Fig 1.

Overview of the initial events of M. avium subsp. paratuberculosis (MAP) infection. Shown are intestinal enterocytes and an M cell with the basolateral invagination. M. avium subsp. paratuberculosis interacts with the M cell through a fibronectin bridge. The bacteria (blue) are easily trafficked through the M cells, where they can be picked up by dendritic cells (purple) or macrophages (white) and carried to the mesenteric lymph nodes or other regional lymph nodes. In the enterocyte, the bacteria are taken up through the Cdc42-RhoA mechanism into an endosomal vacuole that becomes acidified (red-shaded vacuole). This signals IL-1β production and draws subepithelial macrophages. M. avium subsp. paratuberculosis disrupts cell communication pathways that loosen tight junctions, and thus the pathogen may also slip between enterocytes to gain access to the lamina propria (bottom half of figure). Epithelial cell nuclei are shown in green.