The role of B7 family costimulatory molecules and indoleamine 2,3-dioxygenase in primary Sjögren's syndrome and systemic sclerosis.

B7 costimulatory molecules are present on antigen-presenting cells (APCs) and influence intracellular expression of indoleamine 2,3-dioxygenase (IDO), a molecule with important immunoregulatory functions. We determined the frequency of activated (CD11b+) monocytes expressing B7-1, B7-2, B7-H1, and B7-H2 molecules, and that of CD3+ and CD4+ T cells expressing the corresponding CD28, CTLA-4, PD-1, and ICOS receptors in peripheral blood samples of 20 healthy adults and 9 SSc and 15 pSS patients using flow cytometry. We also examined the intracellular expression of IDO. The expression of CD28 was lower in both SSc and pSS patients. The frequency of CTLA-4 was increased in pSS. The expression of ICOS, a stimulator of T cell activation, was elevated in pSS, but not in SSc, while that of its corresponding costimulatory molecule, B7-H2, was strongly decreased in SSc compared to controls. The frequency of PD-1 expressing T lymphocytes was decreased in both pSS and SSc. The frequency of IDO-expressing APCs, as well as intracellular IDO content in T cells was higher in pSS than in controls. Our investigation identified a number of differences in B7 costimulation between SSc and pSS patients which may play a role in the distinct pathogenesis and clinical features of these autoimmune disorders.