M. tuberculosis PknD is sufficient to trigger adhesion to HBMEC. A and B. Fluorescent microspheres were coated with either PknD sensor or BSA, inoculated into HBMEC, washed, and stained for actin. Confocal microscopy demonstrated that PknD sensor-coated microspheres (panel B) adhere to brain endothelia to a greater degree than those coated with BSA (panel A). C. Confocal images were assembled into a 3D reconstruction and examined under higher magnification. PknD sensor-coated microspheres appear to be largely enveloped by actin processes (arrows) indicating that PknD-induced uptake by host cells may be an active process. D. When confocal images are examined in multiple planes, it is clear that a number of microspheres exist intracellularly. E. Wells containing endothelial cells with microspheres were analyzed for fluorescence. Quantification of fluorescence demonstrated a significant increase in the adherence of PknD-coated microspheres to the monolayer (P = 0.0002). F. Microspheres were pre-incubated with either custom anti-PknD serum or naïve serum. Incubation with anti-PknD serum (1:250 dilution) significantly reduced adherence of PknD (P = 0.0007) but not BSA-coated microspheres (P = 0.6). Moreover, no reduction in adherence was noted for PknD or BSA-coated microspheres when incubated with naïve antiserum (BSA: P = 0.4; PknD: P = 0.1; ANOVA single factor). Fluorescence readings are presented as mean ± standard deviation. *Statistically significant difference.