Abstract
Background
Mycobacterium avium subsp. paratuberculosis infected animals show a variety of granulomatous lesions: from focal forms, restricted to the gut-associated lymphoid tissue (GALT), related to latency and resistance, to diffuse lesions, with abundant (multibacillary) or scant (paucibacillary) bacteria, seen in clinical stages. Factors that determine the response to the infection and responsible for the occurrence of the different types of lesion are still not fully determined. It has been seen that regulatory T cells (Treg) play an important role in the progress of various diseases where they act on the limitation of the immunopathology associated with the immune response. In the case of paratuberculosis (PTB) the role of Treg lymphocytes in the immunity against Map is far away to be completely understood; therefore, several studies addressing this subject have appeared recently. The aim of this work was to assess, by immunohistochemical methods, the presence of Foxp3+ T lymphocytes in intestinal samples with different types of lesions seen in cows with PTB.
Methods
Intestinal samples of twenty cows showing the different pathological forms of PTB were evaluated: uninfected controls (n = 5), focal lesions (n = 5), diffuse paucibacillary (n = 5) and diffuse multibacillary (n = 5) forms. Foxp3+ lymphocyte distribution was assessed by differential cell count in intestinal lamina propria (LP), gut-associated lymphoid tissue (GALT) and mesenteric lymph node (MLN).
Results
A significant increase in the number of Foxp3+ T cells was observed in all infected animals, but this increase was only significant in cows with focal lesions and, to a lesser extent, in animals with diffuse paucibacillary forms. The former showed the highest numbers, significantly different from those found in cows with diffuse lesions, where no differences were noted between the two forms. No specific distribution pattern was observed within the granulomatous lesions in any of the groups.
Conclusions
The increase of Foxp3+ T cells in focal forms, that have been associated with latency or resistance to infection, suggest an anti-inflammatory action of these cells at these stages, helping to prevent exacerbation of the inflammatory response, as occurs in diffuse forms, responsible for the appearance of clinical signs.