Pleural tuberculosis in patients with early HIV infection is associated with increased TNF-alpha expression and necrosis in granulomas.

Although granulomas may be an essential host response against persistent antigens, they are also associated with immunopathology. We investigated whether HIV co-infection affects histopathological appearance and cytokine profiles of pleural granulomas in patients with active pleural tuberculosis (TB). Granulomas were investigated in pleural biopsies from HIV positive and negative TB pleuritis patients. Granulomas were characterised as necrotic or non-necrotic, graded histologically and investigated for the mRNA expression of IL-12, IFN-gamma, TNF-alpha and IL-4 by in situ hybridisation. In all TB patients a mixed Th1/Th2 profile was noted. Necrotic granulomas were more evident in HIV positive patients with a clear association between TNF-alpha and necrosis. This study demonstrates immune dysregulation which may include TNF-alpha-mediated immunopathology at the site of disease in HIV infected pleural TB patients.

Associations between toll-like receptors and interleukin-4 in the lungs of patients with tuberculosis.

Toll-like receptors (TLRs) are implicated in the intracellular killing of Mycobacterium tuberculosis, and their expression is modulated by interleukin-4 (IL-4) in vitro. Our aim was to examine the expression of TLRs at the site of pathology in tuberculous lung granulomas and to explore the effect of the immune response on TLR expression. Immunohistochemistry was performed on lung granulomas from nine patients with tuberculosis undergoing lobectomy for haemoptysis. All nine patients expressed all of the TLRs studied (TLRs 1-5 and 9), whereas only five out of the nine patients had any granulomas positive for IL-4. Statistical analysis of TLR and cytokine staining patterns in 183 individual granulomas from the nine patients revealed significant associations between pairs of receptors and IL-4. A positive association between TLR2 and TLR4 (P < 0.0001) and a negative association between TLR2 and IL-4 (P < 0.0001) was observed. The associations between TLRs 1, 5, and 9 were significantly different in IL-4-negative compared with IL-4-positive patients. In conclusion, TLRs are expressed by various cell types in the human tuberculous lung, and their expression patterns are reflected by differences in the immune response.

Localisation of mycobacterial DNA and mRNA in human tuberculous granulomas.

In situ hybridisation was used to detect the presence of Mycobacterium tuberculosis in paraffin-embedded lung tissue of nine patients diagnosed with tuberculosis (TB). Mycobacterial DNA was found in all nine patients and in 175 out of 191 granulomas examined. A combination of in situ hybridisation and immunohistochemistry techniques demonstrated that mycobacterial DNA was associated with CD68-positive cells with the morphology of macrophages and giant cells. Mycobacterial DNA was also found within the necrotic regions of some granulomas. mRNA for the mycobacterial RNA polymerase beta subunit (rpoB) was detected by RNA: RNA in situ hybridisation. The rpoB mRNA was also localised to CD68-positive cells with the morphology of macrophages and to giant cells of certain necrotic granulomas. No rpoB mRNA was found in the necrotic regions of granulomas. Mycobacterial DNA was detected in 92% of patient granulomas of which 8% were positive for rpoB mRNA. The ability to identify mycobacterial RNA transcripts within human tuberculous granulomas affords us the opportunity to analyse the interplay between pathogen gene expression and the human immune response and should provide valuable insight into the mechanisms used by M. tuberculosis to persist within the human host.