TNF-α Controls Intracellular Mycobacterial Growth by Both Inducible Nitric Oxide Synthase-Dependent and Inducible Nitric Oxide Synthase-Independent Pathways

Abstract

The role of TNF-α in the control of mycobacterial growth in murine macrophages was studied in vitro. Infection of macrophages from TNF-α gene disrupted (TNF-knockout (KO)) mice with recombinant Mycobacterium bovis bacillus Calmette Guérin (BCG) expressing the vector only (BCG-vector) resulted in logarithmic growth of the intracellular bacilli. Infection with BCG-secreting murine TNF-α (BCG-TNF) led to bacillary killing. Killing of BCG-TNF was associated with rapid accumulation of inducible NO synthase (iNOS) protein and the production of nitrite. The uncontrolled growth of BCG-vector was associated with low iNOS expression but no nitrite production. Thus, iNOS expression appears to be TNF-α independent but iNOS generation of NO requires TNF-α. In cultures of TNF-KO macrophages infected with BCG-TNF, inhibition of iNOS by aminoguanidine (AMG) abolished the killing of the bacilli. However, the growth of the organisms was still inhibited, suggesting an iNOS-independent TNF-α-mediated growth inhibition. To confirm this, macrophages from iNOS-KO mice were infected with either BCG-vector or BCG-TNF. As expected, no nitrite was detected in the culture medium. TNF-α was detected only when the cells were infected with BCG-TNF. In the iNOS-KO macrophages, the growth of BCG was inhibited only in the BCG-TNF infection. These results suggest that in the absence of iNOS activity, TNF-α stimulates macrophages to control the growth of intracellular BCG. Thus, there appears to be both a TNF-α-dependent-iNOS-dependent killing pathway as well as a TNF-α-dependent-iNOS-independent growth inhibitory pathway for the control of intracellular mycobacteria in murine macrophages.

Cutting Edge: Urease Release by Helicobacter pylori Stimulates Macrophage Inducible Nitric Oxide Synthase

“…Most bacteria activate iNOS in macrophages after invasion (21) or by an LPS-mediated pathway (22). Herein, we demonstrate that soluble H. pylori-released proteins cause NO generation by macrophages.…”

Tuberculosis Subunit Vaccination Provides Long-Term Protective Immunity Characterized by Multifunctional CD4 Memory T Cells

“…IFN-␥ is clearly indispensable for resistance to mycobacterial and other intracellular infections (17) and is often used as a single readout for Th1 responses. TNF-␣ is on its own an effector cytokine that can synergize with IFN-␥ to eliminate intracellular pathogens (18,19). It is interesting, therefore, that on a per cell basis the multifunctional cells were 2-4 times more efficient producers of the measured cytokines than the single-positive CD4 T cells.…”

Contribution of Catalase and Superoxide Dismutase to the Intracellular Survival of Clinical Isolates of Staphylococcus aureus in Murine Macrophages

“…TNF-a was found in the lungs of mice experimentally infected with Chlamydia trachomatis and showed that exogenous TNF-a, induced by lipopolysaccharide provided protection from death caused by the pathogen. The presence of TNF-a whether of host or pathogen origin was required [32]. …”