The role of alveolar type II cells in swine leptospirosis

摘要

: This study aimed to investigate a possible relationship between alveolar type II cells and the inflammatory response to infection with Leptospira spp., and thus comprise a further element that can be involved in the pathogenesis of lung injury in naturally infected pigs. The study group consisted of 73 adult pigs that were extensively reared and slaughtered in Teresina, Piau?- state, and Timon, Maranh?￡o state, Brazil. The diagnosis of leptospirosis was made using the microscopic agglutination test (MAT) aided by immunohistochemistry and polymerase chain reaction. The MAT registered the occurrence of anti-Leptospira antibodies in 10.96% (8/73) of the pigs. Immunohistochemistry allowed for the visualization of the Leptospira spp. antigen in the lungs of 87.67% (64/73) of the pigs. There was hyperplasia of bronchus-associated lymphoid tissue and circulatory changes, such as congestion of alveolar septa, parenchymal hemorrhage and edema within the alveoli. Lung inflammation was more intense (p = 0.0312) in infected animals, which also showed increased thickening of the alveolar septa (p = 0.0006). Evaluation of alveolar type II (ATII) cells using an anti-TTF-1 (Thyroid Transcription Factor-1) antibody showed that there were more immunostained cells in the non-infected pigs (53.8%) than in the infected animals (46.2%) and that there was an inverse correlation between TTF-1 positive cells and the inflammatory infiltrate. There was no amplification of Leptospira DNA in the lung samples, but leptospiral DNA amplification was observed in the kidneys. The results of this study showed that a relationship exists between a decrease in alveolar type II cells and a leptospire infection. Thus, this work points to the importance of studying the ATII cells as a potential marker of the level of lung innate immune response during leptospirosis in pigs. Index Terms??Alveolar type II cells; immunohistochemistry; Leptospira spp.; lung; swine. Resumo Setenta e tr?as su?-nos adultos de cria?§?￡o extensiva, abatidos em Teresina, no estado do Piau?- e Timon, no estado do Maranh?￡o, constitu?-ram o grupo de estudo. O diagn?3stico da leptospirose foi realizado utilizando a t??cnica de soroaglutina?§?￡o microsc?3pica (MAT), auxiliada por imunoistoqu?-mica e rea?§?￡o em cadeia pela polimerase. A SAM registrou a ocorr?ancia de anticorpos anti-leptospiras em 10,96% (8/73) dos su?-nos. A imunoistoqu?-mica permitiu a visualiza?§?￡o de ant?-genos de Leptospira spp. em pulm?μes de 87,67% (64/73) dos su?-nos. Havia hiperplasia do tecido linfoide associado ao br?′nquio e altera?§?μes circulat?3rias como, congest?￡o do septo alveolar, hemorragia parenquimatosa e edema no interior de alv??olos. Os focos de inflama?§?μes pulmonares eram mais numerosos (p=0,0312) nos animais infectados, bem como o espessamento do septo alveolar (p=0,0006). A quantifica?§?￡o de c??lulas alveolares tipo II marcadas pelo anticorpo anti-TTF-1 (Thyroid Transcription Factor-1) mostrou que existia mais c??lulas imunocoradas em su?-nos n?￡o infectados (53,8%) comparados aos infectados (46,2%) e uma correla?§?￡o inversa em rela?§?￡o ao infiltrado inflamat?3rio. N?￡o houve amplifica?§?￡o de DNA de Leptospira spp. em amostras de tecido pulmonar, no entanto DNA leptospiral foi observado em rim. Os resultados deste estudo mostraram que existe uma rela?§?￡o entre a diminui?§?￡o das c??lulas alveolares tipo II e a infec?§?￡o por leptospiras. Dessa forma, este trabalho aponta para a import?￠ncia do estudo dessas c??lulas, como um prov??vel marcador da modula?§?￡o da resposta imune inata do pulm?￡o na leptospirose em su?-nos. Termos de Indexa?§?￡o??C??lulas alveolares tipo II; imunoistoqu?-mica; Leptospira spp.; pulm?￡o; su?-no. Introduction The alveoli of mammals are composed of endothelial cells with metabolic functions that participate in gas exchange, alveolar macrophages that coordinate the body's defenses, interstitial fibroblasts that secrete extracellular matrix components to support the honeycomb structure of the matrix, alveolar type I cells that mediate gas exchange, and alveolar type II cells (ATII) that have secretory functions, proliferate and mediate innate immunity (Herzog 2008). ATII cells are important sources of pulmonary surfactants (SP-A, SP-B, SP-C and SP-D). These lipoproteins prevent alveolar collapse (Halliday 2008), mediate innate immunity (Chroneos et al. 2010), regulate the function of inflammatory cells through the secretion of a variety of cytokines and chemokines (Faine 1999), secrete growth factors, such as vascular endothelial growth factor (VEGF) (Zissel et al. 2000,Ferrara et al. 2003), complement components (Singh et al. 1988) and adhesion molecules, and present antigens in the context of MHC class II (Cunningham et al. 1994) molecules, thus providing ATT cells with properties similar to those of antigen-presenting cells (Debbabi et al. 2005). ATII cells account for 15% of total alveolar cells but only constitute 5% of the alveolar surface in