Major histocompatibility complex (MHC) class I chain-related gene A and B (
MICA and MICB) are located very close to
HLA-B.
MICA is reported to be strongly associated with Behçet's disease (BD), a multisysytemic
inflammation disorder characterized by oral apthous
ulcers, skin lesions and genital
ulcers. These two molecules are highly conserved at the
amino acid levels. To determine the function of MICB in vivo and the relationship between the expression of MICB and BD experimentally, we produced several transgenic mouse lines (termed CAG-MICB) expressing human MICB
cDNA under a ubiquitous promoter. They exhibited a 50% increase in the number of white blood cells compared with their non-transgenic littermates, and also exhibited
a 10-20% reduction in
body weight compared with non-transgenic littermates. Exfoliation of the skin first appeared around 7 days after birth and disappeared after 2 weeks of age. This was repeatedly observed in the transgenic offspring of two independent CAG-MICB lines examined. Histopathological analysis of skin of young mice exhibiting
skin abnormalities revealed hyperkeratosis of the epidermis and thickening of the granular layer with slight infiltration of inflammatory cells in the dermis without any
vasculitis. Other remarkable abnormalities associated with BD have not been observed in the CAG-MICB lines. Furthermore,
fluorescein angiography of eyes of the CAG-MICB lines was performed, but there were no marked changes of BD-related
uveitis in the ocular fundus. These findings suggest that (i) MICB expression is related to temporary skin
inflammation, and (ii) expression of MICB is not directly associated with BD.