Expression of the CR1 receptor on human leukemia-derived CD4+ T cell lines

The complement receptor type 1 (CR1) is a membrane glycoprotein expressed on a variety of cells including some, but not all, human T lymphocytes. The present study was designed to investigate CR1 expression on human leukemia-derived CD4+ T cell lines. The expression of CR1, as well as the complement receptor type 2 (CR2) and membrane cofactor protein (MCP), were analyzed on cells from the SUP-T1, CEM-SS, HUT-78, and MOLT-3 cell lines by flow cytometry. All four cell lines expressed CR2 and MCP, but only the SUP-T1 cell line contained CR1+ cells. Within the SUP-T1 cell line, a mean of 8.5% of the cells were CR1+. Scatchard analysis indicated that approximately 2700 CR1 molecules were expressed per CR1+ SUP-T1 cell, a value that corresponds to the quantitative expression of CR1 on normal peripheral blood T lymphocytes. Separation of CR1+ and CR1- cells within the SUP-T1 cell line by flow cytometry and subsequent reculture of the sorted cells showed that both the enriched CR1+ and the enriched CR1- cell populations returned to a mixed CR1 phenotype over time. These data suggest that SUP-T1 cells can express CR1, but only transiently. Two-color flow cytometric analysis indicated that the expression of CR1 by SUP-T1 cells did not fluctuate with the cell cycle. SUP-T1 cells were also cultured in the presence of agents known to activate T cells. Phytohemagglutinin and phorbol 12-myristate 13-acetate induced a transient increase in the percentage of SUP-T1 cells expressing CR1, compared to cells cultured in media alone. These results suggest that CR1 expression is up-regulated during T cell activation. The CR1+ SUP-T1 cell line, as well as the CR1- cell lines, may provide useful models for investigating how CR1 expression is regulated and for exploring a possible role for CR1 in the pathogenesis of AIDS.