AUTHOR=Park Kun Taek , Allen Andrew J. , Barrington George M. , Davis William C. 

TITLE=Deletion of relA abrogates the capacity of Mycobacterium avium paratuberculosis to establish an infection in calves

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=4

YEAR=2014

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2014.00064

DOI=10.3389/fcimb.2014.00064

ISSN=2235-2988

ABSTRACT=<p>Previous comparative studies in goats revealed deletion of <italic>relA</italic> but not <italic>pknG</italic> abrogates the capacity of <italic>Mycobacterium avium</italic> subsp. <italic>paratuberculosis</italic> (<italic>Map</italic>) to establish a persistent infection. The immune response elicited by the mutant cleared infection. The objective of the present study was to extend the studies in calves and compare the proliferative response elicited by the <italic>relA</italic> deletion mutant (Δ<italic>relA</italic>) and <italic>Map</italic> using flow cytometry and quantitative reverse transcription real-time PCR (qRT-PCR). Six 3-day-old calves were divided into two groups. Three were vaccinated with Δ<italic>relA</italic> and 3 inoculated with wild type <italic>Map</italic>. The calves were challenged with <italic>Map</italic> 1 month later and necropsied 3 months post challenge. Three untreated calves were used as uninfected controls. Examination of tissues revealed the Δ<italic>relA</italic> mutant was immune eliminated. Bacterial load of <italic>Map</italic> was significantly reduced in the calves vaccinated with Δ<italic>relA</italic> and challenged with <italic>Map</italic> in comparison with calves inoculated and challenged with <italic>Map</italic>. A vigorous CD4 memory T cell response was detected at necropsy in PBMC from both infected groups. CD8 positive NK cells proliferated in the presence and absence of antigen stimulation in both treated groups but not in the uninfected group. IFN-γ, IL17, and IL22 gene expression were up-regulated with an associated increase in their transcription factors, Tbet and RORC, in both treated groups. TGF-β, IL-10, and FoxP3 were not up-regulated, indicating no activation of regulatory T cells. The findings show that the immune response to Δ<italic>relA</italic> is clearly different than the response to <italic>Map</italic>. Understanding the immunological basis for this difference should facilitate development of a vaccine that elicits sterile immunity.</p>