P-selectin glycoprotein ligand-1 is broadly expressed in cells of myeloid, lymphoid, and dendritic lineage and in some nonhematopoietic cells

Abstract

P-selectin glycoprotein ligand-1 (PSGL-1) is a mucin-like glycoprotein ligand for P- and E-selectin on myeloid cells and a subset of lymphocytes. We used flow cytometry and immunohistochemistry to examine expression of PSGL-1 on minor leukocyte populations, differentiating hematopoietic cells, and nonhematopoietic tissues using two monoclonal antibodies to distinct protein epitopes on PSGL-1. In the bone marrow, PSGL-1 was expressed on myeloid cells from the myeloblast stage to the segmented neutrophil, but was not detected on erythroblasts or megakaryocytes. All types of circulating myeloid cells expressed PSGL-1, and PSGL-1 was retained after extravasation of myeloid cells into tissues. PSGL-1 was also expressed on circulating dendritic cells, monocyte-derived dendritic cells, dendritic cells in lymphoid tissues and epidermis, and follicular dendritic cells. All types of lymphoid cells examined expressed PSGL-1, including immature and mature thymocytes, naive and memory T cells, γ/δ T cells, natural killer cells, B cells, and CD34+ progenitor cells. However, PSGL-1 levels were substantially lower on tonsillar lymphocytes than on circulating lymphocytes, suggesting that PSGL- 1 expression is down-regulated during or after entry of lymphocytes into secondary lymphoid tissue. Although PSGL-1 antigen was detected primarily on hematopoietic cells, it was also present on the epithelium of the fallopian tube. Furthermore, PSGL-1 antigen was detected sporadically on microvascular endothelium in some pathologic tissues. This suggests that PSGL-1 may have functions other than mediating leukocyte adhesion.