Figure 1.

4-1BB deficiency in MRL-Fas^lpr (lpr) mice causes acute skin lesions, lymphadenopathy, and early mortality. (a) Representative photographic images of 5-month-old lpr/4-1BB^+/+ (+/+) and lpr/4-1BB^–/– (–/–) mice. *The lpr/4-1BB^+/+ (+/+) mice were treated subcutaneously from age 1 month with agonistic anti-4-1BB monoclonal antibody (100 µg twice weekly) and visible skin lesions were assessed at age 5 months. Note the acute skin lesions and ear pinna loss in lpr/4-1BB^–/– mice (arrows and dashed circles). (b) Skin lesions in (a) were graded as mentioned in the Materials and methods. (c, d) Size distribution (c) and tissue weights (d) of spleens and lymph nodes in 5-month-old mice. *P < 0·001.