Cytokine and Eosinophil Responses in the Lung, Peripheral Blood, and Bone Marrow Compartments in a Murine Model of Allergen-induced Airways Inflammation

Selective accumulation of eosinophils and activated CD4⁺ cells is now considered a central event in the pathogenesis of asthma, and this process is thought to be mediated by a number of cytokines including tumor necrosis factor-α (TNF-α), granulocyte-macrophage colony-stimulating factor (GM-CSF), and the Type 2 cytokines interleukin-4 (IL-4) and IL-5. To carry out a detailed time-course analysis of cellular changes in the bronchoalveolar lavage fluid (BAL), peripheral blood (PB), and bone marrow (BM), and of changes in the aforementioned cytokines in BAL and serum, Balb/c mice were sensitized by intraperitoneal injection with ovalbumin (OVA) adsorbed to aluminum hydroxide on two occasions 5 days apart, and were subjected to an OVA aerosol challenge 12 days after the second sensitization. This resulted in an airways inflammatory response characterized by early transient neutrophilia, marked eosinophilia, and, to a lesser extent, lymphocytosis in the BAL. Inflammatory events were first observed 3 h and 24 h after antigen challenge in the lung tissue and BAL, respectively, and lasted for 21 days. In the BM, we detected a 1.5- and 5-fold increase in the total number of cells and eosinophils, respectively, 4 days after the second sensitization. This was followed by a decrease, although BM eosinophilia remained clearly present at the time of antigen challenge. A second eosinopoietic event was observed in the BM shortly after challenge and reached a peak at day 3. BM cellularity returned to normal at day 21 after challenge. Serum OVA-specific IgE was first detected 3 days following the second sensitization (150 ng/ml). IgE levels then decreased but remained at the 75 ng/ml range at the time of the aerosol challenge. During the sensitization period, TNF-α (≈ 25 pg/ml), IL-4 (≈ 40 pg/ml), and IL-5 (≈ 250 pg/ml) were detected in serum, but not in the BAL fluid (BALF) and returned to background levels at the time of the antigen challenge. After antigen challenge, TNF-α, IL-4, IL-5, and GM-CSF were detected in serum. Peak levels were observed at 3 h (≈ 40 pg/ml), 3 h (≈ 120 pg/ml), 12 h (≈ 350 pg/ml), and 3 h (≈ 10 pg/ml), respectively, and returned to background levels 24 h after challenge. In the BALF, we detected peak levels of TNF-α, IL-4, IL-5, and GM-CSF at 6 h (≈ 250 pg/ml), 24 h (≈ 140 pg/ml), 24 h (350 pg/ml), and 3 h (≈ 10 pg/ml), respectively, with a return to background levels 5 days after challenge. No IL-10 could be detected at any time point during sensitization or after challenge in either serum or BAL. We also detected approximately 40 pg/ml of interferon-γ (IFN-γ) in the serum of normal untreated mice. Serum IFN-γ levels fluctuated during sensitization and after challenge, but never exceeded those observed in untreated mice. Thus, the cytokine profile observed in this experimental model of allergic inflammation is characterized by IL-4 and IL-5 dominance, with an apparently minor TNF-α and GM-CSF contribution and relatively low or undetectable levels of IFN-γ and IL-10.