Abstract 337: Contribution Of Platelet Par4 To Influenza A Virus Induced Lung Pathology In Mice

Abstract

The influenza A virus (IAV) causes a seasonal respiratory tract infection and is characterized by excessive inflammation and tissue pathology in the lungs. Protease-activated receptor 4 (PAR4) is expressed megakaryocytes/platelets, immune cells, and lung epithelial cells and it is the only functional thrombin receptor on murine platelets. Studies showed that platelets contribute to the pathogenesis of IAV. However, the mechanisms are unknown. While platelet inhibition in IAV infection was protective, a global PAR4 deficiency in mice was associated with increased IAV pathology including mortality. The objective of this study is to investigate the contribution of platelet PAR4 to IAV pathology. Mice (both sex) with PAR4 deficiency on megakaryocytes/platelets (PAR4 fl/fl ;PF4 Cre+ ) and controls (PAR4 fl/fl ) were infected with mouse adapted IAV (H1N1/PR8) at a dose, which induces 20% mortality in control mice. Inflammatory mediators and cellular inflammation in bronchoalveolar lavage fluid (BALF) was analyzed before, 3, 5 and 7 days post infection (dpi). Body weight changes were analyzed over 14 dpi and survival calculated with a human endpoint of a body weight loss of ≥25% initial weight. Lastly, lung function was analyzed by noninvasive whole-body plethysmography at 0 and 7 dpi. There were no significant differences in the analyzed inflammatory mediators, except for IFNγ, IL6, and protein, or any immune cell numbers in the BALF of both genotypes at any time point after infection. Both genotypes exhibited similar body weight changes over the course of infection which resulted that mice of both genotypes exhibited a mortality of approx. 20%. However, the lung function parameters calculated as PenH (airway resistance) and EF50 (flow rate at 50% expired volume) were significant higher in PAR4 fl/fl ;PF4 Cre+ compared to PAR4 fl/fl mice 7 dpi. Platelet PAR4 does not influence pathology in a mild IAV infection model. However, the more severe pulmonary dysfunction in PAR4 fl/fl ;PF4 Cre+ compared to PAR4 fl/fl mice suggest a protective role of platelet PAR4 in maintaining lung function during IAV infection. More studies are needed to investigate if the contribution of platelet PAR4 to IAV pathology is dependent on disease severity as recently suggested.