Figure 1.

Threshold-dependent macrophage activation during Yersinia infection. Macrophages from Y. pseudotuberculosis (Yptb)-infected mice were assessed for activation by ICAM-1 expression and compared with macrophages from uninfected mice (A). Shown are representative histograms from infected mice, with (right panel) and without (left panel) activated macrophages. Bacterial colonization of infected mice was quantified by plating and plotted as cfu at Days 4–6 postinfection. The presence of activated macrophages is indicated in the accompanying legend (B). Representative results from one of several experiments; data from ref. [20]. MLN, mesenteric lymph nodes.