Immunobiology of the tonsils and adenoids

This chapter describes the distribution of immunocompetent and accessory cells in various locations of the palatine and nasopharyngeal tonsils. The chapter compares their numbers and function in aging and chronic infection, and reviews the development of B cells in the lymphoid follicles and crypt epithelium. The paired palatine tonsils and the unpaired nasopharyngeal tonsils (often called adenoids) are located in the strategic areas of the oropharynx and nasopharynx, respectively. In healthy young children, the tonsillar germinal centers support a significant proliferation of memory/effector B cells. Such expanding clones may generate precursor cells that partly terminate locally as extrafollicular immunocytes and partly migrate as J-chain-positive IgA plasmablasts via the general blood circulation to secretory effector sites of the upper respiratory tract. Evidence suggests that primed tonsillar B cells may reach such distance sites as the urogenital tract. The tonsillar germinal centers characteristically gives rise to T-cell-dependent B-cell responses and are associated with: clonal expansion of B cells, somatic hypermutation of the B-cell Ig variable (IgV) region genes, positive selection of B cells that are able to receive antigen-specific signals by high-affinity FDC-Ig interactions, subsequent differentiation to memory B cells and plasma cells of various isotypes, and induction of the J-chain gene in a variable subset of B cells.