TABLE 1.

Uptake of M. tuberculosis by human monocyte-derived macrophages following exposure to different pHs

Time of exposure to acid (h)aUptake (% of initial inoculum) of M. tuberculosis at pH:Uptake (%) at pH 6 withb:
5.06.07.28.0Serum (10%)No serum
120 ± 423 ± 617 ± 615 ± 8NDND
247 ± 6c49 ± 5c19 ± 416 ± 5NDND
457 ± 14c59 ± 7c18 ± 620 ± 448 ± 549 ± 3
2451 ± 9c48 ± 7c19 ± 520 ± 6NDND
  • a M. tuberculosis H37Rv in 7H9 broth was exposed to different conditions for 1, 2, 4, and 24 h. After exposure, the bacteria were centrifuged at 4°C and resuspended in RPMI 1640 with 10% heat-inactivated autologous serum, and the concentration was adjusted to 5 × 106 bacteria/ml (multiplicity of infection [MOI] of 10). Phagocytosis was carried out for 1 h. Results using an MOI of 1 were similar and are not shown. The experiment was repeated four times. Results are means ± standard deviations.

  • b Bacteria (5 × 106) were incubated at pH 6 for 4 h prior to the assay. Then, bacteria were washed at 4°C and incubated with macrophages in the absence or presence of 10% autologous serum or were heat inactivated for 1 h. The uptake of bacteria cultured under laboratory conditions by macrophages increased from 16% ± 3% to 24% ± 4% of the inoculum (P < 0.05). ND, Not done.

  • c P < 0.05 compared with uptake of M. tuberculosis incubated at pH 7.2 for the same period of time.