Toll-like receptors as part of the innate immune response

There are two major arms of the immune system: innate immune response, and acquired, or adaptive, immune response. Phagocytic cells recognize pathogens that bind to specific receptor recognition molecules or through complement fixation, and then activate pathways to contain infection. Essential components of the innate immune response include neutrophils, eosinophils, natural killer cells, natural killer T cells, mast cells, cytokines, complement, and antimicrobial peptides. In the latter, T lymphocytes recognize foreign antigens presented on major compatibility complexes I and II on the cell surface of antigen-presenting cells (APCs). Lymphocytes that recognize foreign antigens then clonally expand to provide an antigen- specific immune response. More recently, another key component of the innate immune response has been discovered, the toll-like receptors (TLRs). These receptors allow the innate immune system to tailor its response depending on the stimulatory antigen and which TLR is activated. TLRs allow the innate immune system to control activation of the adaptive response, thus helping to bridge the gap between innate and adaptive immunity. The TLRs play an important role in many skin diseases.