Inflammatory cell infiltration into muscle tissue. Tissues with injected DNA (bolus and microspheres) were retrieved and sectioned at day 2 (A, C, E) or day 50 (B, D, F). DNA was delivered by bolus injection (A, B), high molecular weight PLG microspheres (C, D), or low molecular weight PLG microspheres (E, F). Labels indicate polymer (P), muscle tissue (M), and inflammatory cells (arrows). The scale bar equals 100 μm.