F. Immunology (1) Flashcards
What is immunology?
● Immunology is the branch of biology that focuses on the study of the body’s defense mechanisms against infections and threats posed by cells within the body.
What is the immune system composed of? (3)
The primary or central lymphoid organs are the bone marrow and the thymus.
The bone marrow is responsible for producing myeloid cells, natural killer cells, B lymphocytes, and T lymphocytes.
The thymus is where immature precursor cells of T lymphocytes migrate from the bone marrow and complete their development.
What is Innate immunity? (3)
● Innate immunity is the initial response of the host to an infection.
It serves as the first line of defense.
Innate immunity involves a combination of anatomical barriers and associated factors.
What are the physical barriers? (2)
The physical barriers include the epithelium of the skin, respiratory tract, intestinal tract, and urogenital tract.
These barriers possess mechanical, biochemical, and microbial factors that prevent the entry of pathogens. For example, the skin acts as a physical barrier, while the secretion of tears, mucous secretions, and antimicrobial substances provide additional protection.
What happens if these barriers are breached?
Innate immune cells have receptors that recognize common components found in the walls of pathogens or microbes, such as lipopolysaccharides, mannose, or
complement/antibodies that opsonize the pathogen. These receptors are not specific to a particular microbe but rather recognize components that are common to many different microbes.
● Innate immune cells can be divided into two main categories:
Those that phagocytose and kill invading pathogens, and those that kill infected cells of the body.
The former category includes macrophages, neutrophils, basophils, mast cells, eosinophils, and dendritic cells. These cells can ____ and _____ pathogens or release granules that are toxic to the invaders.
engulf
destroy
The latter category comprises natural killer cells, which recognize infected cells _____ intracellular viruses or bacteria and eliminate them.
harboring
Receptors for pathogen surface components or molecules released from dying or damaged cells: (2)
Mannose Receptor: Recognizes mannose, a sugar molecule commonly found on the surface of pathogens.
Lipopolysaccharide (LPS) Receptor: Binds to lipopolysaccharides, which are molecules present on the outer membrane of certain bacteria.
● Receptors for opsonins: (3)
Fc Receptors (FcR)
Complement Receptors (CR)
Pattern Recognition Receptors (PRRs)
What are Fc Receptors (FcR)?
These receptors recognize the Fc (constant) region of antibodies. Antibodies, produced by B cells in response to pathogens, can bind to specific antigens on the surface of the pathogens. When antibodies attach to pathogens, the Fc region becomes accessible for binding to Fc receptors on immune cells. This process, known as opsonization, marks the pathogen for phagocytosis by immune cells.
What are Complement Receptors (CR)?
Complement is a group of proteins that can bind to pathogens and enhance their clearance. Complement receptors on immune cells recognize specific complement proteins, such as C3b, bound to the surface of pathogens. This binding triggers various immune responses, including phagocytosis.
What are the types of Pattern Recognition Receptors (PRRs)? (2)
✔ Toll-like Receptors (TLRs)
✔ Nod-like Receptors (NLRs)
What are ✔ Toll-like Receptors (TLRs)?
These receptors recognize specific molecular patterns associated with pathogens, known as pathogen-associated molecular patterns
(PAMPs). TLRs can detect molecules like lipopolysaccharides, flagellin, and viral RNA. When TLRs bind to PAMPs, they initiate immune responses to eliminate the pathogens.
What are ✔ Nod-like Receptors (NLRs)?
NLRs recognize molecules released by damaged cells, known as damage-associated molecular patterns (DAMPs). DAMPs are released
during cell stress, injury, or cell death. Examples of DAMPs include ATP and uric acid. NLRs can trigger immune responses to remove the sources of cellular damage.
What is Phagocytosis?
● Phagocytes, including macrophages, neutrophils, dendritic cells, and eosinophils, play a crucial role in protecting the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. This process is called phagocytosis.
● Phagocytosis is a form of endocytosis, where the phagocyte binds to the pathogen or microbe via specific receptors on its surface.
What is the full process? (7)
- In addition to the oxidative burst, phagocytes also employ oxygen-independent mechanisms to kill and degrade pathogens. These mechanisms involve the release of
enzymes and toxic molecules within the phagolysosome. Enzymes such as lysozyme, nucleases, proteases, glycosidases, lipases, phosphatases, and sulphatases degrade the pathogens or antigens, breaking them down into smaller, harmless components. - Once the pathogens or microbes are degraded, the remaining indigestible and residual material is removed from the phagocyte through exocytosis.
What is the Complement?
● Complement is a group of proteins that are produced by the liver and circulate in the blood as part of the innate immune system. These proteins play a crucial role in the defense against infections.
Complement:
What happens when an infection occurs? (2)
● When an infection occurs, complement pathways are activated. Activation can be initiated through various mechanisms, such as the binding of antibodies to pathogens or the direct recognition of pathogen-associated molecular patterns (PAMPs) by complement proteins.
● Once activated, the complement proteins are cleaved into smaller fragments, which carry out different functions.
● Some of the functions of complement fragments include: (5)
Chemo-attraction
Opsonization
Membrane attack complex (MAC) formation
Complement activation
Acute phase
What is Chemo-attraction?
Fragments such as C3a and C5a act as chemo-attractants, attracting immune cells to the site of infection. These fragments help recruit and activate other immune cells, enhancing the immune response.
What is Opsonization?
The fragment C3b acts as an opsonin. It can bind to the surface of pathogens, coating them and marking them for recognition and engulfment by phagocytic cells. Opsonization facilitates the clearance of pathogens by phagocytes.
What is the Membrane attack complex (MAC) formation?
The complement proteins C5b, C6, C7, C8, and multiple copies of C9 can assemble to form the membrane attack complex (MAC). MAC creates a pore or channel in the cell membrane of pathogens or microbes, leading to cell lysis. This pore disrupts the integrity of the pathogen’s membrane, resulting in its destruction.
What is the Complement activation?
Complement activation is an essential component of the immune response and works in coordination with other immune cells and mechanisms to eliminate pathogens. It helps initiate inflammation, enhance phagocytosis, and directly destroy the pathogens.