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

From:
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