1.2 Innate immunity: First line of defense
2 min read•july 25, 2024
is our body's , acting fast to protect us from invaders. It's like a security system that's always on, using , chemicals, and special cells to keep us safe.
Our and are like fortress walls, while stomach acid and act as chemical weapons. When trouble strikes, kicks in, calling for backup and starting the healing process.
Physical and Chemical Barriers
Characteristics of innate immunity
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- Innate immunity forms first line of defense against pathogens present from birth providing non-specific response to invaders
- Key characteristics include rapid response within minutes to hours no immunological memory and evolutionarily conserved mechanisms across species
- Components encompass physical barriers (skin, mucous membranes) (, enzymes) cellular components (, ) and humoral components ()
Physical and chemical immune barriers
- Physical barriers include skin with stratified squamous epithelium and keratin layer mucous membranes lining respiratory gastrointestinal and urogenital tracts and cilia in respiratory tract trapping particles
- Chemical barriers comprise low pH and antimicrobial sebum on skin surface mucus trapping pathogens and containing antimicrobial proteins stomach acid (HCl) enzymes like lysozyme in tears and saliva pepsin in stomach and antimicrobial peptides (, )
Role of inflammation in immunity
- Inflammation triggered by tissue damage or pathogen detection characterized by cardinal signs (redness, heat, swelling, pain)
- involve vasodilation increased blood flow and vascular permeability
- Cellular responses include and
- released and
- Functions encompass pathogen containment tissue repair initiation and adaptive immune system activation
Complement system in innate defense
- Complement system network of plasma proteins activated in cascade manner through classical alternative or lectin pathways
- Functions include of pathogens of immune cells and formation of (MAC)
- Key complement proteins and play crucial roles in cascade
- Regulation by prevents host tissue damage
- Complement deficiencies lead to increased susceptibility to infections and autoimmune disorders (systemic lupus erythematosus)
Key Terms to Review (29)
Acids: Acids are substances that donate protons (H+) in a solution, resulting in an increase in hydrogen ion concentration. They play a crucial role in various biological processes and act as one of the first lines of defense in innate immunity by creating an environment that can inhibit microbial growth. The ability of acids to lower pH can contribute to the maintenance of homeostasis and protection against pathogens.
C3: C3 is a central component of the complement system, which plays a crucial role in the immune response by promoting opsonization, inflammation, and cell lysis. It exists in an inactive form in the bloodstream and becomes activated during the complement activation pathways, leading to its cleavage into C3a and C3b, which have distinct biological functions in the immune defense mechanism.
C5: C5, or complement component 5, is a protein that plays a crucial role in the immune response by being a part of the complement system. It is involved in both innate and adaptive immunity, helping to promote inflammation, opsonization, and cell lysis, making it a key player in the body’s first line of defense against pathogens.
Cathelicidins: Cathelicidins are a family of antimicrobial peptides that play a crucial role in the innate immune response. They are produced by various cell types, particularly neutrophils and epithelial cells, and function as part of the first line of defense against pathogens. These peptides have broad-spectrum antimicrobial activity, targeting bacteria, viruses, and fungi, while also participating in inflammatory responses and wound healing.
Chemical barriers: Chemical barriers are substances produced by the body that play a crucial role in the innate immune system by providing protection against pathogens. These barriers function as the first line of defense, helping to neutralize or inhibit the growth of microbes and preventing them from entering the body. They include various antimicrobial peptides, enzymes, and secretions that create an inhospitable environment for harmful invaders.
Chemical Mediators: Chemical mediators are signaling molecules that play crucial roles in the immune response by facilitating communication between cells during inflammatory and immune reactions. These mediators can promote or inhibit various biological processes, influencing the outcome of immune responses and helping to coordinate the body’s defense mechanisms against pathogens.
Chemotaxis: Chemotaxis is the movement of cells towards or away from a chemical stimulus, often used by immune cells to locate sites of infection or inflammation. This process is crucial for the functioning of the immune system, as it directs leukocytes to areas where they are needed most to fight off pathogens and initiate repair processes.
Complement proteins: Complement proteins are a group of proteins that play a crucial role in the immune system by helping to identify and eliminate pathogens. These proteins work together in a cascade of reactions known as the complement system, enhancing the body's ability to fight infections and trigger inflammatory responses. Their actions include opsonization of pathogens, formation of the membrane attack complex, and promotion of inflammation, linking them closely to both innate immunity and the inflammatory response.
Complement regulatory proteins: Complement regulatory proteins are molecules that control the activation and function of the complement system, a crucial component of innate immunity that helps the body recognize and eliminate pathogens. These proteins ensure that complement activation is kept in check to prevent damage to host tissues while still allowing for effective immune responses against invading microorganisms. They play a critical role in maintaining the balance between immune defense and self-tolerance.
Cytokines: Cytokines are small signaling proteins that are crucial for cell communication in the immune system. They play an essential role in mediating and regulating immunity, inflammation, and hematopoiesis, linking innate and adaptive immune responses.
Defensins: Defensins are small cationic peptides that play a vital role in the innate immune system by exhibiting antimicrobial properties against bacteria, fungi, and viruses. They are produced by various cell types, including epithelial cells and leukocytes, and act as a first line of defense by disrupting microbial membranes and neutralizing pathogens. Defensins are essential for maintaining host defense mechanisms and contribute significantly to the overall response of the innate immune system.
Enzymes: Enzymes are biological molecules, primarily proteins, that act as catalysts to accelerate chemical reactions in living organisms. They play a crucial role in various metabolic processes, including digestion and energy production, and are essential for maintaining homeostasis within the body.
Factor B: Factor B is a protein that plays a crucial role in the alternative pathway of the complement system, which is an essential part of the innate immune response. It helps to activate the complement cascade when pathogens are detected, enhancing the body's ability to fight infections. Factor B works by binding to C3b, allowing for its cleavage by Factor D, which generates the C3 convertase enzyme that amplifies the immune response against invading pathogens.
First line of defense: The first line of defense refers to the initial barriers and mechanisms that protect the body from pathogens and harmful substances, forming a crucial part of the innate immune response. These defenses act as the body's primary shield against infection and are essential for maintaining overall health and preventing disease. They include physical, chemical, and biological factors that work together to thwart the entry of invaders.
Histamine: Histamine is a biogenic amine that plays a crucial role in the immune response, particularly during allergic reactions and inflammatory processes. It is released by mast cells and basophils, leading to various physiological effects, such as vasodilation and increased permeability of blood vessels, which are vital in the first line of defense against pathogens and allergens.
Inflammation: Inflammation is a biological response of the immune system to harmful stimuli, such as pathogens, damaged cells, or irritants. It serves to protect the body by initiating healing processes, recruiting immune cells to the site of injury or infection, and facilitating the removal of harmful agents. This complex response can be acute or chronic and is crucial for maintaining homeostasis and defense mechanisms.
Innate Immunity: Innate immunity is the body's first line of defense against pathogens, providing immediate but non-specific protection through physical barriers and immune cells. This system acts quickly to identify and respond to threats without the need for prior exposure, playing a crucial role in overall immune function and interacting with other components of the immune system to mount an effective response.
Leukotrienes: Leukotrienes are lipid compounds that are produced by immune cells and play a critical role in inflammatory responses, particularly in the context of allergic reactions and asthma. These mediators are derived from arachidonic acid and function by promoting bronchoconstriction, increasing vascular permeability, and attracting immune cells to sites of inflammation, thus influencing both innate immunity and allergic responses.
Macrophage Activation: Macrophage activation refers to the process by which macrophages, a type of immune cell, undergo changes that enhance their ability to respond to pathogens and tissue damage. This activation is crucial for the innate immune response, enabling macrophages to effectively phagocytize (engulf and digest) foreign substances, secrete cytokines, and present antigens to T cells, thereby linking innate and adaptive immunity.
Macrophages: Macrophages are large immune cells that play a crucial role in the body's defense mechanisms by engulfing and digesting cellular debris, pathogens, and foreign substances. They originate from monocytes in the blood and are pivotal in both the innate and adaptive immune responses, acting as key players in inflammation, antigen presentation, and tissue repair.
Membrane Attack Complex: The membrane attack complex (MAC) is a structure formed on the surface of pathogen cells, primarily by the complement system, that creates pores in the membrane, leading to cell lysis and death. This complex plays a crucial role in the innate immune response, providing a means for the body to directly eliminate invading microorganisms as part of the first line of defense against infections.
Mucous membranes: Mucous membranes are protective linings that cover various cavities and surfaces within the body, such as the respiratory, gastrointestinal, and urogenital tracts. They play a critical role in innate immunity as part of the first line of defense, serving to trap pathogens and foreign particles while also providing a barrier against infection. Mucous membranes secrete mucus, which not only lubricates surfaces but also contains antimicrobial substances that help neutralize threats.
Neutrophil recruitment: Neutrophil recruitment is the process by which neutrophils, a type of white blood cell, are attracted to sites of infection or injury in the body to carry out their immune functions. This process is crucial as it represents one of the first responses of the innate immune system, acting quickly to combat pathogens and initiate healing. Neutrophils play a pivotal role in the early defense against infections and their effective recruitment ensures that these cells can respond promptly to inflammatory signals.
Neutrophils: Neutrophils are a type of white blood cell that plays a vital role in the innate immune response, acting as the first line of defense against invading pathogens. They are essential for responding quickly to infections, especially bacterial and fungal, and are characterized by their ability to migrate to sites of inflammation and infection through the bloodstream and tissues.
Opsonization: Opsonization is the process by which pathogens are marked for destruction by immune cells, making them more recognizable to phagocytes. This enhances the efficiency of the immune response by promoting the binding of these pathogens to immune cells, facilitating their ingestion and elimination. Opsonization connects to various immune mechanisms, including innate immunity, antibody function, antigen-antibody interactions, and complement activation pathways.
Physical Barriers: Physical barriers are the first line of defense in the immune system, acting as a protective shield against pathogens and harmful substances. These barriers include structures and mechanisms that prevent entry of microbes into the body, such as skin, mucous membranes, and various secretions. By blocking pathogens from entering the body, physical barriers play a critical role in maintaining overall health and supporting immune responses.
Prostaglandins: Prostaglandins are lipid compounds that have hormone-like effects in various tissues throughout the body. They are derived from fatty acids and play a crucial role in mediating inflammation, regulating immune responses, and facilitating communication between cells. Their production is often triggered by injury or infection, linking them directly to the body's response mechanisms and influencing both acute and chronic inflammatory processes.
Skin: Skin is the largest organ of the body, serving as a protective barrier that separates the internal environment from the external world. It plays a crucial role in innate immunity by acting as the first line of defense against pathogens, physical damage, and harmful substances, while also participating in the immune response through various cells and processes.
Vascular changes: Vascular changes refer to the modifications in blood vessel function and structure that occur in response to injury or infection. These changes are crucial in the immune response as they facilitate increased blood flow, permeability, and the recruitment of immune cells to affected tissues. By adjusting blood flow and vessel permeability, vascular changes play a significant role in inflammation and the overall effectiveness of the first line of defense against pathogens.