Campylobacter jejuni produces a toxin called cytolethal distending toxin (CDT). The genes encoding this toxin in C. jejuni 81-176 were cloned and sequenced. The nucleotide sequence of the genes revealed that there are three genes, cdtA, cdtB, and cdtC, encoding proteins with predicted sizes of 30,116, 28,989, and 21,157 Da, respectively. All three proteins were found to be related to the Escherichia coli CDT proteins, yet the amino acid sequences have diverged significantly. All three genes were required for toxic activity in a HeLa cell assay. HeLa cell assays of a variety of C. jejuni and C. coli strains suggested that most C. jejuni strains produce significantly higher CDT titers than do C. coli strains. Southern hybridization experiments demonstrated that the cdtB gene is present on a 6.0-kb ClaI fragment in all but one of the C. jejuni strains tested; the cdtB gene was on a 6.9-kb ClaI fragment in one strain. The C. jejuni 81-176 cdtB probe hybridized weakly to DNAs from C. coli strains. The C. jejuni 81-176 cdtB probe did not hybridize to DNAs from representative C. fetus, C. lari, C. "upsaliensis," and C. hyointestinalis strains, although the HeLa cell assay indicated that these strains make CDT. PCR experiments indicated the probable presence of cdtB sequences in all of these Campylobacter species. Campylobacter jejuni is established as one of the most frequent bacterial causes of diarrheal disease in humans throughout the world (6, 20, 33). The disease can be variable, but patients typically have watery diarrhea that often contains mucus and may progress to bloody diarrhea (5, 6). Whether specific disease symptoms correlate with specific virulence factors or pathogenic traits is not known. C. jejuni has been reported to produce toxins, although definitive reports of these toxins have not appeared, and it is not clear how many different toxins C. jejuni actually produces (11, 16, 18, 21, 23, 28). Consequently, the role of any toxin in pathogenesis has not been established. Cytolethal distending toxin (CDT) production by C. jejuni was first described by Johnson and Lior (16) in 1988. CDT activity in culture supernatants caused several cultured cell lines, including HeLa and Vero cells, to become slowly distended over a 2-to 4-day period, after which the cells disintegrated. The activity was heat sensitive, trypsin sensitive, and nondialyzable (16). Johnson and Lior screened over 500 C. jejuni isolates obtained from many different countries and found that approximately 41% produced CDT. The CDT-positive isolates included representatives of all four C. jejuni biotypes and numerous serogroups. They also tested C. coli, C. lari, and C. fetus strains and showed that about 42% of these strains produced CDT (16). These Campylobacter species, as well as C. hyointestinalis and C. "upsaliensis," have all been shown to cause diarrheal disease in humans, although they apparently cause the disease much less frequently in the United States than C. jejuni does (8, 10, 26, 32, 33, 37). Johnson and Lior (13-15) also report...

The MHC of cattle encodes two distinct isotypes of class II molecules, DR and DQ. Unlike humans, cattle lack the DP locus and about half the common haplotypes express duplicated DQ genes. The number and frequency of DQA and DQB alleles means that most cattle are heterozygous. If inter- and/or intrahaplotype pairing of DQA and DQB molecules occurs, cattle carrying DQ-duplicated haplotypes may express more restriction elements than would be predicted by the number of expressed alleles. We are investigating whether duplicated haplotypes cause differences in immune response, particularly in terms of generating protective immunity. We have analyzed the Ag-presenting function of DQ molecules in two heterozygous animals, one of which carries a duplicated haplotype. We compared the class II isotype specificity of T cell clones recognizing a putative vaccinal peptide from foot-and-mouth disease virus (FMDV15). We show for the first time that bovine T cells can recognize Ag in the context of DQ molecules. We also present evidence that interhaplotype pairings of DQA and DQB molecules form functional restriction elements. Both animals showed distinct biases to usage of particular restriction elements. Mainly DQ-restricted clones were derived from the animal with duplicated DQ genes, whereas the majority of clones from the animal with a single DQ gene pair were DR restricted. Furthermore, haplotype bias was observed with both animals. These experiments show that understanding of class II chain pairing in addition to knowledge of the genotype may be important in vaccine design where effective epitope selection is essential.

SUMMARYA major feature of the pathology induced by Theileria annulata is acute lymphocytic proliferation, and this study investigates the mechanisms underlying the intrinsic ability of T. anniilata-infecXed monocyles to induce naive autoiogous T cells to proliferate. Different 7". aiinulata-'mkcted clones expressed different but constant levels of MHC class II, varying from < 10 x 10' to 1-5 x 10niolecules/celK as measured by saturation binding. However, no correlation was found between the level of MHC class IT expression and levels of induced T ceil proliferation. Theileria animtatainfected cell lines and clones were assayed for cytokine mRNA expression by reverse transcriplionpolymerase chain reaction (RT-PCR). The infected cells assayed produced mRNA specific for IL-la. \L-\fi. lL-6, IL-10 and tumour necrosis factor-alpha (TNF-a). but not IL-2 or lL-4. One clone (clone G)did not produce mRNA for TNF-f>. The degree of Tcell proliferation induced by infected cells was directly correlated with the amount of mRNA produced for the T cell stimulatory cytokines IL-la and IL-6, as assessed by a semiquantitative technique. In contrast, cells infected with the related parasite T. parva produced mRNA for IL-la, IL-2, IL-4, IL-IO and interferon-gamma (IFN-7). Since T. /5(^/rv«-infected cells also induce naive autologous T cell proliferation, it seems likely that the production oflL-Ifi by cells infected with either parasite is a major signal for the induction of non-specific T cell proliferation.

The BoLA (bovine lymphocyte antigen) Nomenclature Committee met during the 1994 and 1996 conferences of the International Society for Animal Genetics to define a sequence‐based nomenclature system for genes of the BoLA system. The rules for acceptance of new sequences are described and names are assigned to the sequenced alleles of the class II genes DRA, DRB1, DRB2, DRB3, DQA, DQB, DYA, DIB, DMA and DMB. The assignment of BoLA class I sequences to loci will be considered at a later workshop when further sequencing/mapping data are available.

Protection of cattle from alcelaphine herpesvirus-1 (AlHV-1)-induced malignant catarrhal fever (MCF) has been described previously, using an attenuated virus vaccine in an unlicensed adjuvant. The vaccine was hypothesised to induce a protective barrier of virus-neutralising antibody in the oro-nasal region, supported by the observation of high titre neutralising antibodies in nasal secretions of protected animals. Here we describe further analysis of this vaccine strategy, studying the effectiveness of the vaccine formulated with a licensed adjuvant; the duration of immunity induced; and the virus-specific antibody responses in plasma and nasal secretions. The results presented here show that the attenuated AlHV-1 vaccine in a licensed adjuvant protected cattle from fatal intranasal challenge with pathogenic AlHV-1 at three or six months. In addition, animals protected from MCF had significantly higher initial anti-viral antibody titres than animals that succumbed to disease; and these antibody titres remained relatively stable after challenge, while titres in vaccinated animals with MCF increased significantly prior to the onset of clinical disease. These data support the view that a mucosal barrier of neutralising antibody blocks infection of vaccinated animals and suggests that the magnitude of the initial response may correlate with long-term protection. Interestingly, the high titre virus-neutralising antibody responses seen in animals that succumbed to MCF after vaccination were not protective.

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Livestock abortion is an important cause of productivity losses worldwide and many infectious causes of abortion are zoonotic pathogens that impact on human health. Little is known about the relative importance of infectious causes of livestock abortion in Africa, including in subsistence farming communities that are critically dependent on livestock for food, income, and wellbeing. We conducted a prospective cohort study of livestock abortion, supported by cross-sectional serosurveillance, to determine aetiologies of livestock abortions in livestock in Tanzania. This approach generated several important findings including detection of a Rift Valley fever virus outbreak in cattle; high prevalence of C. burnetii infection in livestock; and the first report of Neospora caninum, Toxoplasma gondii, and pestiviruses associated with livestock abortion in Tanzania. Our approach provides a model for abortion surveillance in resource-limited settings. Our findings add substantially to current knowledge in sub-Saharan Africa, providing important evidence from which to prioritise disease interventions.

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