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 systemin 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 TNF alpha, 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

Use of fluorescence expression tools for the comparative analysis of the interactions of Mycoplasma mycoides and Mycoplasma bovis with bovine cells

Background: Fluorescence expression systems adapted to the analysis of host-mycoplasma interactions were recently developed. The aim of this work was to apply them to study the colonisation and persistence capabilities of the bovine pathogens Mycoplasma mycoides subsp. mycoides (Mmm) and Mycoplasma bovis in bovine cells. Methods. Mini-transposons affording high-level expression of GFP2, mCherry, mKO2 and mNeonGreen were used to mark Mmm and M. bovis strains. The resulting fluorescent mutants were characterised by epifluorescence microscopy and fluorimetry and the sites of transposon insertion were identified by sequencing. Interactions of mNeonGreen mutants with bovine cells were analysed using flow cytometry and confocal microscopy. Results: The production, selection and characterisation of fluorescent clones were straightforward and compatible with the production of fluorescent mutant banks. M. bovis presented much higher adhesion, invasion and proliferation capacities than Mmm in culture with non-phagocytic cells and showed increased resistance to elimination by macrophages. Conclusion: The remarkable differences in the invasion and persistence capabilities of Mmm and M. bovis observed here are in agreement with the pathogenesis of the infections caused by these mycoplasmas. mNeonGreen fluorescent mutants have proven extremely useful for analysis of mycoplasma-host cell interactions. Furthermore, the fluorescence expression tools used in this study offer innumerable perspectives for the functional analysis of a wide range of mycoplasma species both in vitro and in vivo

Pulmonary and Serum Antibody Responses Elicited in Zebu Cattle Experimentally Infected with Mycoplasma mycoides Subsp. mycoides SC by Contact Exposure

The purpose of the present study was to characterize the Mycoplasma mycoides subsp. mycoides small colony (MmmSC)-specific humoral immune response at both systemic and local levels in cattle experimentally infected with MmmSC, for a better understanding of the protective immune mechanisms against the disease. The disease was experimentally reproduced in zebu cattle by contact. Clinical signs, postmortem and microbiological findings were used to evaluate the degree of infection. Serum and bronchial lavage fluids (BAL) were collected sequentially, before contact and over a period of one year after contact. The kinetics of the different antibody isotypes to MmmSC was established. Based on the severity of the clinical signs, post mortem and microbiological findings, the animals were classified into three groups as acute form with deaths, sub-acute to chronic form and resistant animals. Seroconversion was never observed for the control animals throughout the duration of the experiment, nor for those classified as resistant. Instead, seroconversion was measured for all other cattle either with acute or sub-acute to chronic forms of the disease. For these animals, IgM, IgG1, IgG2 and IgA responses were detected in the serum and BAL samples. The kinetics of the IgM, IgG1 and IgG2 responses was nearly similar between both groups of animals. No evident correlation could thus be established between the levels of these isotypes and the severity of the disease. Levels of IgA were high in both BAL and serum samples of animals with sub-acute to chronic forms of the disease, and tended to persist throughout the entire experimental period. In contrast, animals with acute forms of the disease showed low levels of IgA in their BAL samples with none or very transient but low levels of IgA in the serum samples. Our results thus demonstrated that IgA is produced locally in MmmSC experimentally infected cattle by contact and may play a role in protection against contagious bovine pleuropneumonia