Inflammatory responses in mice after intratracheal instillation of microbes isolated from moldy buildings

Abstract

Moisture-damage is common in buildings, and it is associated with a variety of adverse health effects, especially inflammatory responses in the lower airways.Exposure to microbial spores or cells has been suspected to be one reason for the inflammation, but the inflammatory and toxic potential of the microbes has not been well characterized.In this study, a mouse model was devised to elucidate and compare the adverse effects provoked by microbes isolated from the indoor air of a moisture-damaged building.The animals were exposed intratracheally to the microbial spores or cells.The effects caused by the bacterial species Streptomyces californicus and Mycobacterium terrae and the fungi Aspergillus versicolor and Penicillium spinulosum were investigated.They are typical microbes observed in moisture-damaged buildings, but P. spinulosum is also frequently observed in all indoor air environments.Both the dose-response and time-course of the inflammatory and toxic responses were investigated after a single dose of the microbe.Biochemical parameters indicating inflammation and/or toxicity (tumor necrosis factor , TNF, interleukin-6, IL-6, total protein, albumin, hemoglobin and lactate dehydrogenase) were measured from bronchoalveolar lavage fluid (BALF), and a histopathological analysis was performed from lungs, lymph nodes and spleen.In addition, inducible nitric oxide synthase (iNOS) was determined from lavaged cells, and the cytokine concentrations were measured in serum.Moreover, the effects of S. californicus were studied after repeated dosing of the spores.In that experiment also lymphocyte subpopulations were investigated in the lungs, lymph nodes and the spleen.Both the biochemical parameters and histopathology revealed that all the microbes studied provoked inflammation after a single dose, but the magnitude and its characteristic features were different.The spores of S. californicus provoked a very intense acute inflammation indicated by a strong and rapid IL-6 and TNF production in the lungs, recruitment of inflammatory cells into the airways, and expression of inducible nitric oxide synthase (iNOS) in lavaged cells at 24 hours.An increase in TNF and IL-6 concentrations in serum was also detected.The cells of M. terrae induced a biphasic inflammatory response, which consisted of an acute and a sustained phase.In the acute phase, TNF and IL-6 were produced and inflammatory cells were recruited into the lungs.In the later phase, TNF production was sustained up to 14 days, and inflammatory cell recruitment was even more intense, with iNOS being expressed in lavaged cells.Reactive changes in lymph nodes were also observed.The inflammatory response lasted until the end of the experiment (28 days), and at that time some mycobacterial cells were still present in the lungs.At comparable volumetric doses with the bacteria, the fungal species also induced a rapid production of proinflammatory cytokines, and inflammatory cell recruitment into the airways, but they were generally less potent than the bacteria.P. spinulosum induced only a mild inflammatory response and transient TNF and IL-6 production into BALF.The spores of A. versicolor caused a slow TNF response, and the inflammatory cell response was more sustained than by P. spinulosum.In contrast to the bacteria, the studied fungal species did not induce expression of iNOS.Acute cytotoxicity in lungs indicated by LDH response was observed during S. californicus, M. terrae and A. versicolor exposure.M. terrae exposure caused the strongest and most sustained effect.However, none of the microbes were highly cytotoxic in the lungs, and the effect was frequently associated with an acute inflammatory response.P. spinulosum exposure showed no cytotoxic effect.