Fig. 1: Type II alveolar cells (AT2s) constitutively express MHCII independent of conventional inflammatory signals.

a–c MHCII protein expression by AT2s from naive C57Bl/6 (B6) wild-type (WT) and MHCII^−/− mice (a) and AT2s, CD103⁺ dendritic cells (CD103⁺ DC), B cells, alveolar macrophages (Alv mac), and endothelial cells (EC), from naive B6 WT lungs (b, c) measured by flow cytometry; histograms represent n > 10 mice per strain total from >5 experiments. WT AT2s are in blue (a–c), MHCII^−/− AT2s in black (a), and other WT cell types in gray as labeled (b, c). d I-A^b α (H2-Aα) and β (H2-Aβ1) chain transcript abundance relative to housekeeping gene Hprt1, in AT2s and lung dendritic cells (DC) sorted from naive B6 WT mice, and a B6 fibroblast cell line (B6 Fib), measured by quantitative RT-PCR; symbols are biological replicates, n = 3 mice for AT2s, n = 2 for DCs, n = 1 for the cell line, each calculated as the average of three technical replicates; one representative experiment shown of two similar experiments. e MHCII protein expression by AT2s in MHCII^−/− and CD45.1 B6 (B6^CD45.1) bone marrow chimeras, measured 8 weeks post-transplantation, with different transfers shown in shades of blue as labeled; histograms represent n = 2 [B6^CD45.1 → MHCII^−/−], n = 3 [B6^CD45.1 → B6^CD45.1], n = 3 [MHCII^−/− → MHCII^−/−], n = 4 [MHCII^−/− → B6^CD45.1] mice. f, g MHCII protein expression by AT2s, CD103⁺ DCs, ECs from naive B6 WT, MHCII^−/− (f, g) Ciita^−/−, Ciita pIV^−/− (f), Ifng^−/−, Ifngr1^−/−, and Stat1^−/− (g) lungs, measured by flow cytometry. Each symbol reflects MHCII expression on the cell type indicated in n = 1 mouse, with n = 5 per strain total pooled from 2 experiments for all strains, except Ifngr1^−/−, which was pooled from three experiments. MHCII expression is quantified as a percentage reflecting the average median fluorescence intensity (MFI) of MHCII on each cell type in a given knockout mouse relative to the MHCII MFI on the same cell type in WT mice. 3/5 Ciita pIV^−/− were 8 months old, 1/5 Ifngr1^−/− were 5 months old. WT mice are in black, other knockout strains in shades of gray as labeled. d, f, g Bars are mean plus standard error of the mean (SEM). Source data are provided as a Source data file.