Immunofluorescence and FESEM examination of human MCETs. MCs were seeded on poly-L-lysine–coated glass slides, stimulated with 25 nM PMA for 10 minutes, then infected with FITC-labeled S pyogenes (MOI 25:1) for 1 hour and fixed with 4% paraformaldehyde. (A) Colocalization of DNA, S pyogenes, and LL-37 in MCETs (bars, 10 μm): (i) Dapi-stained DNA; (ii) FITC-labeled S pyogenes; (iii) immunostaining of LL-37 with Alexa-red–labeled antibodies against human LL-37; and (iv) overlay of A1-3. (B) Immunostaining of MCETs with Alexa-red-labeled antibodies against histones (bar, 10 μm). Insert in the lower-left corner (ii) shows a higher magnification of S pyogenes (green) entrapped in the MCETs (red; bar, 3.5 μm). (C) Immunostaining of MCETs with Alexa-red–labeled antibodies against tryptase. S pyogenes are labeled green and DNA are labeled blue (bar, 8 μm). (D) FESEM image of MCETs produced by human MCs during coculture with S pyogenes. Microorganisms entrapped in the MCETs structures are indicated by white arrows (bar, 5 μm). (E) Higher magnification showing S pyogenes entrapped in the fibers of the MCETs (white arrows; bar, 1 μm).