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
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)