Cytokeratin expression and distribution pattern of epithelioid macrophages in granulomatous lesions of animals with different pathological forms of bovine paratuberculosis: cytokeratin as a biomarker of resilience.

Abstract A recent genome-wide association study identified 92 genetic variants in cattle with paratuberculosis (PTB)-associated multifocal lesions. Pathway analysis with the identified candidate genes revealed a significant enrichment of the keratinization (KRT) pathway in those animals. To confirm, at the protein level, this enrichment the number and distribution pattern of cytokeratin (CK)-expressing cells in granulomas of distal jejunum (DJE) and jejunal lymph nodes (JELN) of animals with different PTB-associated lesions (focal, multifocal and diffuse) and in control animals without lesions was determined by quantitative double-immunohistochemical analysis using Iba1 (ionized calcium-binding adapter molecule-1) and CK as specific markers of macrophages and epithelial cells, respectively. Animals with multifocal lesions showed the highest numbers of double-Iba1/CK positive cells (epithelioid macrophages (EMs)) showing significant differences with focal, diffuse and control animals in JELN and higher numbers of single-CK expressing cells in JELN and DJE. Two distribution patterns of the EMs in the granulomas were observed. In focal and multifocal animals EMs were surrounding the granuloma forming a barrier crucial to control Map infection while in animals with diffuse lesions (with significantly higher infection scores) EMs were throughout all the extension of the granuloma. Multifocal animals might be resilient to the disease as they control the shift from subclinical to the clinical through formation of ordered granulomas where EMs have a relevant role preventing Map dissemination and maintaining tissue integrity. Since CK expression was enriched in cattle with multifocal lesions, it could be considered as a potential biomarker of PTB resilience.