the first GSL identified on bovine immune cells and highly recommends this activation dependent antigen as a useful tool to investigate lymphocyte activation within the bovine immune system.

Compensation of preliminary blood phagocyte immaturity in the newborn calf.

To estimate the functional maturity of the phagocytic defence in neonatal calves, we analyzed the characteristics of blood phagocytes from calves (n = 10) 1 h post partum (p.p.) and 4 h p.p. At 1 h p.p., all calves were colostrum-deprived, while 5 calves had received colostrum before the 4 h p.p. sampling. The results were compared to those obtained from 3-9-week-old calves (n = 10). Phagocytic and oxidative burst activity of polymorphonuclear leukocytes (PMNL) and monocytes were determined in whole blood and separately analyzed by flow cytometry. In neonates prior to colostrum ingestion (1 h p.p.), phagocytic activity of PMNL against non-preopsonized E. coli was lower when compared to PMNL of 3-9-week-old calves. Opsonization of bacteria with pooled plasma from adult animals only partially restituted this lower PMNL phagocytic activity, indicating that humoral as well as cellular aspects of PMNL phagocytosis are altered in neonatal calves. In contrast to PMNL, monocytes of neonates exhibited an enhanced phagocytic activity. The oxidative burst activity of PMNL, as well as of monocytes was higher in newborn calves. During the first 4 h of life, the activities of blood phagocytes changed. Colostrum ingestion was accompanied by an increase in the percentage of phagocytizing PMNL and monocytes. This increase was absent in colostrum-deprived calves. In contrast, the oxidative burst activity of phagocytes decreased with age. In monocytes, the decrease of oxidative burst activity was only observed in colostrum-fed calves. In conclusion, some blood phagocyte functions in calves were found to be immature at birth, but these functions are presumably compensated by high absolute PMNL numbers and by other the more active mechanisms.

[The immune response in edema disease of weaned piglets measured with a recombinant B subunit of shiga-like toxin II]. / Untersuchungen zur Immunantwort bei der Odemkrankheit von Absetzferkeln mit einer rekombinanten B-Untereinheit des Shiga-like-Toxins-II.

An outbreak of edema disease (ED) was monitored in 80 piglets after weaning over a period of 4 weeks. The shedding of Shiga-like toxin-IIe) producing Escherichia coli strains, the serum bactericidal activity (SBA) against SLTEC-IIe, and the antibody response against SLT-IIe were investigated. The antibody response was monitored by utilizing a glutathione-S-transferase (GST) + SLT-IIe B/SUB fusion protein (FRANKE et al., in press) for immunoblot assays. E. coli-strain GO15III (0141:K85ac) was diagnosed as SLT-IIe-producing E. coli by polymerase chain reaction, DNA hybridization and cytotoxicity assays. Maximum excretion of GO15III appeared between days 8 and 15 after weaning. On day 1 after weaning no piglet shed GO15III, while the number increased on day 8 to 53 (66.2%) and on day 15 to 59 (73.8%) of the piglets. 4 week after weaning, GO15III was only isolated from 23 (28.8%) of the piglets. In parallel, serum bactericidal activity against GO15III increased significantly in the sera of 73 (91.2%) piglets, reaching a stable maximum from day 15 on. During the first two weeks after weaning, no piglet yielded detectable SLT-IIe-IgG. However, the number of SLT-IIe-IgG positive piglets increased steadily from day 15. On day 15, 5 (6.2%) piglets were positive in SLT-IIe immunoblot analysis and 29 days after weaning the number increased to 31 (38.8%). These data represent the first serological monitoring of a natural outbreak of edema disease in piglets after weaning by using a recombinant fusion protein (GST+SLT-IIe B/SUB). The recombinant protein proved to be a useful diagnostical tool for monitoring the specific antibody status of piglets.

[Tuberculosis in cattle - surprisingly re-emerging or continuously present?]. / Die Tuberkulose des Rindes - überraschend wieder oder immer noch präsent?

Tuberculosis in cattle, caused by Mycobacterium (M.) bovis/M. caprae, is globally one of the most important zoonotic diseases in cattle. It was widespread in Germany until the second half of the 20th century. Due to the effective control and eradication campaigns in Germany, the epidemic was almost eradicated. Consequently, Germany was regarded as essentially tuberculosis free since the end of 1961 (West) and the end of 1978 (East). By declaring the unified Germany "officially free of tuberculosis" (OTF) in 1996, freedom from tuberculosis was officially ratified by the European Commission. The prerequisite was the detection of tuberculosis in less than 0.1% of the cattle holdings per year in Germany. This status has been steadily maintained hitherto, thus resulting in some loss of awareness of bovine tuberculosis by veterinarians, farmers and the public over many decades. After 1996, the number of notified outbreaks had been on average less than 10 per 200,000 cattle holdings per year for many years. It was the year 2008 when the numbers increased. Based in part on subsequently enhanced ante mortem testing efforts, 46 outbreaks were notified in 2013. Bavaria and Lower Saxony were the federal states with the highest number of cases. Consequently, the national tuberculosis regulation was revised in 2009, 2012 and 2013 to form the basis for a modification of tuberculosis surveillance. Regionally, an improvement of the control strategy was considered necessary. In addition to the traditionally applied examination and detection methods of the tuberculin skin test (ante mortem) and bacteriological culture (post mortem), the gamma-interferon-release assay (ante mortem) and the molecular detection of the causative pathogen (post mortem) were introduced into the official collection of recommended methods. Consequently, the diagnostic procedure of tuberculosis has been accelerated. However, in many cases the increase in the range of available test systems did not increase the ease in the interpretation of results.

Flow cytometric detection of Mycobacterium avium subsp. paratuberculosis-specific antibodies in experimentally infected and naturally exposed calves.

A desirable test to diagnose infections with Mycobacterium avium subsp. paratuberculosis facilitates identification of infected cattle prior to the state of M. avium subsp. paratuberculosis shedding. This study aimed at adjusting a flow cytometry (FC)-based assay, using intact M. avium subsp. paratuberculosis bacteria as the antigen, for diagnosis of M. avium subsp. paratuberculosis infections in calves. Serum samples were collected from experimentally infected (n = 12) and naturally exposed (n = 32) calves. Samples from five calves from positive dams were analyzed to determine the dynamics of maternal antibodies. Samples from adult cattle with defined infection status served as the standard (18 M. avium subsp. paratuberculosis shedders, 22 M. avium subsp. paratuberculosis free). After preadsorption with Mycobacterium phlei, sera were incubated with M. avium subsp. paratuberculosis and M. avium subsp. avium bacterial suspensions, respectively, followed by the separate detection of bovine IgG, IgG1, IgG2, and IgM attached to the bacterial surface. M. avium subsp. paratuberculosis-specific sample/positive (S/P) ratios were compared to enzyme-linked immunosorbent assay (ELISA) S/P ratios. In adult cattle, the FC assay for IgG1 had a sensitivity of 78% at a specificity of 100%. Maternally acquired antibodies could be detected in calves up to 121 days of life. While all but two sera taken at day 100 ± 10 postnatum from naturally exposed calves tested negative, elevated S/P ratios (IgG and IgG1) became detectable from 44 and 46 weeks postinoculation onwards in two calves infected experimentally. Even with the optimized FC assay, M. avium subsp. paratuberculosis-specific antibodies can only occasionally be detected in infected calves less than 12 months of age. The failure to detect such antibodies apparently reflects the distinct immunobiology of M. avium subsp. paratuberculosis infections rather than methodological constraints.

Shiga toxin 1 from Escherichia coli blocks activation and proliferation of bovine lymphocyte subpopulations in vitro.

Shiga toxin-producing Escherichia coli (STEC) is widespread in the cattle population, but the clinical significance of Shiga toxins (Stx's) for the bovine species remains obscure. Since Stx's exert immunomodulating effects in other species, we examined the effect of purified Stx1 on a bovine B lymphoma cell line (BL-3) and peripheral blood mononuclear cells (PBMC) isolated from adult bovine blood by viability assays and flow cytometry analysis. Stx1 markedly induced apoptosis in stimulated BL-3 cells. The susceptibility of this B-cell-derived cell line was induced only by either lipopolysaccharide (LPS) or pokeweed mitogen, while cultures stimulated with T-cell mitogens were unaffected by the toxin. In contrast, Stx1 did not induce cellular death-neither apoptosis nor necrosis-in primary cultures of PBMC but hindered the mitogen-induced increase in metabolic activity. The influence of Stx1 on single PBMC subpopulations varied with the type of mitogenic stimulus applied. Stimulation with phytohemagglutinin P particularly induced the proliferation of bovine CD8-expressing (BoCD8(+)) cells, and this proliferative response was blocked by Stx1. On the other hand, Stx1 reduced the portion of viable B cells in the presence of LPS. Modulation of activation marker expression (BoCD25 and BoCD71) by Stx1 indicated that the toxin hindered the proliferation of cells by blocking their activation. In conclusion, we assume that Stx1 contributes to the pathogenesis of STEC-associated diarrhea in calves by suppressing the mucosa-associated immune response. The usefulness of cattle as a model in which to study Stx-induced immunomodulation is discussed.

Phenotypical characterization of peripheral blood leucocytes in the newborn calf.

The present study was undertaken to establish reference values for the composition of blood leucocyte populations in neonatal calves by differential leucocyte counts and immunophenotyping. Neonatal calves 1 h post partum (p.p.) were found to have a very high absolute number of granulocytes while the number of peripheral blood mononuclear cells was lower than in calves aged 3-9 weeks. The relative numbers of T cell subpopulations were similar in newborn and older calves, but newborn calves had lower percentages of B cells and MHC class II positive cells. Within the first 4 h of life the relative numbers of CD2+, CD6+, and CD8+ T cells declined in colostrum-fed as well as in colostrum-deprived calves. In contrast, the percentage of MHC class II positive cells and monocytes increased from 1 h to 4 h p.p. particularly in colostrum-fed calves. Although there is some evidence for immaturity of lymphocytes in neonatal calves, the immune system of these animals seems to be fully present at birth.