Regional cytokine responses to pulmonary aspergillosis in immunocompetent rats

Abstract

Rat models of pulmonary aspergillosis are used widely in diagnostic studies and in exploring antifungal therapeutic modalities, but there is lack of data concerning antifungal immunity in rats. In this study, cytokine response to pulmonary infection to Aspergillus fumigatus in non-immunosuppressed rats is explored. Temporal display (from the start of infection up to its eradication) of proinflammatory cytokines (IFN-γ and IL-17) as well as Th2/anti-inflammatory ones (IL-4 and IL-10) was explored by measuring their presence in the environment in which elimination of infection occur (lung homogenates), by production of these mediators by lung cells (recovered by enzyme digestion or by bronchoalveolar lavage) as well as by cells of draining lymph nodes (as sites of generation of cytokine-producing cells). Reduction of infection (1 × 10⁷conidia) was associated with an increase of IFN-γ and IL-17 content in lung homogenates, but with unchanged IL-4 and IL-10 content. Lung cells produced proinflammatory cytokines with differential dynamics (IFN-γ earlier than IL-17). Differential pattern of Th2/anti-inflammatory cytokine production by lung cells was observed (unchanged IL-4 and increased IL-10), with the levels of the latter higher than proinflammatory cytokines. Upregulation of IFN-γ, IL-17 and IL-10 production and gene expression, but downregulation of IL-4, by draining lymph node cells (dLN cells) accounted essentially for the observed ex vivo cytokine response in lungs. Similar pattern of cytokine production by dLN cells following restimulation with A. fumigatus conidia confirmed the specificity of cytokine response to the fungus. Draining lymph node CD4⁺ cells seems to be the main source of proinflammatory cytokines, significant contributors to IL-10 production and the target for down regulation of IL-4. The knowledge of immune-based mechanisms of defense against A. fumigatus in rats might be helpful in the future use of rat models of pulmonary aspergillosis particularly those that develop immune-based therapeutic interventions as an adjunct treatment of fungal diseases.

Keywords: A. fumigatus; Aspergillus fumigatus; BAL; CFU; ELISA; H&E; IFN-γ; IL; IL-10; IL-17; IL-4; MPO; NBT; NK cells; Pulmonary infection; RT-PCR; Rats; SMA; Sabouraud's maltose agar; T helper; TLR; Th; Toll-like receptor; bronchoalveolar lavage; cDNA; colony forming units; complementary DNA; dLN; draining lymph node; enzyme-linked immunosorbent assay; hematoxylin and eosin; interferon-γ; interleukin; mRNA; messenger RNA; myeloperoxidase; natural killer cells; nitroblue tetrazolium; p.i.; post infection; real-time polymerase chain reaction.