Relative importance of NF-kappaB p50 in mycobacterial infection

Abstract

To understand the role of NF-kappaB in the development of murine tuberculosis in vivo, NF-kappaB p50 knockout mice were infected with Mycobacterium tuberculosis by placing them in the exposure chamber of an airborne-infection apparatus. These mice developed multifocal necrotic pulmonary lesions or lobar pneumonia. Compared with the levels in wild-type mice, pulmonary inducible nitric oxide synthase, interleukin-2 (IL-2), gamma interferon, and tumor necrosis factor alpha mRNA levels were significantly low but expression of IL-10 and transforming growth factor beta mRNAs were within the normal ranges. The pulmonary IL-6 mRNA expression level was higher. Therefore, NF-kappaB and its interaction with host cells play an important role in the pathogenesis of tuberculosis.

FIG. 1

Survival curves of mice infected with M. tuberculosis Kurono strain. The data presented are from two separate experiments with 10 mice in each group.

FIG. 2

CFU in lung and spleen tissues of NF-κB KO and WT mice (10 mice each) exposed to 10⁶ CFU of M. tuberculosis Kurono strain by the airborne route. At the indicated days after infection, three mice from each group were sacrificed and homogenates of lung and spleen tissues were plated. Error bars indicate standard deviations of the means.

FIG. 3

Histologic examination of lung tissues. Mice were killed 5 weeks after airborne infection with M. tuberculosis Kurono strain, and formalin-fixed sections were stained with hematoxylin and eosin (A and C) or Ziehl-Neelsen stain for acid-fast bacilli (B). (A) Pulmonary tissue from an NF-κB KO mouse infected with Kurono strain. Almost necrotic lesions with numerous neutrophils and epithelioid macrophages (arrow) are shown. Magnification, ×315. (B) Pulmonary tissue from an NF-κB KO mouse infected with Kurono strain. Many acid-fast bacilli are recognized in the necrotic lesion by Ziehl-Neelsen staining. Magnification,×540. (C) Pulmonary tissue from a WT mouse infected with Kurono strain. A discrete granulomatous lesion is recognized. Magnification, ×135.

FIG. 4

Electron micrographs of lung tissue from WT (a) and NF-κB KO (b) mice infected with Kurono strain, obtained 5 weeks after airborne infection. (a) Phagolysosomal fusion (arrows) incorporating many tubercle bacilli is prominent. Magnification, ×5,000. (b) Many phagosomes (arrows) ingest tubercle bacilli. Magnification, ×5,000.

FIG. 5

In vivo expression of various cytokines and iNOS mRNA in Kurono strain-infected mice by RT-PCR. The lung tissues of NF-κB KO and WT mice were removed 1, 3, 5, and 7 weeks after airborne infection. β-Actin gene primer sets were used as an internal control. IFN-γ, IL-2, IL-1β, IL-12, iNOS, and TNF-α mRNA expression is low in NF-κB KO mice. W, wild type; K, knockout; M, size marker.