Histology of the carpal joint in TTP/TNFR-deficient mice.

(A-C) Hematoxylin-eosin–stained sections of the carpal joint of 6-month-old mice at × 10 magnification, with the metacarpal bones to the left and the radius and ulna to the right; the radial head is on top in each section. (A) Carpal joint of a mouse deficient in TTP and both TNFRs. (B) Carpal joint from a mouse deficient in TTP and TNFR1. (C) Carpal joint from a mouse deficient in TTP and TNFR2. Both (A) and (B) demonstrate a clean articular cavity, smooth articular surfaces, and absence of inflammation or pannus formation. In contrast, (C) demonstrates the presence of severe inflammation, with erosion of the articular surfaces and invasion of the articular cavity by the prominent pannus. All 3 genotypes (A-C) exhibit marked intramedullary hypercellularity. (D) Higher-power view (× 100 magnification) of the area delimited by the box in (C). The cellular component of the inflammatory infiltrate is of both polymorphonuclear (arrowhead) and mononuclear (arrow) lineages.