Altered Expression of Surfactant and CD74 in the Alveolar Epithelial Cells During Influenza Infection Disease

Abstract Background Influenza A virus (IAV) causes substantial morbidity and mortality in the human population. In the lower lung, the primary targets for IAV replication are type II alveolar epithelial cells (AECII), which are increasingly recognized for their immunological potential. Surfactant components are synthesized primarily by AECII, which play an important role in host defense against infection. On the other side, AECII express high levels of CD74 and contributes to repair the damaged alveolus during infection. Aim To analyze the expression of surfactant (proSP-C), CD74 and activation markets (HLA-DR, CD80, CD86) expressed by AECII cells from infected mice and A549 cell line. Methods IAV used include the mouse adapted influenza strains. Pandemic H1N1 (pH1N1) and A/Victoria/3/75 (H3N2) were used to infect BALB/c mice. AECII cells were obtained from mice lungs, and cell suspensions obtained from enzymatically digested murine lungs were labeled for surface antigens (CD45/CD31/CD74/proSP-C) followed by FACS analysis. The A549 cell line was used as a human in vitro model and to compare the results. Results Analysis of AECII phenotype showed a significant decrease of proSP-C+CD31−CD45−and CD74+CD31−CD45− expression in infected mice comparing to controls, and also in the group infected with H1N1 vs H3N2 (MFI p <0.01; p<0.05, respectively). Expression of HLA-DR was very low for AECII and A549 cell line in infection condition. However, CD80 and CD86 they did not show changes in their expression. Conclusions Our results indicate that morphological changes in AECII phenotype suggest very active participation of alveolar epithelial cells in inflammatory viral processes in the lung, and higher effects of H1N1 comparing to H3N2 strain.