Human antigen presenting cells commonly express CD4 but the significance of this phenomenon has not been clarified. We analyzed a panel of Epstein–Barr virus‐immortalized B cells (so called lymphoblastoid cell lines, LCL) by using flow cytometry, DNA‐microarray analysis, and reverse transcriptase‐polymerase chain reaction (RT‐PCR). The number of CD4+ cells varied from cell line to cell line but expression of CD4 was detected by flow cytometry and RT‐PCR in all investigated cell lines. To characterize CD4 expressing LCL in more detail, we separated CD4+ and CD4− cells from single cell lines by using immunomagnetic beads. When we cultured sorted CD4+ and CD4− cells, we observed that CD4 expression was stable for several passages. However, the number of CD4+ cells decreased with time in culture. We never observed that CD4− cell lines returned back to a CD4+ phenotype. DNA‐microarray analysis of isolated CD4+ and CD4− cells indicated that the overall gene expression profile of both cell populations was highly similar. In addition, CD4+ and CD4− cells showed the same allostimulatory capacity. CD4+ LCL showed a slightly increased interleukin‐16 induced chemotaxis. Differences in the gene expression profile of CD4+ and CD4− cell lines suggested that loss of CD4 expression occurred during a differentiation step involving achaete–scute complex homolog‐like 1.
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