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.
Acute phase proteins are a group of proteins produced by the liver in response to inflammation and activation of immune cells such as macrophages and neutrophils. These proteins are part of the acute phase response, which is a rapid and nonspecific reaction to infection, injury, or inflammation.
Two examples of acute phase proteins are:
✔ C-reactive protein (CRP)
✔ Mannose-binding lectin (MBL)
What is ✔ C-reactive protein (CRP)?
CRP binds to bacterial and fungal cell walls, activating complement and enhancing phagocytosis. Elevated levels of CRP in the blood are a marker of inflammation and infection.
What is ✔ Mannose-binding lectin (MBL)?
MBL recognizes specific sugar molecules on the surface of pathogens and triggers the complement cascade. It acts as an opsonin and enhances phagocytosis.
What is the adaptive immune response? (2)
● The adaptive immune response is a specific and highly targeted response mediated by lymphocytes, including B lymphocytes and T lymphocytes.
● This response is characterized by the recognition of unique receptors on each lymphocyte that are specific for either a peptide associated with a major histocompatibility complex (MHC) protein (T cell) or an epitope on the pathogen or microbe (B cell).
● The adaptive immune response consists of the following components: (4)
B lymphocytes (B cells)
T lymphocytes (T cells)
Memory cells
Secondary lymphoid organs
What are B lymphocytes (B cells)?
B cells possess a B cell receptor (BCR) on their surface. Each B cell has a unique BCR that recognizes a specific epitope on a pathogen or microbe. When a BCR binds to its corresponding antigen, the B cell is activated.
What are T lymphocytes (T cells)?
T cells have a T cell receptor (TCR) on their surface. The TCR recognizes peptides presented by MHC proteins on the surface of antigen-presenting cells.
T cells can be further classified into two main types:
✔ CD8 T cells (cytotoxic T cells)
✔ CD4 T cells (helper T cells)
What are ✔ CD8 T cells (cytotoxic T cells)?
CD8 T cells are involved in directly killing infected cells. They recognize and bind to antigens presented by MHC class I
molecules on the surface of infected cells, leading to the destruction of the infected cells.
What are ✔ CD4 T cells (helper T cells)?
CD4 T cells play a crucial role in coordinating and regulating immune responses. They recognize antigens presented by MHC class II molecules on the surface of antigen-presenting cells and provide help to other immune cells.
What are Memory cells?
Memory cells are also produced during the adaptive immune response. These cells are long-lived and retain the ability to recognize specific antigens.
What are Secondary lymphoid organs?
Secondary lymphoid organs, including lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT), play a crucial role in the adaptive immune response.
What are Secondary lymphoid organs?
Secondary lymphoid organs, including lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT), play a crucial role in the adaptive immune response.
✔ Lymph nodes serve as sites where _______ meet antigen-presenting cells carrying engulfed pathogens or microbes.
lymphocytes
What is the function of the spleen?
✔ The spleen traps pathogens or microbes present in the blood and activates naive lymphocytes.
What is the function of the spleen?
✔ The spleen traps pathogens or microbes present in the blood and activates naive lymphocytes.
What is the function of MALT?
✔ MALT, found in mucosal tissues such as tonsils, Peyer’s patches, and the appendix, allows resident dendritic cells to engulf pathogens entering through the mucosa and activate naive lymphocytes in the mucosal compartments.
What is the innate immune system? (3)
● The innate immune system is the body’s first line of defense against infections.
● It is a non-specific immune response that provides immediate protection upon encountering
pathogens.
● The innate immune system recognizes common patterns associated with pathogens and triggers a response to eliminate them.
Immune system:
● It includes _______ barriers, chemical defenses, and various immune cells.
physical
What are barriers? (2)
● These are physical barriers of the body that serve as the first line of defense against pathogens.
● The skin acts as a protective barrier that prevents the entry of microorganisms.
What are the types of epithelia? (3)
- Respiratory epithelia
- Intestinal epithelia
- Urogenital epithelia
What is Respiratory epithelia?
● Respiratory epithelia line the respiratory tract and help filter out pathogens from the air we
breathe.
What is Intestinal epithelia?
● Intestinal epithelia line the intestines and play a role in preventing the invasion of harmful
microorganisms from the gut.
What is Urogenital epithelia?
● Urogenital epithelia line the urinary and reproductive tracts, providing a barrier against pathogens.
What are the functions of neutrophils? (4)
● Phagocytosis
● Killing Mechanisms
● Neutrophil Extracellular Traps (NETs)
● Cytokine Release
How do neutrophils function in phagocytosis? (3)
Neutrophils can recognize pathogens through various receptors, including Toll-like receptors (TLRs).
They can engulf and destroy pathogens through phagocytosis.
Neutrophils also have receptors for opsonized antigens, which are antigens marked with antibodies or complement proteins.
How do neutrophils function as killing mechanisms? (3)
After engulfing the pathogen, neutrophils use oxygen-dependent and oxygen-independent mechanisms to kill pathogens.
Oxygen-dependent mechanisms involve the production of reactive oxygen species (ROS) that have antimicrobial effects.
Neutrophils can also release antimicrobial substances, such as defensins and lactoferrin, from their granules.
How do neutrophils function in Neutrophil Extracellular Traps (NETs)? (2)
Neutrophils can release their chromatin (DNA and histones) along with antimicrobial molecules, forming neutrophil extracellular traps (NETs).
NETs can trap and kill pathogens, particularly those too large to be engulfed.
How do neutrophils function in Cytokine Release?
Neutrophils can secrete cytokines, including interferon-gamma (IFNγ), which plays a role in
macrophage activation and increased expression of major histocompatibility complex (MHC) proteins.
What are Eosinophils? (2)
● Eosinophils are a type of white blood cell involved in the immune response against parasites, particularly helminths (worms).
● They have toxic granules and can release reactive oxygen species (ROS) and other highly toxic substances to kill extracellular parasites.
Extravasation (Movement from Blood to Tissues)
● It involves a series of steps: (4)
Antibody-Dependent Cellular Cytotoxicity (ADCC)
What is the process? (5)
What is the process of activating of the classical pathway? (4)
What is the process of activating of the Lectin Pathway? (5)
What is the process of activating of the Lectin Pathway? (5)
What is the process of activating the alternative pathway? (7)
How does B cell development begin? (4)
What happens to the light chain of the BCR?
What happens to the light chain of the BCR?
