PD-L1 and PD-L2 affect the sensitivity and the degree of lung inflammation after infection with IAV.

<p>PD-L2^−/−, PD-L1^−/− and BALB/c (n = 10) mice received a lethal dose of IAV (3000 PFU) intranasally. (<b>A</b>) Weight loss has been monitored by measuring body weight daily post infection (DPI) (<b>B</b>) BAL was performed in mice (n = 5) five days post IAV infection and analyzed for differential cellular infiltration. Bar graph shows total cell number (Total) and absolute number of eosinophils (EOS), monocytes/macrophages (MAC), lymphocytes (LYM) and neutrophils (PMN). ND: not detectable. (<b>C</b>) Representative image of lung sections taken 5 days post infection with 3000 PFU IAV stained with H&E (original magnification ×40, insert magnification ×100, scale bar 50 μm) from BALB/c, PD-L1^−/− and PD-L2^−/− mice. (<b>D</b>) Quantification of lung sections as shown by measurement of thickness of epithelium, left panel and number of inflammatory cells per 250 µm², right panel. (<b>E</b>) Virus titration in the lungs shown as plaque forming units (PFU) per gram of lung tissue. Data are presented as mean ± SEM, * P>0.05, ** P>0.01 and *** P>0.001 as calculated by a one-way ANOVA with Tukey post hoc test and is representative of four independent experiments.