Innate Immunity Flashcards
Define innate immunity.
Innate immunity is the inborn resistance against infections that an individual possesses right from birth as a result of their genetic makeup, and which is non-specific.
What are nine components of innate immunity?
(1) Physical and chemical barriers
(2) Cellular components
(3) Pattern Recognition Receptors (PRRs)
(4) Inflammatory response
(5) Complement system
(6) Antimicrobial proteins and peptides
(7) Cytokines and chemokines
(8) Acute phase response
(9) Interaction with adaptive immunity
features of innate immunity
acts in minutes, prior microbial exposure is not required, diversity is limited, it is non-specific, no memory
external defenses of innate immunity
skin, mucous membranes, secretions
internal defenses of innate immunity
phagocytic cells, antimicrobial proteins, inflammatory responses, natural killer cells
functions of innate immunity
➤ recruitment of immune cells: produces chemical signals to attract immune cells to the site of infection.
➤ activation of the complement system: a group of proteins that enhance the ability of antibodies and phagocytic cells to clear microbes and damaged cells.
➤ removal of foreign substances: identifies and eliminates pathogens and debris through phagocytosis.
➤ activation of adaptive immunity: presents antigens to the adaptive immune system to help develop a more specific and long-lasting immune response.
Compare innate immunity and adaptive immunity.
➤ Innate immunity: resistance to infection that an individual possess since birth. Adaptive immunity: Resistant to infection that an individual acquires during his lifetime.
➤ Innate immunity: Immune response occurs in minutes. Adaptive immunity: Immune response occurs in days.
➤ Innate immunity: Prior exposure to the antigen is not required. Adaptive immunity: Develops following antigenic exposure.
➤ Innate immunity: Diversity is limited, acts through a restricted set of reactions. Adaptive immunity: More varied and specialized responses.
What are the primary phagocytic cells in the innate immune system?
Macrophages and neutrophils.
State the role of macrophages and neutrophils in innate immunity.
Macrophages are critical effector cells in innate immunity that engulf and digest pathogens, dead cells, and debris through phagocytosis, and they also secrete cytokines to mediate inflammation and recruit other immune cells.
Neutrophils are the most abundant white blood cells and act as the first responders to infection, rapidly migrating to sites of infection where they kill pathogens through phagocytosis, degranulation, and the release of neutrophil extracellular traps (NETs).
Macrophages and neutrophils are both crucial components of the innate immune system. Compare the two using the following criteria:
(a) Origin and development
(b) Location
(c) Lifespan
(d) Morphology
(e) Response to infection
(f) Chemotaxis
(a) Origin and development
Macrophages: Derived from monocytes, which are produced in the bone marrow and circulate in the bloodstream. When monocytes migrate into tissues, they differentiate into macrophages.
Neutrophils: Formed from hematopoietic stem cells in the bone marrow. They undergo several stages of maturation before being released into the bloodstream.
(b) Location:
Macrophages: Found in tissues throughout the body, including the liver (Kupffer cells), lungs (alveolar macrophages), brain (microglia), and skin (Langerhans cells).
Neutrophils: Primarily found in the bloodstream and are among the first cells to migrate to sites of infection.
(c) Lifespan
Macrophages: Long-lived, persisting for weeks to months.
Neutrophils: Short-lived, typically surviving for a few days.
(d) Morphology
Macrophages: Larger cells with a single, kidney-shaped nucleus and lack granules.
Neutrophils: Smaller cells with a multi-lobed nucleus and granular cytoplasm containing enzymes and antimicrobial substances.
(e) Response to infection
Macrophages: Respond more slowly to infection but are crucial for chronic infections and tissue repair.
Neutrophils: Rapid responders to infection, particularly effective against bacteria.
(f) Chemotaxis
Macrophages: Slower chemotactic response compared to neutrophils.
Neutrophils: Rapid chemotactic response, quickly migrating to infection sites.
What triggers the activation of macrophages in the initial phase of an immune response?
recognition of pathogens through engagement of PRRs
What type of cells are Natural Killer (NK) cells, and what is their role?
NK cells are lymphocytes that target and kill virus-infected cells and tumor cells without prior sensitization.
[5-minute video]: Natural Killer Cells
How do dendritic cells bridge innate and adaptive immunity?
They capture antigens from pathogens and present them to T cells, initiating an adaptive immune response.
What is the role of mast cells in the immune response?
They release histamine and other mediators to increase blood flow and attract immune cells to infection sites, and are involved in allergic reactions.
“Mast cell granules contain, among other factors copious amounts of the vasoactive amino acid histamine.” What can provoke mast cell degranulation?
(a) direct injury
(b) in response to complement components (C3a and C5a)
(c) encounter with PAMPs
(d) binding of IgE to specific mast cell surface receptors
What are the roles of eosinophils and basophils in innate immunity?
Eosinophils are effective against parasitic worms, while basophils release histamine and contribute to inflammation and allergic responses.
What is the function of monocytes in the immune system?
They circulate in the blood, migrate to tissues, and differentiate into macrophages or dendritic cells. Macrophages are highly effective at phagocytosis and dendritic cells are the most potent antigen-presenting cells.
What is the significance of NK cells not requiring prior sensitization?
It allows for a rapid immune response to virus-infected cells and tumor cells.
What are PAMPs and PRRs?
Pathogen-Associated Molecular Patterns (PAMPs) are conserved molecular motifs found on pathogens but not on host cells. The include components like lipopolysaccharides (LPS) from gram-negative bacteria, peptidoglycan from gram-positive, and viral RNA.
Pattern Recognition Receptors (PRRs) are proteins on immune cells that detect PAMPs. Examples include Toll-like receptors (TLRs) and NOD-like receptors (NLRs), which trigger immune responses to eliminate the pathogens.
What are cytokines?
Cytokines are signaling proteins released by immune cells that regulate the immune response, promoting inflammation, activating immune cells, and directing them to infection sites.
What are chemokines?
Chemokines are a subset of cytokines that specifically induce chemotaxis in nearby responsive cells.
List some examples of cytokines involved in innate immunity.
Examples include interleukins (IL-1, IL-6), tumor necrosis factor (TNF), and interferons (IFN-α, IFN-β).
Define acute phase response.
Acute phase response is a rapid inflammatory reaction triggered by infection or trauma, whereby the liver, stimulated by inflammatory cytokines like IL-1, IL-6, and TNF-α, increases its production of acute phase proteins.
Give two examples of acute phase proteins.
mannose-binding lectin, C-reactive protein
