Maturation of the immune response

The innate immune system depends on features like extracellular and intracellular pattern recognition receptors (PRR) that recognize general molecular patterns. Different types of PRR have been described, identifying microbe-, pathogen-, and danger-associated molecular patterns (abbreviated as MAMP, PAMP, and DAMP, respectively). PRR enhance ligation and phagocytosis of microbes or have signaling ability allowing activation of the cell. Ligation of extracellular toll-like receptors (TLR) by bacterial ligands like lipopolysaccharide (LPS) (binds to TLR4), peptidoglycan (PGN) (TLR2), and flagellin (TLR5) results in MyD88-dependent production of inflammatory cytokines like interleukin (IL)-1ß, IL-6, IL-8, and partly TNF-a. The expression of TLRs is vast as they are found on the cell membranes of innate immune cells (dendritic cell (DC), macrophages, natural killer cells), cells of the adaptive immunity (T and B lymphocytes), and nonimmune cells (epithelial and en ..