Quick to remember, slow to forget: rapid recall responses of memory CD8+ T cells.

The functional roles of memory B and T lymphocytes underlie the phenomenal success of prophylactic vaccinations, which have decreased morbidities and mortalities from infectious diseases globally over the last 50 years. However, it is becoming increasingly appreciated that memory cells are also capable of mediating the pathology associated with autoimmune disorders and transplant rejection, and may pose a significant barrier to future clinical advancement in immunoregulation. Therefore, understanding the unique properties of memory lymphocytes (as compared to their naive precursors) is a major area of investigation. Here, we focus on one of those singular properties of memory T cells (T(M))-rapid recall. As will be discussed in more detail, rapid recall refers to the ability of quiescent T(M) cells to efficiently and robustly express 'effector functions' following stimulation. Studies that have advanced our understanding of T(M) cells' rapid recall using CD4(+) T cells have been expertly reviewed elsewhere, so we will focus primarily on studies of CD8(+) T cells. We will first review the different ways that CD8(+) T(M) cells can be generated, followed by discussing how this influences their functional properties in the settings of immune protection and pathology. Then, rapid recall ability will be discussed, with emphasis placed on what is currently known about the mechanisms that underlie this unique property of T(M) cells.