Innate Immunity Overview
- Definition
- Innate immunity represents the body's initial defense mechanism against pathogens, characterized by its non-specific nature and constant level of action, regardless of previous exposure to the pathogen.
- Characteristics
- Non-specific: Targets general pathogens rather than specific ones.
- Immediate Response: Acts immediately upon encountering pathogens without prior sensitization.
- No Memory: Does not improve in efficiency after the first encounter with a pathogen.
- Mechanisms of Innate Immunity
- External Defenses (Barriers):
- Physical Barriers:
- Skin provides a tough barrier.
- Mucous membranes and their secretions trap pathogens, preventing adherence to epithelial cells.
- Mechanical actions like the flushing effect of tears, saliva, and urine, as well as mucociliary clearance in airways, remove pathogens.
- Chemical Barriers:
- Acidic environment in the stomach and fatty acids on the skin deter pathogen survival.
- Biological Barriers:
- Normal skin flora competes with pathogens, and certain microbes secrete bactericidal agents.
- Internal Defenses:
- Humoral Components:
- Lysozymes in blood plasma and interstitial fluid break down bacterial cell walls.
- Blood clotting at injury sites prevents pathogen spread.
- The complement system, akin to the clotting system, involves a cascade of plasma proteins that enhance the ability to clear microbes and damaged cells.
- Cellular Components:
- Leukocytes (White Blood Cells):
- Phagocytes:
- Neutrophils: Small, short-lived cells with a segmented nucleus, restricted to the bloodstream.
- Macrophages: Larger, long-lived cells with a non-segmented nucleus, found in various tissues.
- Dendritic Cells: Specialized antigen-presenting cells that activate the adaptive immune system.
Mononuclear-Phagocyte System
- Overview
- The mononuclear-phagocyte system consists of monocytes in the bloodstream that settle in tissues and differentiate into macrophages. These macrophages are known by different names depending on the tissue they reside in.
- Mechanisms
- Pathogen Recognition: Phagocytes use pattern recognition receptors, such as Toll-like receptors, to identify general carbohydrate profiles on pathogen surfaces.
- Phagocytosis: After recognition, the phagocyte engulfs the pathogen, forming a phagosome that fuses with lysosomes to destroy the pathogen through oxygen-dependent and oxygen-independent mechanisms.
- Extracellular Killing
- Function: Targets pathogens too large for phagocytosis.
- Cells Involved:
- Eosinophils: Attack and kill parasites through degranulation.
- Natural Killer (NK) Cells: Induce apoptosis in infected or dysfunctional body cells.
Inflammation
- Definition
- Inflammation is the local activation of innate defense mechanisms (both cellular and humoral) triggered by injury or infection.
- Symptoms
- Pain
- Heat
- Redness
- Swelling
- Loss of function
- Mechanisms
- Initial Trigger: Mast cells and basophils in the affected area release inflammatory mediators upon activation.
- Mediator Effects: