21: Innate Nonspecific Host Defenses (Part B)
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- 21.1: Cellular Defenses
- The formed elements of the blood include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Of these, leukocytes are primarily involved in the immune response. All formed elements originate in the bone marrow as stem cells (HSCs) that differentiate through hematopoiesis. Granulocytes are leukocytes characterized by a lobed nucleus and granules in the cytoplasm. These include neutrophils (PMNs), eosinophils, and basophils.
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- 21.2: Pathogen Recognition and Phagocytosis
- Phagocytes are cells that recognize pathogens and destroy them through phagocytosis. Recognition often takes place by the use of phagocyte receptors that bind molecules commonly found on pathogens, known as pathogen-associated molecular patterns (PAMPs). The receptors that bind PAMPs are called pattern recognition receptors, or PRRs. Toll-like receptors (TLRs) are one type of PRR found on phagocytes.
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- 21.3: Inflammation and Fever
- nflammation results from the collective response of chemical mediators and cellular defenses to an injury or infection. Acute inflammation is short lived and localized to the site of injury or infection. Chronic inflammation occurs when the inflammatory response is unsuccessful, and may result in the formation of granulomas (e.g., with tuberculosis) and scarring (e.g., with hepatitis C viral infections and liver cirrhosis).
Thumbnail: Scanning electron micrograph of a phagocyte (yellow, right) phagocytosing anthrax bacilli (orange, left). (CC BY 2.5;
via PLOS).