HLA-C expression pattern is spatially different between psoriasis and eczema skin lesions.

Interactions between genetic and environmental factors underlie the immune dysregulation and keratinocyte abnormalities that characterize psoriasis. Among known psoriasis susceptibility loci (PSORS), PSORS1 on chromosome 6 has the strongest association to disease. Altered expression of some PSORS1 candidate genes has been reported but little is known about HLA-C expression in psoriasis. This study compared expression of major histocompatibility complex class Ia and HLA-C in psoriasis, allergic contact eczema, and normal skin. Although HLA-C was abundant in protein extracts from both eczema and psoriasis, a consistent and intriguing difference in the expression pattern was observed; strong immunoreactivity in the basal cell layer, polarized towards the basement membrane in psoriasis, whereas in eczema lesions HLA-C immunostaining was present mostly in suprabasal cells. Inflammatory cells in the dermis were strongly stained in both diseases. Normal skin epithelium showed less intense but similar HLA-C staining as eczema lesions. HLA class Ia expression overall resembled that of HLA-C in all samples. The distinct HLA-C expression patterns in psoriasis and eczema suggest a functional role in the specific psoriasis immune response and not only a general feature of inflammation.