Technical advance: monitoring the trafficking of neutrophil granulocytes and monocytes during the course of tissue inflammation by noninvasive 19F MRI.

Inflammation results in the recruitment of neutrophils and monocytes, which is crucial for the healing process. In the present study, we used (19)F MRI to monitor in vivo the infiltration of neutrophils and monocytes from the onset of inflammation to the resolution and healing phase. Matrigel, with or without LPS, was s.c.-implanted into C57BL/6 mice. This resulted in a focal inflammation lasting over a period of 20 days, with constantly decreasing LPS levels in doped matrigel plugs. After i.v. administration of (19)F containing contrast agent, (19)F MRI revealed a zonular (19)F signal in the periphery of LPS containing matrigel plugs, which was not observed in control plugs. Analysis of the (19)F signal over the observation period demonstrated the strongest (19)F signal after 24 h, which decreased to nearly zero after 20 days. The (19)F signal was mirrored by the amount of leukocytes in the matrigel, with neutrophils dominating at early time-points and macrophages at later time-points. Both populations were shown to take up the (19)F contrast agent. In conclusion, (19)F MRI, in combination with the matrigel/LPS model, permits the noninvasive analysis of neutrophil and monocyte infiltration over the complete course of inflammation in vivo.