The phenotypic profile of dermatomyositis and lupus erythematosus: a comparative analysis

The mechanisms which regulate cutaneous inflammation in the setting of collagen vascular disease have been a topic of recent interest; emphasis has been placed on type I interferon-associated recruitment of CXCR3+ lymphocytes in dermatomyositis (DM).

On a total of 42 biopsies from patients with DM, systemic lupus erythematosus (SLE), discoid lupus erythematosus (DLE) and subacute cutaneous lupus erythematosus (SCLE) comprehensive phenotypic studies were performed to explore the practical value of phenotypic analysis in the subclassification of lesions of collagen vascular disease.

The infiltrate in DM was of mild intensity compared to lupus erythematosus (LE). The dominant mononuclear cell in DM exhibited a CD4/CXCR3-positive phenotype while biopsies of SLE typically showed a dearth of CXCR3-positive cells. CD8 and CD20 lymphocytes were greatest in SLE and DLE, respectively. CD123 plasmacytoid dendritic cells, seen in most cases, were most frequent in cases of SCLE; CD83 expression was minimal. Endothelial MXA expression was a characteristic feature of DM. CD123 and MXA expression within inflammatory cells and keratinocytes was most conspicuous in areas of interface injury. Cutaneous lymphocyte antigen (CLA) expression was diminished in the dermal infiltrate in most cases of DM and LE. T regulatory cells never exceeded 15% of the infiltrate and were the least in the setting of DM and LE.

An interferon-alpha-inducible cytokine milieu is common in SLE, DLE, SCLE and DM. In addition, there are phenotypic differences as alluded to above that may be of some practical value in separating these distinctive subsets. Features not previously emphasized such as MXA endothelial cell staining in DM and the lack of staining for CD83 and CLA in lesions of collagen vascular disease may be of diagnostic value.