Читать книгу Immunology - Richard Coico - Страница 63

Now that we have outlined the origins and major characteristics of innate immune cells, we will discuss the sophisticated yet elegantly simple ways in which these cells initiate their host defense roles: pattern recognition. The underlying host defense mechanism associated with this arm of the immune system is the ability of innate cells and the specific soluble mediators they produce to recognize and respond to evolutionarily conserved microbial structures termed pathogen‐associated molecular patterns (PAMPs). Detection of PAMPs by innate immune cells occurs via soluble and cell‐associated germline‐encoded pattern recognition receptors (PRRs). It is important to note that this feature of innate immune recognition of pathogens differs markedly from recognition mechanisms associated with the adaptive immune system as illustrated in Figure 3.4.

As will be discussed in subsequent chapters, B and T lymphocytes (also called B and T cells, respectively) express somatically generated antigen‐specific receptors. Thus, these receptors are not germline encoded but rather the translational products of multiple genes that are pieced together by gene rearrangement that occurs during their development. Many PRRs are highly expressed on DCs—highly efficient APCs—where they can be located on the cell surface, in endocytic compartments, or the cytoplasm. Upon recognition of foreign antigen, particularly in the presence of PAMPs, DCs help to initiate an adaptive immune responses by B cells (which produce antigen‐specific antibody) and T cells (which express antigen‐specific T cell receptors). Adaptive responses take days to weeks to develop but last considerably longer (years) than innate responses, which are very rapid (minutes to hours) and last for a shorter time (days or weeks). In addition, in contrast with adaptive immune responses that ultimately result in the generation of clonally expanded, highly antigen‐specific memory B and T cells, activated innate immune cells do not expand or generate memory cells.

Figure 3.4. Comparison of specificity and cellular distribution of receptors used in innate and adaptive immunity.