Which of the following cell markers is characteristic for memory T cells?

Memory T cells are a specific subset of T cells that are essential for long-term immune memory. The characteristic marker for memory T cells is CD27, which plays a crucial role in their development and maintenance. CD27 is a costimulatory molecule that is expressed on T cells, and its presence helps to distinguish memory T cells from other T cell populations.

Memory T cells can be either CD4+ or CD8+ T cells, which are indicated by the other markers mentioned—CD4 for helper T cells and CD8 for cytotoxic T cells. While CD28 is another important costimulatory molecule associated with T cell activation, it is expressed on naive T cells as well, and its expression can diminish during T cell differentiation into memory cells. Therefore, while CD27 is specific to memory T cells, CD28 is less definitive for identifying memory status.

This specific association of CD27 with memory T cells allows immunologists and clinicians to identify and analyze these important immune cells, which are vital in providing a rapid and effective response upon re-exposure to previously encountered antigens.