What lymphocyte surface marker is found on memory B cells but not on memory T cells?

Memory B cells are characterized by the expression of the CD27 surface marker, which plays a crucial role in their development and function. CD27 is part of the tumor necrosis factor (TNF) receptor superfamily and is involved in the activation and survival of memory B cells. Its presence distinguishes memory B cells from naive B cells and memory T cells.

In contrast, memory T cells do not express CD27 in the same manner; they may have other markers that help define their memory state but lack CD27 as a defining feature. This distinction is important in immunology, as it helps researchers and clinicians identify and differentiate between various lymphocyte populations, particularly in understanding the immune response and in developing immunotherapeutic strategies.

The other options represent markers that have distinct roles within the immune system, but they are not exclusive to memory B cells. For example, CD45RA is associated with naive T cells rather than memory T cells specifically. CD4 and CD28 are also found on T cells but do not distinguish memory T cells from memory B cells, thereby reinforcing that CD27 is unique to memory B cells in this context.