In vivo transcriptomic profiling of colonic mucosa during Brachyspira hyodysenteriae infection in pigs.

Acute *B. hyodysenteriae* infection in pigs leads to significant immune suppression and mucosal alterations.

This study investigated the in vivo transcriptomic response of colonic mucosa in pigs infected with *Brachyspira hyodysenteriae*, the causative agent of swine dysentery (SD). Sixteen pigs were experimentally infected and divided into two groups: Early_inf (n=8), at the onset of fecal shedding, and Acute_inf (n=8), during the acute clinical phase characterized by mucohemorrhagic diarrhea. In the Early_inf group, no significant changes in gene expression were observed, except for an overexpression of matrix metalloproteinases (MMPs), which may be associated with early ulceration of the colonic epithelium. In contrast, the Acute_inf group exhibited significant upregulation of S100A8, S100A9, and S100A12 genes. Notably, most host biological processes, particularly those related to the immune response, were downregulated, including chemokine and cytokine signaling, as well as immune cell chemotaxis and migration. Cell type predictions indicated a depletion of immune cells, except neutrophils, and an enrichment of stromal cells in the Acute_inf group. Alterations in mucin gene expression were also observed, with overexpression of MUC5AC, MUC20, and GCNT3, a tendency in MUC2, and downregulation of MUC1 and MUC3. These findings provide insights into the pathophysiology of SD, highlighting key aspects of host-pathogen interactions and the host response to *B. hyodysenteriae* infection.

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