mesenteric lymph nodes: Heifer #13
shows the serosal (outside) surface of the ileum and the adjacent
mesenteric lymph nodes (arrow). Lymph nodes function to trap bacteria
that may penetrate the intestinal wall. In response to M. paratuberculosis
infection in cattle mesenteric lymph nodes often become enlarged.
The tissues in this picture came from an experimentally M. paratuberculosis-infected
heifer (#13). The pattern of diagnostic
tests results for this animal are shown in another photograph.
Moderate enlargement, without caseous necrosis, of the lymph nodes
is evident. From the serosal surface, the ileum appears normal.
The mucosal (internal) surface
is shown in another photograph.