Decreased bone marrow progenitors with adipogenic potential and adiposity before RA-like disease onset. No significant difference was found in the number of CFU-F (a) (n = 8) and CFU-O (b) (n = 12) in Balb/c IL-1ra-/- mice when compared to age-matched (age 5 to 12 weeks) wild type mice before disease onset. A significant decrease in CFU-A was found in Balb/c IL-1ra-/- mice (n = 8) but not in C57BL/6 IL-1ra-/- mice (c) (n = 6) when compared to their respective age matched wild type mice. (d) A representative histological section of tibia showing absence of adipocytes in the bone marrow of Balb/c IL1ra-/- and representation of the average percentage of bone marrow area covered by adipocytes in Balb/c IL1ra-/- mice and age matched WT controls (n = 9). Data were analysed by Student t-test. *** P < 0.001. WT, wild type mice; CFU-F, colony forming unit fibroblast; CFU-O, Colony forming unit osteoblast; CFU-A, colony forming unit adipocyte; BM, bone marrow; Ad Ar, adipocyte area; BM Ar, bone marrow area; Oc, osteoclasts; Ob, osteoblasts; BV, bone volume; TV, tissue volume. Black arrows indicate presence of adipocytes.