To clarify possible associations of decay-accelerating factor (DAF, CD55), expressed on circulating lymphocyte subsets and other hematologic cells, with corresponding cytopenias observed in primary Sjögren's syndrome (SS).
DAF expression on peripheral blood (PB) cells was determined in 21 patients with SS and 11 healthy controls by single or 2 color flow cytometry.
In the PB from SS patients, anemia, monocytopenia, neutropenia, and lymphocytopenia were observed. Compared to the controls, the percentages of DAF-negative cells were higher in CD4+ and CD8+ T cell subsets from SS patients, but the expression of DAF was similar in the other PB cells, including CD19+ B cells, CD56+ NK cells, monocytes, granulocytes, and erythrocytes. The percentages of DAF-negative cells among the CD4+ and CD8+ cells were positively correlated in SS patients, but the numbers of cells in both subsets were decreased in those patients being treated with prednisolone. However, these proportional changes are thought to reflect a decrease in the numbers of DAF-positive CD4+ and CD8+ cells, because the absolute numbers of circulating DAF-positive CD4+ and CD8+ cells, but not DAF-negative cells, were significantly decreased in SS patients. In addition, DAF-negative cells were detectable in both CD45RA+ (naive) and CD45RO+ (memory) T cells from healthy individuals, and the expression of DAF was remarkably increased in both subsets after in-vitro activation with concanavalin-A.
DAF-negative cells are proportionally increased among circulating CD4+ and CD8+ T cells in SS patients, although such changes are due to decreased numbers of DAF-positive cells within each subset. When considering previous observations, the DAF-negative CD4+ and CD8+ cells probably belong to activated T cell subsets in both SS patients and controls. However, the patterns of DAF expression seemed to be different between activated T cells recognized in the PB, and those induced by in vitro-stimulation.