Production and utilization of interleukin-15 in malignant catarrhal fever.

Malignant catarrhal fever (MCF) is an often fatal lymphoproliferative disease of ungulates caused by either alcelaphine herpesvirus-1 (AlHV-1) or ovine herpesvirus-2 (OvHV-2). The pathogenesis of MCF is poorly understood, but appears to involve an auto-destructive pathology whereby cytotoxic lymphocytes destroy areas of a variety of tissues. The cytokine interleukin-15 (IL-15) is involved in the development and maintenance of cytotoxic lymphocytes and may therefore have a role in the pathogenesis of MCF. Virus-infected large granular lymphocytes (LGLs) were obtained from the tissues of rabbits infected with AlHV-1 or OvHV-2. These cells exhibited a similar proliferative response to IL-15 and to IL-2 in culture, but their content of the activated cytotoxic enzyme (BLT-esterase) was maintained at higher levels in the presence of IL-15 compared with IL-2. The LGLs did not express IL-15 mRNA or produce IL-15 protein. By contrast, there was abundant expression of IL-15 mRNA and protein in affected tissues. IL-15 production was associated with necrotic lesions of the mesenteric lymph node and appendix of OvHV-2-infected rabbits, but was not found in the same tissues of rabbits infected with AlHV-1 in which there were no necrotic lesions. The cellular source of the IL-15 was predominantly lymphoid cells that did not express B cell or monocyte-macrophage markers. Only a few IL-15+ cells (<10%) co-localized with pan-T cells or CD8+ T cells. The abundance of IL-15 in tissue with lesions of MCF suggests that this cytokine may have a role in the pathogenesis of MCF.

Immunohistochemical study of experimental malignant catarrhal fever in rabbits.

Malignant catarrhal fever (MCF) is an often-fatal lymphoproliferative disease of a variety of ungulates that occurs worldwide. It is caused by either of the highly related but distinct gammaherpesviruses alcelaphine herpesvirus-1 (AlHV-1, wildebeest reservoir) or ovine herpesvirus-2 (OvHV-2, sheep reservoir). MCF in rabbits is an excellent model as it closely resembles the disease in susceptible ungulates that include cattle, deer and bison. In this study, newly available and previously characterized monoclonal antibodies specific for rabbit leucocyte differentiation molecules were used to perform a detailed immunohistochemical examination of both AlHV-1 MCF and OvHV-2 MCF in rabbits. Differences in the MCF caused by the two viruses included: less tissue necrosis and more lymphoid cell accumulations in AlHV-1 MCF compared with OvHV-2 MCF, and in particular marked tissue necrosis in the mesenteric lymph node, appendix and liver of OvHV-2-infected animals when compared with either other tissues in OvHV-2 MCF or AlHV-1 MCF lesions in any tissue. In both AlHV-1 MCF and OvHV-2 MCF, lymphoid cell accumulations in lymphoid and non-lymphoid tissues consisted mainly of T-cells with a corresponding absence of B-cells. CD8(+) T-cells accounted for a proportion of these in the non-lymphoid tissues, but there was evidence for the accumulation of an unidentified T-cell subset/subsets as well. This study extends our understanding of the mechanisms of immuno-pathogenesis of MCF.

Ovine chlamydial abortion: characterization of the inflammatory immune response in placental tissues.

Ovine chlamydial abortion is a serious cause of fetal mortality in several sheep-rearing countries. The causal agent, Chlamydophila abortus (Chlamydia psittaci), does not generally induce clinical signs in the ewe other than abortion; this is associated with macroscopically visible damage in the placenta, which may be inflamed and thickened. To investigate the nature of the placental inflammation, seven pregnant sheep were inoculated subcutaneously at 70 days' gestation with C. abortus (strain S 26/3). A further five pregnant sheep received control inoculum by the same route at the same stage of pregnancy. Three of the infected ewes produced stillborn lambs and four produced live lambs. Lesions characteristic of chlamydial infection were present in all placentas except for two from one ewe that gave birth to twins. Histopathological examination of placental tissues from aborted fetuses showed a mixed inflammatory cell infiltrate with vasculitis and thrombosis in the mesenchyme of the intercotyledonary membranes. Cells expressing the macrophage-associated molecule CD 14 were found to be numerous, as were cells expressing major histocompatibility complex class II (MHC II) molecules. Many cells expressing messenger RNA (mRNA) encoding for tumour necrosis factor-alpha (TNF-alpha) were demonstrated, but few cells expressing interferon gamma mRNA and none expressing interleukin-4 mRNA were detected. The fetal immune response included small numbers of CD4+ and CD8+ cells, gamma delta T cells and B cells. It is concluded that abortion is the result of several factors, including destruction of tissue by C. abortus, vascular thrombosis, and an inflammatory response by the fetus. Production of TNF-alpha by fetal macrophages expressing MHC II molecules may be of considerable significance in the pathogenesis of abortion.

Detection of cellular cytokine mRNA expression during orf virus infection in sheep: differential interferon-gamma mRNA expression by cells in primary versus reinfection skin lesions.

In sheep infected with the parapoxvirus orf virus, primary infection orf skin lesions developed and resolved within 8 weeks. Reinfection lesions were smaller and resolved within 3 weeks. The host response in the skin was characterized by an accumulation of neutrophils, dendritic cells, CD4+ T cells, CD8+ T cells, B cells and T19+ gammadelta T cells. The magnitude of this accumulation paralleled orf virus replication in the skin. In situ hybridization was used to detect cells expressing interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) and interleukin-4 (IL-4) mRNAs in orf skin. Cells expressing IL-4 mRNA were not detected at any time after infection. Cells expressing IFN-gamma mRNA were detected after reinfection but not after primary infection. Cells expressing TNF-alpha mRNA included epidermal cells, vascular endothelium and uncharacterized cells that increased more rapidly in the skin after reinfection compared to primary infection. The results are consistent with a prominent role for IFN-gamma in the host immune response controlling the severity of the disease.

Analyses of the genomes of chlamydial isolates from ruminants and pigs support the adoption of the new species Chlamydia pecorum.

Analysis of the genomic DNAs of chlamydial isolates from sheep, cattle, and pigs was performed by Southern blot hybridization and by restriction endonuclease (RE) profiling of DNA amplified by PCR. The hybridization probes were derived from whole genomic DNA, the major outer membrane protein (MOMP) gene, the 16S rRNA gene, and an avian Chlamydia psittaci isolate plasmid. The PCR analysis used targets in the MOMP gene, the 16S rRNA gene, and the 60-kDa cysteine-rich protein gene. Together, the results showed that although there was considerable heterogeneity in the DNA sequence in the MOMP gene region, all the isolates had the same underlying total genomic RE profiles and yielded identical RE profiles for the rRNA and 60-kDa-protein gene regions. Most of the isolates were found to hybridize with the plasmid probe. Comparison of the MOMP sequence of one of the isolates (P787) with that of a known Chlamydia pecorum strain together with the results of the RE analyses allowed the conclusion that the isolates should all be classified within this new species.

Efficacy trials with tissue-culture grown, inactivated vaccines against chlamydial abortion in sheep.

Vaccines containing inactivated, semi-purified antigen of ovine abortifacient Chlamydia psittaci were prepared from tissue-culture grown harvests of two strains. These were evaluated for efficacy against experimentally reproduced enzootic abortion of ewes (EAE), the protection index (PI) of each vaccine being calculated from three variables. Trial 1 tested the adjuvants Marcol 52/Arlacel A, ISCOM matrix, Novasomes and Alhydrogel, each administered with a total antigen dose of 4 micrograms chlamydial protein (cp), against challenge with the two homologous vaccine strains. The first three formulations yielded PIs of 39-42%, while that of Alhydrogel was 23%. Marked granuloma and/or abscess formation occurred in the Marcol 52/Arlacel A group but in none of the others, and only this group seroconverted following vaccination. In Trial 2, ISCOM matrix containing 16 micrograms cp per dose was administered once or twice. Two challenges were used, one involving the two vaccine strains and the other these two strains plus five others, but no significant differences were seen between them. The double dose schedule, which was better than the single dose and also several Novasomes formulations tested concurrently, gave PIs of 64 and 77% against the two challenges (combined value 71.5%). Trial 3 studied duration of immunity over two lambing seasons using three different administration schedules of 16 micrograms cp in ISCOM matrix, namely single dose in year 1, single dose in year 2 (Group 1), double dose then booster (Group 2), and double dose without booster (Group 3). PIs against the homologous bivalent challenge were 79-80% for Groups 1 and 3 and 91% for Group 2.(ABSTRACT TRUNCATED AT 250 WORDS)