Differential Gene Expression in Porcine Lung Compartments after Experimental Infection with Mycoplasma hyopneumoniae

Abstract

Mycoplasma hyopneumoniae (Mhyo) is a major porcine pathogen worldwide. Understanding its interaction with the pig immune system is crucial for effective disease control. This study evaluates the use of minimal tissue samples from different lung compartments to analyze this interaction in detail, in addition to the microscopic and macroscopic evaluation of lung lesions. Key findings reveal strain-specific virulence variability and a differential cytokine expression in the lung compartments tested, highlighting the relevance of Th1 and Th2, and a potential role for Th17-mediated immune responses in Mhyo infection. The data analyzed shed light on the complex nature of Mhyo infection and its interplay with the pig's immune system, potentially aiding in the development of better disease management strategies. Mycoplasma hyopneumoniae (Mhyo) is the causative agent of porcine enzootic pneumonia (EP), as well as one of the main pathogens involved in the porcine respiratory disease complex. The host-pathogen interaction between Mhyo and infected pigs is complex and not completely understood; however, improving the understanding of these intricacies is essential for the development of effective control strategies of EP. In order to improve our knowledge about this interaction, laser-capture microdissection was used to collect bronchi, bronchi-associated lymphoid tissue, and lung parenchyma from animals infected with different strains of Mhyo, and mRNA expression levels of different molecules involved in Mhyo infection (ICAM1, IL-8, IL-10, IL-23, IFN-alpha, IFN-gamma, TGF-beta, and TNF-alpha) were analyzed by qPCR. In addition, the quantification of Mhyo load in the different lung compartments and the scoring of macroscopic and microscopic lung lesions were also performed. Strain-associated differences in virulence were observed, as well as the presence of significant differences in expression levels of cytokines among lung compartments. IL-8 and IL-10 presented the highest upregulation, with limited differences between strains and lung compartments. IFN-alpha was strongly downregulated in BALT, implying a relevant role for this cytokine in the immunomodulation associated with Mhyo infections. IL-23 was also upregulated in all lung compartments, suggesting the potential involvement of a Th17-mediated immune response in Mhyo infections. Our findings highlight the relevance of Th1 and Th2 immune response in cases of EP, shedding light on the gene expression levels of key cytokines in the lung of pigs at a microscopic level.