# Influence of Paratuberculosis Vaccination on the Local Immune Response in Experimentally Infected Calves: An Immunohistochemical Analysis

## TL;DR

This study shows that vaccination with Silirum® boosts the immune response in the intestines of calves infected with paratuberculosis, potentially offering better protection.

## Contribution

The study provides new insights into how Silirum® vaccination influences local immune responses in the intestine and granulomas of infected calves.

## Key findings

- Vaccinated calves with focal lesions showed increased TLR2+ macrophages in the intestine and higher iNOS activity in granulomas.
- Multifocal lesions were associated with reduced intestinal innate immunity and higher anti-inflammatory markers in granulomas.
- Vaccination enhanced TLR2 and IFN-γ expression at the injection-site granuloma.

## Abstract

Vaccination is the most cost-effective method to control paratuberculosis in dairy cattle, but its effects on the local immune response in the intestine are not well understood. This study evaluated the local innate and cell-mediated response in calves vaccinated with Silirum® and subsequently infected with paratuberculosis. Samples were taken from injection-site granuloma, scapular and mesenteric lymph nodes, and the intestine. Results show that vaccinated calves with focal forms controlling the infection displayed a robust innate response at the intestine, with a strong cell-mediated immunity in the granulomas. An upregulated innate and pro-inflammatory response was also observed in the site of the injection. In contrast, animals with progression of the disease with multifocal or diffuse lesions, both vaccinated and not vaccinated, showed weak intestinal innate immunity and an anti-inflammatory response in the granulomas. In summary, vaccination with Silirum® enhances the immune response in the intestine, potentially contributing to protection against paratuberculosis.

Vaccination remains the most cost-effective way to control clinical paratuberculosis in dairy herds, but its effect on the immune response at the intestine have been poorly characterized. The aim of this study was to evaluate the expression of toll-like receptor (TLR)-1, TLR2, TLR4, TLR9, interferon (IFN)-γ, inducible nitric oxide synthase (iNOS) and cluster of differentiation (CD)-204 in calves vaccinated with Silirum® and then experimentally infected with paratuberculosis, using immunohistochemical techniques. Samples of the injection-site granuloma, scapular lymph node, intestine and mesenteric lymph nodes were studied. Lesions were classified as focal, multifocal and diffuse paucibacillary (lymphocytic). The immunolabeling for TLR1, TLR2, TLR4 and IFN-γ was assessed according to the number of immunolabeled cells, while TLR9, iNOS and CD204 immunolabeling in the lesions was evaluated using a histological score (H-score). Vaccinated calves with focal forms showed a significant increase in the number of macrophages immunolabeled TLR2 at the intestine and in the H-score values for iNOS in the granulomas. A greater immunolabeling of TLR2 and IFN-γ was detected at the injection-site granuloma. Animals with multifocal lesions, regardless of the vaccination status, showed lower numbers of TLR2+ macrophages and higher H-score values for CD204 in the granulomas. Thus, the protection conferred by the Silirum® vaccine is associated with an enhanced immunological response in the intestine.