Dendritic cells also phagocytose and function as anti

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Dendritic cells also phagocytose and function as anti- gen-presenting cells (APCs) and act as important mes- sengers between innate and adaptive immunity. Mast cells and basophils share many salient features with each other and both are instrumental in the initiation of acute inflammatory responses, such as those seen in allergy and asthma. Unlike mast cells, which generally reside in the connective tissue surrounding blood ves- sels, basophils reside in the circulation. Eosinophils are granulocytes that possess phagocytic properties and play an important role in the destruction of parasites that are too large to be phagocytosed. Along with mast cells and basophils, they also control mechanisms associated with allergy and asthma. NK cells (also known as large granu- lar lymphocytes [LGLs]) play a major role in the rejec- tion of tumours and the destruction of cells infected by viruses. Destruction of infected cells is achieved through the release of perforins and granzymes from NK-cell granules which induce apoptosis (programmed cell death) [4]. The main characteristics and functions of the cells involved in the innate immune response are sum- marized in Figure 1. Innate immunity can be viewed as comprising four types of defensive barriers: anatomic (skin and mucous Cell Image % in adults Nucleus Functions Lifetime Main targets Macrophage* Varies Varies x Phagocytosis x Antigen presentation to T cells Months – years x Various Neutrophil 40-75% Multi-lobed x Phagocytosis x Degranulation (discharge of contents of a cell) 6 hours – few days x Bacteria x Fungi Eosinophil 1-6% Bi-lobed x Degranulation x Release of enzymes, growth factors, cytokines 8-12 days (circulate for 4-5 hours) x Parasites x Various allergic tissues Basophil < 1% Bi- or tri-lobed x Degranulation x Release of histamine, enzymes, cytokines Lifetime uncertain; likely a few hours – few days x Various allergic tissues Lymphocytes (T cells) 20-40% Deeply staining, eccentric T helper (Th) cells (CD4+): immune response mediators Cytotoxic T cells (CD8+): cell destruction Weeks to years x Th cells: intracellular bacteria x Cytotoxic T cells: virus infected and tumour cells x Natural killer cells: virus-infected and tumour cells Monocyte 2-6% Kidney shaped Differentiate into macrophages and dendritic cells to elicit an immune response Hours – days x Various Figure 1 Characteristics and function of cells involved in innate immunity [1,3,4]. *Dust cells (within pulmonary alveolus), histiocytes (connective tissue), Kupffer cells (liver), microglial cells (neural tissue), epithelioid cells (granulomas), osteoclasts (bone), mesangial cells (kidney) Warrington et al . Allergy, Asthma & Clinical Immunology 2011, 7 (Suppl 1):S1 Page 2 of 8
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membrane), physiologic (temperature, low pH and che- mical mediators), endocytic and phagocytic, and inflam- matory. Table 1 summarizes the non-specific host- defense mechanisms for each of these barriers.
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  • Spring '18
  • Dr. Omare
  • allergic reaction, Asthma & Clinical Immunology

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