Fig. 8.

The melanization immune response is concentrated in the tracheal tufts. a, b Bright-field image of a dissected larval dorsal abdomen at 4 h (a) and 24 h (b) post-treatment with GFP-E. coli. At 4 h there is little or no visible melanization, whereas at 24 h widespread melanization is observed, including the uptake of melanin by the pericardial cells and an enrichment of melanin deposits in the tracheal tufts. c, d Melanization, as measured by mean pixel optical density (OD), in the periostial regions (1–7) and the left (L) and right (R) tracheal tufts of injured and GFP-E. coli-treated larvae at 4 h (c) and 24 h (d) post-treatment. At 4 h, OD values are similar in injured and E. coli-treated larvae (P = 0.9969), whereas at 24 h mean OD for all pairwise comparisons was significantly higher in infected larvae when compared to injured larvae (P ≤ 0.0079 for all other comparisons). In c and d, whiskers denote the SEM. For a graphical presentation of how the ROIs were constructed, see Additional file 7: Figure S5B. Directional arrows: A anterior, P posterior, L lateral