Microdissection of the cytokine milieu of pulmonary granulomas from tuberculous guinea pigs

Levels of IL-12p40, TNFα, TGFβ, IFNγ and IL-10 mRNA were assessed by laser capture microdissection followed by quantitative real-time PCR in the pulmonary granulomas of unimmunized and BCG-vaccinated guinea pigs infected by aerosol with virulent Mycobacterium tuberculosis. Lesions microdissected from unimmunized guinea pigs were overwhelmed by the pro-inflammatory TNFα mRNA at both 3 and 6 weeks post infection, indicating the struggle to control the mounting infection. The cytokine profile of granulomas from vaccinated guinea pigs shifted from type 1 cytokine mRNA (IFNγ and IL-12p40) at 3 weeks to a predominantly anti-inflammatory environment (TGFβ mRNA) at 6 weeks. The relative proportions of cytokine mRNA transcripts in the periphery of the granuloma were different from the centre, reflecting differences in cell composition and architecture. Moreover, analysis of the individual lung lobes at 6 weeks post infection suggests that heterogeneity exists in the cytokine profile between the lobes of the lung.