Abstract
Objective—To characterize the early cellular immune response to Mycobacterium avium subsp paratuberculosis ( MAP) infection and evaluate the development of granulomatous inflammation at the SC injection site in experimentally inoculated calves.
Animals—Forty-eight 4-week-old calves.
Procedure—Calves received an SC injection of MAP strain 19698 (n = 25), sterile saline (0.9% NaCl) solution (20), or a commercial paratuberculosis vaccine (3); the inoculation site tissue and associated draining lymph node were excised at postinoculation day (PID) 0 (n = 36), 7 (14), 14 (6), 21 (8), and 60 (32). Sections of inoculation site tissues were evaluated immunohistochemically for T-cell subsets; lymph node mononuclear cells (LNMCs) were assessed for T-cell surface markers and for intracellular interferon-γ via flow cytometry.
Results—At MAP inoculation sites, calves developed mild, focal granulomatous inflammation by PID 7; by PID 60, areas of inflammation contained macrophages with numerous lymphocytes. Compared with control calves, there was increased antigen-specific LNMC proliferation in MAP- and vaccine- inoculated calves at PID 60, although proliferation among lymphocyte subsets was not significantly different between MAP-inoculated and control calves; in vaccine-inoculated calves, CD4+ T-cells predominated. In MAP-inoculated and control calves, antigenspecific interferon-γ production by LNMCs did not differ significantly; vaccine-inoculated calves had marked interferon-γ expression by CD4+ T-cells.
Conclusions and Clinical Relevance—In calves, SC administration of MAP resulted in granulomatous inflammation at inoculation sites and an antigen-specific T-cell proliferative response. Results suggest that this experimental system can be used to reproducibly generate antigen-specific T-cells during MAP infection for functional analysis. (Am J Vet Res 2005;66:474–482)
