Ever wondered what it looks like in your finger, say, when you get a splinter and your immune system leaps into action?  Of course you have.

This amazing movie (double-click to play, I think) shows neutrophils (in green) responding to the presence of either a parasite (Leishmania major; in red) or to simple artificial beads (in blue), injected into the ear of a mouse. Neutrophils react to both  foreign materials by galloping to the site and swarming the target.  Neutrophils are a part of the rapid-response innate immune system, and this movie shows the first five hours of the response.

4-dimensional image series from the ear pinna of a LYS-eGFP mouse in which blue fluorescent beads and L. major had been deposited adjacent to one another in the skin of the same ear. eGFP-expressing cells are shown in green, L. major-RFP is shown in red, and beads are shown in blue. Playback speed is 1200x. Scale bar, 200?m

N. C. Peters, J. G. Egen, N. Secundino, A. Debrabant, N. Kimblin, S. Kamhawi, P. Lawyer, M. P. Fay, R. N. Germain, D. Sacks (2008). In Vivo Imaging Reveals an Essential Role for Neutrophils in Leishmaniasis Transmitted by Sand Flies Science, 321 (5891), 970-974 DOI: 10.1126/science.1159194