Viable Mycoplasma mycoides ssp. mycoides Small Colony-Mediated Depression of the Bovine Cell Responsiveness to the Mitogen Concanavalin A

Minimal Bacterial Cell JCVI-syn3B as a Chassis to Investigate Interactions between Bacteria and Mammalian Cells

Mycoplasmas are atypical bacteria with small genomes that necessitate colonization of their respective animal or plant hosts as obligate parasites, whether as pathogens, or commensals. Some can grow axenically in specialized complex media yet show only host-cell-dependent growth in cell culture, where they can survive chronically and often through interactions involving surface colonization or internalization. To develop a mycoplasma-based system to identify genes mediating such interactions, we exploited genetically tractable strains of the goat pathogen Mycoplasma mycoides (Mmc) with synthetic designer genomes representing the complete natural organism (minus virulence factors; JCVI-syn1.0) or its reduced counterpart (JCVI-syn3B) containing only those genes supporting axenic growth. By measuring growth of surviving organisms, physical association with cultured human cells (HEK-293T, HeLa), and induction of phagocytosis by human myeloid cells (dHL-60), we determined that JCVI-syn1.0 contained a set of eight genes (MMSYN1-0179 to MMSYN1-0186, dispensable for axenic growth) conferring survival, attachment, and phagocytosis phenotypes. JCVI-syn3B lacked these phenotypes, but insertion of these genes restored cell attachment and phagocytosis, although not survival. These results indicate that JCVI-syn3B may be a powerful living platform to analyze the role of specific gene sets, from any organism, on the interaction with diverse mammalian cells in culture.

Mycoplasma bovis isolates recovered from cattle and bison (Bison bison) show differential in vitro effects on PBMC proliferation, alveolar macrophage apoptosis and invasion of epithelial and immune cells

In the last few years, several outbreaks of pneumonia, systemically disseminated infection, and high mortality associated with Mycoplasma bovis (M. bovis) in North American bison (Bison bison) have been reported in Alberta, Manitoba, Saskatchewan, Nebraska, New Mexico, Montana, North Dakota, and Kansas. M. bovis causes Chronic Pneumonia and Polyarthritis Syndrome (CPPS) in young, stressed calves in intensively-managed feedlots. M. bovis is not classified as a primary pathogen in cattle, but in bison it appears to be a primary causative agent with rapid progression of disease with fatal outcomes and an average 20% mature herd mortality. Thus, there is a possibility that M. bovis isolates from cattle and bison differ in their pathogenicity. Hence, we decided to compare selected cattle isolates to several bison isolates obtained from clinical cases. We show differences in modulation of PBMC proliferation, invasion of trachea and lung epithelial cells, along with modulation of apoptosis and survival in alveolar macrophages. We concluded that some bison isolates showed less inhibition of cattle and bison PBMC proliferation, were not able to suppress alveolar macrophage apoptosis as efficiently as cattle isolates, and were more or less invasive than the cattle isolate in various cells. These findings provide evidence about the differential properties of M. bovis isolated from the two species and has helped in the selection of bison isolates for genomic sequencing.

Whole Blood Transcriptome Analysis of Mycoplasma mycoides Subsp. mycoides-Infected Cattle Confirms Immunosuppression but Does Not Reflect Local Inflammation

Contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides (Mmm), is a severe respiratory disease of cattle responsible for major economic losses in sub-Saharan Africa. Disease control relies mainly on the use of empirically attenuated vaccines that provide limited protection. Thus, understanding the virulence mechanisms used by Mmm as well as the role of the host immune system in disease development, persistence, and control is a prerequisite for the development of new, rationally designed control strategies. The aim of this study was to assess the use of whole blood transcriptome analysis to study cattle-Mmm interactions, starting by the characterization of the bovine response to Mmm infection during the acute form of the disease. For that purpose, we compared the transcriptome profile of whole blood from six cattle, before challenge by contact with Mmm-infected animals and at the appearance of first clinical signs, using a bovine microarray. Functional analysis revealed that 680 annotated genes were differentially expressed, with an overwhelming majority of down-regulated genes characterizing an immunosuppression. The main bio-functions affected were "organismal survival", "cellular development, morphology and functions" and "cell-to cell signaling and interactions". These affected functions were consistent with the results of previous in vitro immunological studies. However, microarray and qPCR validation results did not highlight pro-inflammatory molecules (such as TNFα, TLR2, IL-12B and IL-6), whereas inflammation is one of the most characteristic traits of acute CBPP. This global gene expression pattern may be considered as the result, in blood, of the local pulmonary response and the systemic events occurring during acute CBPP. Nevertheless, to understand the immune events occurring during disease, detailed analyses on the different immune cell subpopulations, either in vivo, at the local site, or in vitro, will be required. Whole blood transcriptome analysis remains an interesting approach for the identification of bio-signatures correlating to recovery and protection, which should facilitate the evaluation and validation of novel vaccine formulations.

Vaccination of cattle with the N terminus of LppQ of Mycoplasma mycoides subsp. mycoides results in type III immune complex disease upon experimental infection

Contagious bovine pleuropneumonia (CBPP) is a serious respiratory disease of cattle caused by Mycoplasma mycoides subsp. mycoides. Current vaccines against CBPP induce short-lived immunity and can cause severe postvaccine reactions. Previous studies have identified the N terminus of the transmembrane lipoprotein Q (LppQ-N') of M. mycoides subsp. mycoides as the major antigen and a possible virulence factor. We therefore immunized cattle with purified recombinant LppQ-N' formulated in Freund's adjuvant and challenged them with M. mycoides subsp. mycoides. Vaccinated animals showed a strong seroconversion to LppQ, but they exhibited significantly enhanced postchallenge glomerulonephritis compared to the placebo group (P = 0.021). Glomerulonephritis was characterized by features that suggested the development of antigen-antibody immune complexes. Clinical signs and gross pathological scores did not significantly differ between vaccinated and placebo groups. These findings reveal for the first time the pathogenesis of enhanced disease as a result of antibodies against LppQ during challenge and also argue against inclusion of LppQ-N' in a future subunit vaccine for CBPP.

Global suppression of mitogen-activated ovine peripheral blood mononuclear cells by surface protein activity from Mycoplasma ovipneumoniae

Mycoplasma ovipneumoniae is associated with chronic non-progressive pneumonia of sheep and goats. As with many other mycoplasmas involved in animal diseases, protective immune responses have not been achieved with vaccines, even though antibody responses can be obtained. This study focuses on characterizing the interaction of M. ovipneumoniae with ovine PBMC using carboxy-fluorescein-succinimidyl-ester (CFSE) loading and flow cytometry to measure lymphoid cell division. M. ovipneumoniae induced a strong in vitro polyclonal suppression of CD4(+), CD8(+), and B blood lymphocyte subsets. The suppressive activity could be destroyed by heating to 60 degrees C, and partially impaired by formalin and binary ethyleneimine treatment that abolished its viability. The activity resided on the surface-exposed membrane protein fraction of the mycoplasma, since mild trypsin treatment not affecting viability was shown to reduce suppressive activity. Trypsin-treated mycoplasma regained suppressive activity once the mycoplasma was allowed to re-synthesize its surface proteins. Implications for the design of vaccines against M. ovipneumoniae are discussed.

Assessment of in vitro interferon-gamma responses from peripheral blood mononuclear cells of cattle infected with Mycoplasma mycoides ssp. mycoides small colony type

Contagious bovine pleuropneumonia (CBPP) is a lung disease caused by the bacterial pathogen Mycoplasma mycoides ssp. mycoides small colony type (MmmSC). It has been spreading due to a number of factors including poor vaccine efficacy and poor sensitivity of current diagnostic tests. The purpose of this study was to assess interferon gamma (IFN-gamma) release after stimulation of peripheral blood mononuclear cells (PBMC) from experimentally infected cattle. PBMC collected from 15 artificially infected animals were incubated with different concentrations of total MmmSC antigen. After 72h of incubation the IFN-gamma release was measured and found to be elevated in 11 animals. We did not observe a correlation between IFN-gamma release of animals with and without pathomorphological gross lesions. Therefore, our data do not confirm a role for CD4 T-lymphocytes in protection, since there is no correlation between IFN-g secretion (supposed to be mainly derived from CD4 T-cells) and disease severity. Additionally, we applied immunocytochemistry on affected lung tissue and detected no build up of T-lymphocytes (CD4 T-cells, CD8 T-cells) but a high presence of myeloid cells.

Contagious bovine pleuropneumonia: a rationale for the development of a mucosal sub-unit vaccine

Contagious bovine pleuropneumonia (CBPP) remains a major cattle disease in Africa with serious socio-economic consequences. Its eradication requires the development of improved vaccines. Knowledge on this disease and its causing agent, Mycoplasma mycoides subsp. mycoides biotype Small Colony (MmmSC), has been progressing significantly in the last years, opening new areas for vaccine design. Advances were achieved in the understanding of the protective immune responses to MmmSC infection and immunopathological mechanisms allowing the pathogen to escape the host immune response. Based on sequencing and genomic studies, some virulence factors and metabolic pathways were unraveled leading to the identification of potential MmmSC vaccine candidates. Based on these findings, this review presents a scientific strategy to design multi-component sub-unit vaccines for mucosal delivery as the most promising approach for efficient long-term protective vaccines to prevent CBPP.