Immunologic aspects of scleroderma.

Recent investigations of immunologic events in systemic sclerosis focus on the identification of which immune system cells are participating in the disease process, what antigens are stimulating the T and B cells, which cytokines are involved, and which cell adhesion molecules promote cell-cell and cell-extracellular matrix interactions. Increased numbers of gamma/delta and activated CD4+ T cells are present in involved skin of line-200 chickens, an animal model of systemic sclerosis. CD4+ T cells from patients with systemic sclerosis are stimulated by human type I collagen, and immunoglobulins from some patients with systemic sclerosis bind retroviral proteins, the terminal galactosyl (alpha 1-3)-galactose disaccharide of laminin, or a 138 amino acid region of the PM-Scl antigen. The development of an anticentromere antibody response in patients with systemic sclerosis appears to require the presence of a polar amino acid at position 26 in the antigen-binding cleft of the HLA-DQB1 molecule. Interleukin-2, interleukin-4, interleukin-6, and transforming growth factor-beta have been implicated as cytokines that may be involved in the pathogenesis of systemic sclerosis. Increased expression of intercellular adhesion molecule 1 (ICAM-1) on systemic sclerosis fibroblasts is responsible for increased binding of T cells to those fibroblasts through ICAM-1/lymphocyte function-associated antigen 1 interactions. beta 1 and beta 2 integrins, ICAM-1, and endothelial leukocyte adhesion molecule 1 all may be involved in the homing of lymphocytes to involved skin in patients with systemic sclerosis.