FIG. 2.

SP-D increases P-L fusion of M. tuberculosis-containing phagosomes. Duplicate MDM monolayers were loaded with HRP and then incubated with M. tuberculosis in the presence or absence of SP-D. After 2 h at 37°C, the MDMs were fixed and the HRP revealed by diaminobenzidine. The MDMs were then processed for TEM. (A) TEM section showing a single bacillus contained in a phagosome that has not fused with lysosomes. (B) TEM section showing a single bacillus (arrowhead) contained within a phagosome that also contains the characteristic black HRP precipitate (arrow), indicating P-L fusion. (C) Graph showing the summary of percentages of M. tuberculosis phagosomes containing the HRP precipitate with one, two, or three or more bacilli per phagosome. The results shown are the means ± standard deviations of duplicate determinations in a representative experiment (mean ± standard deviation, n = 2, P < 0.05 for the SP-D group versus the control group for one or two bacteria).