Three scenarios for signal propagation from the site of infection. Three scenarios for signal propagation from the site of infection marked by the black circle. Cells are aligned vertically and changes of chemoattractant concentrations in time are developing from left to right. The blue (red) encode low (high) concentrations of chemoattractant (T). White lines represent trajectories of neutrophils chemotaxing from blood vessels (dashed lines). The trajectories were calculated using a "Local Excitation - Global Inhibition" model, described in the additional file 1. In A) the chemoattractant is diffusing from the site of infection. The signal is short-ranged, and no neutrophils are recruited from the distant blood vessels. In both B) and C) the signal is long-ranged. In B) the diffusing chemoattractant is continuously amplified by tissue cells. The gradient is sharp at the blood vessel but it disappears deeper in the tissue thus leaving neutrophils devoid of direction. In C) diffusing chemoattractant is amplified transiently. The waves recruit neutrophils from the blood stream and also serve as a directing signal for the neutrophils that are already in the tissue.