Objective To evaluate immunologic mechanisms underlying Aspergillus fumigatus pulmonary infections in immunocompetent Dark Agouti(DA) and Albino Oxford(AO) rats recognized as being susceptible to some inflammatory diseases in different manners. Methods Lung fungal burden(quantitative colony forming units, CFU, assay), leukocyte infiltration(histology, cell composition) and their function(phagocytosis, oxidative activity, CD11 b adhesion molecule expression) and cytokine interferon-γ(IFN-γ) and interleukin-17 and-4(IL-17 and IL-4) lung content were evaluated following infection(intratracheally, 1x107 conidia). Results Slower reduction of fungal burden was observed in AO rats in comparison with that in DA rats, which was coincided with less intense histologically evident lung cell infiltration and leukocyte recovery as well as lower level of most of the their activities including intracellular myeloperoxidase activity, the capacity of nitroblue tetrazolium salt reduction and CD11 b adhesion molecule expression(except for phagocytosis of conidia) in these rats. Differential patterns of changes in proinflammatory cytokine levels(unchanged levels of IFN-γ and transient increase of IL-17 in AO rats vs continuous increase of both cytokines in DA rats) and unchanged levels of IL-4 were observed. Conclusion Genetically-based differences in the pattern of antifungal lung leukocyte activities and cytokine milieu, associated with differential efficiency of fungal elimination might be useful in the future use of rat models in studies of pulmonary aspergillosis. Objective To evaluate the immunological mechanisms underlying Aspergillus fumigatus pulmonary infections in immunocompetent Dark Agouti (DA) and Albino Oxford (AO) rats recognized as being susceptible to some inflammatory diseases in different manners. Methods Lung fungal burden (quantitative colony forming units, CFU, assay) , leukocyte infiltration (histology, cell composition) and their function (phagocytosis, oxidative activity, CD11 b adhesion molecule expression) and cytokine interferon- γ (IFN- γ) and interleukin- 17 and-4 lung content was evaluated following infection (intratracheally, 1x107 conidia). Results Slower reduction of fungal burden was observed in AO rats in comparison with that in DA rats, which was coincident with less intense histologically induced lung cell infiltration and leukocyte recovery as well as lower level of most of the activities including intracellular myeloperoxidase activity, the capacity of nitroblue tetrazolium salt reduction and CD11 b adh Differential patterns of changes in proinflammatory cytokine levels (unchanged levels of IFN-γ and transient increase of IL-17 in AO rats vs continuous increase of both cytokines in DA rats) and Conclusion Conclusion Genetically-based differences in the pattern of antifungal lung leukocyte activities and cytokine milieu, associated with differential efficiency of fungal elimination might be useful in the future use of rat models in studies of pulmonary aspergillosis.