The tuberculosis risk posed by infliximab may reflect its combined effects on TNF and IFN- gamma .

The initial host response to Mycobacterium tuberculosis is driven by innate immunity. For this study, we examined the ability of 18 recent clinical isolates and 5 reference strains to survive and replicate in the context of host innate immunity by using whole blood culture. Six healthy tuberculin-negative volunteers served as subjects. H 37 Ra showed the least capacity to replicate of any of the strains tested, decreasing in viability 1.3 log CFU during 72 h of whole blood culture, whereas H 37 Rv increased 0.32 log. Clinical isolates varied greatly in their ability to replicate in blood cells, ranging from ؊0.4 to ؉0.8 log (P < 0.001). Four showed significantly more growth than H 37 Rv, and one showed significantly reduced growth. Host mechanisms for restricting intracellular mycobacterial growth were more effective during the first 24 h of whole blood culture than during the 24-to 72-h period. Certain mycobacterial isolates appeared preferentially able to withstand host defenses during each of these intervals. Although there was relatively more homogeneity among subjects than among strains, one of the six subjects showed a reduced capacity to restrict intracellular mycobacterial growth due to a defect expressed during the first 24 h of culture. Our findings indicate substantial variability in the capacity of clinical tuberculosis isolates to replicate in host cells in the face of innate host immunity.The early events following inhalation by an immunocompetent, mycobacterium-naïve host of droplet nuclei containing viable Mycobacterium tuberculosis are driven by the innate immune system. The resulting influx of neutrophils, macrophages, NK cells, and other cells to the site of infection serves as a stimulus for granuloma formation and acts directly to limit the extent of mycobacterial replication at this early stage of infection. It has been suggested that the efficiency of these early innate responses may help determine whether a latent infection is established and whether that infection ultimately will progress to active disease.Through evolutionary selection, pathogenic mycobacteria have acquired means to evade specific host immune effector mechanisms, presumably including those of the innate response. The propensity of certain M. tuberculosis isolates to cause outbreaks, for example, has been linked to increased virulence in macrophages or mice in association with altered host cytokine expression profiles (2,3,6,8,12). However, even these virulent outbreak-associated isolates cause disease in only a small proportion of infected individuals. Our understanding of the interplay of biologic and genetic diversity in the host and in the mycobacterium is incomplete, in part because current models to examine the early events in mycobacterial pathogenesis have not been well suited to field or epidemiologic human studies.For the present study, we assessed the capacity of mycobacterial strains to survive phagocytosis and replicate in whole blood cultures. This model permits the involvement of neutrophils, as well as mo...

The activity of oral clofazimine against intracellular Mycobacterium tuberculosis was compared to that of ofloxacin in healthy volunteers by the use of whole-blood cultures. Clofazimine was inactive whether it was tested alone or combined with other drugs that are used to treat multidrug-resistant tuberculosis, despite a total dose of 2 g. Kanamycin was the most active drug tested.Multidrug-resistant tuberculosis (MDR TB) poses a growing public health problem. Studies to assess tissue sterilization in MDR TB are particularly long and complex. Members of our laboratory recently described a method for studying the ability of administered chemotherapy to kill intracellular Mycobacterium tuberculosis cells by using whole-blood cultures (14). In patients with drug-sensitive TB, the whole-blood bactericidal activity (WBA) was correlated with two sputum markers of tissue sterilization, the 8-week sputum culture conversion and the serial sputum CFU slope (16). In the present study, the whole-blood model was used to examine the potential role of clofazimine in the treatment of MDR TB.Our subjects consisted of 10 healthy tuberculin-nonreactive volunteers who provided written informed consent according to an Institutional Review Board-approved protocol. They were randomly assigned to receive only ofloxacin (600 mg) or clofazimine (200 mg) daily for 5 days. Pyrazinamide (25 mg/kg of body weight) was added on days 6 to 10. Ethambutol (25 mg/kg) was added on day 10. This schedule permitted the intracellular accumulation of clofazimine, ofloxacin, and pyrazinamide in phagocytic cells. Kanamycin was added to wholeblood cultures at final concentrations of 20 and 10 g/ml in blood specimens at 2 and 6 h postdose, respectively, to mimic blood levels of 40 and 20 g/ml, respectively. Drug addition was delayed 30 min after infection to allow for phagocytosis.WBA was assessed as previously described (5, 14, 16). Briefly, heparinized blood was diluted 1:1 with medium and infected with M. tuberculosis H37Rv. Members of our laboratory previously documented the high efficiency of phagocytosis in whole-blood cultures (Ͼ95%) by examining CFU counts in the liquid and cellular partitions after low-speed sedimentation and by showing the lack of effect of amoxicillin-clavulanate, which does not reach adequate intracellular levels to act against M. tuberculosis (14); this eliminates the need to remove extracellular bacilli. After 72 h of incubation, the host cells were disrupted by hypotonic lysis, and bacilli were sedimented and inoculated into BACTEC medium. Bacillus killing was calculated based on days-to-positivity by using a standard curve. The total bactericidal effect was assessed as the area under the curve (AUC) (16). The results were examined by a paired or unpaired t test.At the baseline, there was a net growth of M. tuberculosis H37Rv of 0.41 log CFU over 72 h in the subjects' blood cells. A single dose of clofazimine had no effect in blood sampled 2 h afterward (mean, 0.42 log CFU; P ϭ 0.3), whereas the corresponding effect of ofloxa...