FIG. 1.

N. meningitidis internalization fails to induce macrophage apoptosis. (A) MDM were infected with nonopsonized (Op−) or opsonized (Op+) N. meningitidis strain MC58, and at 4 or 20 h postinfection, the cell density was assessed and normalized to that of mock-infected (MI) cells (n = 6). (B) Percentage of terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeled MDM after mock infection or infection with opsonized MC58 or S. pneumoniae (Spn), used as a control for MDM apoptosis. Data are means + SEM (n = 3). The positive control (DNase I treated) was set to 100%, and the negative control was set to 0% per the manufacturer's instructions. (C) Levels of apoptosis, as assessed by nuclear morphology after 4′,6′-diamidino-2-phenylindole (DAPI) staining, in MDM 4 or 20 h after mock infection or infection with an N. meningitidis strain lacking porB or the parental strain H44/76 (n = 4). The positive control (pneumococcal infection) value was 19.1 ± 0.9%. (D) Levels of apoptosis, as assessed by nuclear morphology after DAPI staining, in U937 cells, differentiated with 10 ng/ml phorbol 12-myristate 13-acetate (Sigma-Aldrich) for 3 days to produce adherent cells, 20 h after mock infection or infection with the porB mutant or H44/76 (n = 4). The positive control (pneumococcal infection) value was 18 ± 0.6%.