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.