FIG. 3.

Efavirenz distribution in the macaque colon. Frozen cross-sections of colon were thaw mounted and analyzed by MSI according to Thompson et al.^.61 (A) Using high-resolving power mass spectrometry, on-tissue response to efavirenz (inset) can be sensitively discriminated from the complex endogenous response in each measured mass spectrum. (B) The resulting MSI of efavirenz in a cross-section is shown on the left, with adjacent CD3⁺ T cell staining of a serial tissue slice on the right. MSI signal intensity is shown next to the image on a concentration-dependent scale. The bottom of the scale (0) represents no efavirenz present, whereas the top of the scale is set to the highest per-voxel efavirenz signal observed. Brighter colors represent higher efavirenz concentrations. Efavirenz is found at higher concentrations in areas of the lamina associated with CD3⁺ T cell staining. Image credit: Rosen E and Kashuba A. MSI, mass spectrometry imaging.