  Immunological memory is a fundamental theory of modern immunology, which is
traditionally believed to be mediated only by B and T lymphocytes that
recognize antigen epitopes in a receptor-restricted manner. During the last
decade data accumulated to show that monocytes and macrophages, the two main
initiators of innate immune response, also built up a "memory" to antigens they
encountered, though in most concerned publications a different wording (i.e.
"train" or"educate") was utilized to describe this feature. More recently, Hole
et al demonstrated a "memory-like" response of dendritic cells (DCs). In brief,
if fungal-challenged mice could develop a protective immune response, DCs
immediately (in 3 weeks) isolated from those mice would manifest a
pro-inflammatory phenotype. Even after the mice were allowed to rest for 10
weeks, DCs from them still exhibited an enhanced immune activation profile in
their transcriptome and cytokine productions upon re-challenge with same
pathogens. Lastly, Hole showed that the "training" or memory-building in DCs
was achieved by histone modification. All above findings obtained in monocytes,
macrophages or DCs emphasized the necessity for rechecking the questions
whether antigen presenting cells (APCs) as a whole could be classified the
third class of cells that would mediate immunological memory. In this essay,
the author described the effort he made in late 1990s to identify dendtitic
cell-mediated memory, and how he named his daughter SHUYI to memorize that
hypothesis.
