BAFF protein is differentially expressed in lung tissues of female mice with infiltration of foamy macrophages in close proximity to lymphoid follicles; Representative images stained for Ki67 (marker of proliferation) in a) house-dust mite exposed mouse as positive control and b) female smoke-exposed mouse, and CD21 (marker of follicular dendritic cells) in c) mouse spleen as positive control and d) female smoke-exposed mouse are shown. e) Paraffin-embedded lung section showing foamy macrophages (green arrows) located in close proximity to lymphoid follicles is stained with H&E. Scale bar = 50 μm. f) The number of foamy macrophages was normalized to total cross-sectional area (mm2). g) Total number of foamy macrophages per total cross-sectional area was correlated between fractions of follicle area per total cross-sectional area in female mice exposed to air or smoke for 6 months. Representative frozen lung sections from a h) female control and i) smoke-exposed female mouse stained with oil red are shown. Values were expressed as mean ± SEM with N = 5–7 per group. Panel f was analyzed using an one-way ANOVA with Bonferroni’s multiple comparisons test. Linear regression analysis was used in panel g.