Host lung immunity is severely compromised during tropical pulmonary eosinophilia: role of lung eosinophils and macrophages

Abstract

Eosinophils play a central role in the pathogenesis of tropical pulmonary eosinophilia, a rare, but fatal, manifestation of filariasis. However, no exhaustive study has been done to identify the genes and proteins of eosinophils involved in the pathogenesis of tropical pulmonary eosinophilia. In the present study, we established a mouse model of tropical pulmonary eosinophilia that mimicked filarial manifestations of human tropical pulmonary eosinophilia pathogenesis and used flow cytometry-assisted cell sorting and real-time RT-PCR to study the gene expression profile of flow-sorted, lung eosinophils and lung macrophages during tropical pulmonary eosinophilia pathogenesis. Our results show that tropical pulmonary eosinophilia mice exhibited increased levels of IL-4, IL-5, CCL5, and CCL11 in the bronchoalveolar lavage fluid and lung parenchyma along with elevated titers of IgE and IgG subtypes in the serum. Alveolar macrophages from tropical pulmonary eosinophilia mice displayed decreased phagocytosis, attenuated nitric oxide production, and reduced T-cell proliferation capacity, and FACS-sorted lung eosinophils from tropical pulmonary eosinophilia mice upregulated transcript levels of ficolin A and anti-apoptotic gene Bcl2,but proapoptotic genes Bim and Bax were downregulated. Similarly, flow-sorted lung macrophages upregulated transcript levels of TLR-2, TLR-6, arginase-1, Ym-1, and FIZZ-1 but downregulated nitric oxide synthase-2 levels, signifying their alternative activation. Taken together, we show that the pathogenesis of tropical pulmonary eosinophilia is marked by functional impairment of alveolar macrophages, alternative activation of lung macrophages, and upregulation of anti-apoptotic genes by eosinophils. These events combine together to cause severe lung inflammation and compromised lung immunity. Therapeutic interventions that can boost host immune response in the lungs might thus provide relief to patients with tropical pulmonary eosinophilia.

Functional Impairment of Murine Dendritic Cell Subsets following Infection with Infective Larval Stage 3 of Brugia malayi

“…However, the effects of filarial worms on various subsets of host DCs during the very early stages of infection remain obscure. Recently, using a mouse model of TPE, we showed that the pathogenesis of TPE is characterized by functional impairment of alveolar macrophages (AMs), alternative activation of lung macrophages, and upregulation of antiapoptotic genes by eosinophils, which led to severe lung inflammation and compromised host lung immunity (11). Extrapolating our findings even further, in the present study, we infected BALB/c mice with infective Bm-L3 and studied the effect of this infection on flow-sorted DC subsets present in the secondary lymphoid organs of mice.…”

“…Briefly, single-cell suspensions of spleens from at least 6 to 8 identically treated mice were pooled, and CD11c-positive cells were enriched using CD11c beads, as described above. Sorting was carried out using a high-speed FACS Aria flow cytometer (BD Biosciences) fitted with a 70-m nozzle, as described recently (11,67). After sorting, the sorted cells were subjected to analysis to ascertain their purity, and a small fraction was used to prepare cytospins (Fig.…”

“…Next, they were fixed, permeabilized, and distributed equally into four separate tubes, followed by addition of PE-labeled anti-mouse monoclonal antibodies directed against TNF-␣, IL-12, IL-4, and IL-10. Data acquisition and compensation were done on a FACS Aria flow cytometer, and analysis was done using FACS DIVA software, as described recently (11).…”

“…The T-cell proliferation capacities of FACS-sorted mDCs, LDCs, and pDCs were estimated by coculturing each DC subset (n ϭ 5,000) with 2 ϫ 10 5 CD4 ϩ T cells that were purified from the spleens of naive mice using CD4 magnetic beads (Miltenyi Biotec). The cells were cocultured in 96-well flat-bottom plates (Corning) for 48 h in a CO 2 incubator at 37°C, and mitochondrial activity, as a measure of T-cell proliferation, was subsequently measured by XTT assay as described recently (11).…”

“…Impairment of host Langerhans cells has also been reported during lymphatic filarial infections, which suggests that parasites not only interfere with the functions of Langerhans cells, but have also developed means to expertly evade antigen (Ag)-presenting cell (APC) detection in the host skin (1,10). We recently documented the role of lung eosinophils and functional impairment of lung macrophages during filarial manifestation of tropical pulmonary eosinophilia (TPE) (11). This is important, as macrophages, along with DCs, not only are a heterogeneous group of APCs, but immature DCs circulate in the peripheral blood, where they capture, process, and present antigens (12).…”