Immunology Flashcards
What is immunology?
is the study of the immune system, including its responses to microbial pathogens and damaged tissues and its role in disease.
What is the most important physiological function of the immune system?
prevent or eradicate infections.
What is the immune system and what does it consist of?
The immune system is the body’s defense against infectious agents and other foreign substances (antigens) in its environment, It consists of a complex network of cells, tissues, and organs ……….. Immune response (immunity)
What are the primary lymphoid organs?
BM
Thymus
What is bone marrow?
- The BM is the site of B cell maturation.
* Also, the site of generation of all blood cells from a common stem cell (hematopoiesis).
What is the thymus?
Site of T cell maturation.
What are secondary lymphoid organs?
- Include the lymph nodes and the spleen.
- Mucosa-associated lymphoid tissues including tonsils in the nasopharynx and Peyer’s patches in the sub-mucosal surfaces of the small intestine; also act as secondary lymphoid aggregates.
What is the function of secondary lymphoid organs?
Trap and concentrate antigens.
What are the cells of the immune system?
- A common lymphoid progenitor producing:
a. T lymphocytes
b. B lymphocytes
c. Natural killer (NK) cells. - A common myeloid progenitor producing:
a. Leukocytes:
b. Erythrocytes.
c. Platelets
What are immune cells that come from BM?
Lymphocytes:-
• B lymphocytes
• T lymphocytes
• NK cells
Phagocytes:-
• Macrophages
• Neutrophils
Antigen-presenting cells:-
• Macrophages
• Dendritic cells
• B lymphocytes
What is immune system discrimination?
self/non-self
Self-antigen ——> no immune response
Foreign antigen pathogen——-> immune response
How many layers does the immune system consist of?
3
What are the types of immunity?
The immune system has two lines of defense:
- Innate (non-specific) immunity.
- Adaptive (specific) immunity.
What do the innate and acquired immune systems use to sense potential threats?
The innate and adaptive immune systems utilize cell-surface receptors to sense potential threats (microbes).
What are the characters of innate immunity?
- the First line of defense against pathogens and give a rapid response.
- Nonspecific
- no memory.
- Always present in healthy individuals.
- recognize and react against microbes only……. PAMPs
What are the components of innate immunity?
- Barriers to infections
- Innate immunity cells
- Soluble defense
What are barriers to infection?
o Physical barriers: include the epidermis and mucous membranes.
o Chemical and environmental barriers:
▪ pH: the acidic pH of the skin, stomach, and vagina inhibits the growth of pathogens.
▪ Microcidal molecules: α- and β- defensins), lysozyme, RNases, and DNases that.
o Biological barriers (commensal microbes): are
microbes (like flora) that exist in a symbiotic relationship with the body. They colonize skin, GIT, upper respiratory, urogenital tracts, and eyes and inhibit the establishment of pathogenic microbes.
What are innate immunity cells?
a. Phagocytic cells: are cells having the ability to phagocytose (recognize, ingest, and
kill) microbes and any foreign antigen (phagocytosis)
• Macrophages
• Neutrophils
b. Natural killer (NK) cells: function in killing tumor cells and virus-infected cells
What are examples of soluble defense?
- The complement system.
- Cytokines of innate immunity.
- Other plasma proteins of innate immunity:
▪ Mannose-binding lectin (MBL). ▪ C-reactive protein (CRP)
What happens to the circulating levels of plasma proteins after infection?
- The circulating levels of these plasma proteins increase rapidly after infection.
- This protective response is called “acute phase response”.
What are the characters of adaptive immunity?
- Second line of defense.
- Develops as a response to infection.
- Specificity and memory are characteristic features of adaptive immunity
- Lymphocytes are the cells of adaptive immunity
Specificity of the adaptive immunity
the immune response is specific for a certain antigen Specificity ensures that different antigens elicit specific responses.
memory of the adaptive immunity
is the ability to “remember” and respond more strongly to repeated exposure to the same microbe.
What is the function of B lymphocytes?
produce antibodies that neutralize and eliminate the extracellular microbes and toxins (Humoral immunity).
What is the function of T lymphocytes?
eradicate intracellular microbes (Cell-mediated immunity).
What is another function for B and T lymphocytes?
recognize antigen by antigen-specific receptors present on their surfaces.
What are the types of adaptive immunity?
Humoral (antibody-mediated)
• B lymphocytes
Cell-mediated
• T lymphocytes
What are the sequences of adaptive immune response?
- Antigen recognition by lymphocytes receptors.
- Activation of lymphocytes leads to proliferation & differentiation into effector cells (cells that carry the function) and memory cells.
- Elimination of the microbes.
- Decline and termination of the immune responses (homeostasis) once the pathogen is eliminated to avoid damaging host tissues.
- Long-lived memory (memory cells).
What are the cells activated in innate immunity?
Phagocytes: macrophages & neutrophils and NK cells
What are the cells activated in adaptive immunity?
B lymphocytes T lymphocytes
What are the receptors in innate immunity?
Pattern recognition receptors
What are the receptors in adaptive immunity?
B cell receptor; BCR
T cell receptor; TCR
What is the complement activation in innate immunity?
Alternative & MBL pathways
What is the complement activation in adaptive immunity?
Classical pathway
What are the cytokines in innate immunity?
TNF, IL-1, chemokines, IFN-α, IFN-β, IFN-γ, IL-12
What are the cytokines in adaptive immunity?
IL-2, IL-4, IL-5, IFN-γ, IL-13, IL-17
What are the stages that a lymphocyte passes by to perform its function?
Naive —-> activated ——> effector
What are lymphocytes similar in and what are they different in?
- Morphologically similar
* heterogeneous in phenotypes and functions
What can the lymphocytes be distinguished with?
They can be distinguished by surface proteins the “CD” and a number
What are the characters of B lymphocytes?
- Developed and mature in the BM.
- B is derived from BM
- 10-15% of total blood lymphocytes
- Phenotype markers:
o Antigen receptor (BCR)
o CD19, CD21,
o Recognize any antigen e.g. proteins, polysaccharides, lipids, nucleic acids
What is the function of B lymphocytes?
humoral immunity (antibodies)
How do B lymphocytes recognize antigens?
by B cell receptor (BCR)
What are B lymphocytes stimulated with?
Stimulated by antigen leading to their proliferation & differentiation into effector cells (plasma cells) that secrete antibodies and memory B cells.
What do B lymphocytes destroy?
Microbes
What are the characters of T lymphocytes?
- “T” refers to Thymus derived
- Developed & mature in the thymus
- The majority of blood lymphocytes 75%.
- Phenotype markers: TCR, CD3, CD4, CD8.
What is the function of T lymphocytes?
cell-mediated immunity.
What are the types of T lymphocytes?
CD4 OR CD8
o Helper T cells TH (CD4+)
o Cytotoxic T cells TC (CD8+)
What are the subtypes of T lymphocytes?
- Helper T cells (CD4+) TH:
- Help B lymphocytes to produce antibodies
- Help macrophage activation to destroy ingested microbes.
- Cytotoxic T cells (CD8+) TC:
- Kill virus-infected cells.
- Kill tumor cells.
- Graft cells ….. Rejection.
- Regulatory T cells (Treg)
How do T lymphocytes recognize antigens?
Recognize antigen by TCRs
Recognize protein antigens only.
They recognize antigen only in the form of peptide fragments plus MHC molecules on the surface of APCs (MHC Restriction):
— CD4+ cells recognize peptide + class II MHC molecules.
— CD8+ cells recognize peptide + class I MHC molecules.
What is the function of the proteasome?
Degrade Proteins into Peptides.
What are the characters of NK cells?
- A third population of lymphocytes.
- 10% of blood lymphocytes.
- Cytoplasmic granules
- Phenotype markers: CD16
- Antigen receptor: KARs and KIRs.
What is the function of NK cells?
— Killing tumor cells.
— Killing virus-infected cells.
— Antibody-dependent cellular cytotoxicity (ADCC)
— Produce IFN-γ which activates macrophages.
KIRs
- Killer inhibitory receptors
* (-) signal
KARs.
- Killer activating receptors
* (+) signal
What is ADCC?
(Antibody-Dependent Cell-Mediated Cytotoxicity )
What are phagocytes?
Phagocytes are cells having the ability to phagocytose (recognize, ingest, and kill) microbes and any foreign antigen.
What are the types of phagocytes?
- Monocytes/Macrophages
2. Neutrophils
What are the characters of monocytes/macrophages?
- Monocytes circulate in blood … ingest microbes in blood
- Macrophages tissue-resident of monocytes …. Ingest microbes in
tissues
What are the characters of neutrophils?
- Polymorphonuclear leukocytes PMNs
- The most numerous leukocytes in the blood
- Increase in No. in blood …acute infection
- Ingest microbes and then die .. Pus cells
What are the steps of phagocytosis?
• Delivery of phagocytes to the site of infection:
o Diapedisis
o Chemotaxis
- Recognition of microbes
- Phagocytic adherence to the target (opsonization)
• Ingestion or engulfment of the target particle …..
Phagosome formation
- Phagolysosome formation
- Intracellular killing
What is step 1 in phagocytosis?
• Delivery of phagocytes to the site of infection:
o Diapedisis
o Chemotaxis
What is step 2 in phagocytosis?
• Recognition of microbes: phagocytes recognize microbes in blood and tissues by surface receptors specific for microbes e.g. Toll-like receptors TLRs
What is step 3 in phagocytosis?
• Phagocytic adherence to microbes.
o Opsonization: coating of the microbe by opsonin {antibody or complement C3b, C4b}
o Binding of the microbe to receptors on phagocytic cells
What is step 4 in phagocytosis?
• Ingestion (engulfment) of microbe into the cytoplasm of the cell within a membrane vesicle…………….. phagosome
What is step 5 in phagocytosis?
• Fusion of phagosome with lysosome of the cell …. Phagolysosome{digestive vesicle}
What is step 6 in phagocytosis?
• Intracellular killing
o oxygen-independent: lysosomal granules, lactoferrin, low pH, and lysosomal enzymes.
o oxygen-dependent: toxic oxygen-derived products and toxic nitrogen oxides
What are the characters of APCs?
- include dendritic cells, macrophages, and some B cells
- Present in the epithelium of the skin, GIT, respiratory tract ….. Entry of microbes
- Capture, transport, process protein antigens into peptides and present the peptides to T cells.
- They are rich in Class II MHC molecules
What is the function of APCs?
- Capture and transport antigens to peripheral lymphoid tissues
- Process antigens into pieces (peptides)
- Present peptides to T lymphocytes
What are stem cells?
Stem cells are undifferentiated (unspecialized) cells
What are the unique properties of stem cells?
o Self-renewal: numerous cycles of cell division by mitosis
o Potency = the capacity to differentiate into specialized cell types e.g. Muscle cell, Pancreatic beta-cell, Red blood cell, Nerve cell, Brain cell, Liver cell, …..etc
What are the two types of stem cells?
- Embryonic stem cells: isolated from the inner cell mass of blastocysts
- Adult stem cells: that are found in adult tissues (skin, muscles, umbilical cord blood, brain, heart, and bone marrow).
What is the medical importance of stem cells?
• Stem cell therapy ……. Cell-based therapy
• Treating patients by transplanting specialized cells that have been grown from stem cells in the laboratory (stem cell culture).
o Leukemia: Bone marrow transplants
o Cardiovascular disease: repairing damaged heart cells after a heart attack.
o Type1 diabetes mellitus: replacing damaged pancreatic beta cells with functional beta cells which can secrete insulin.
o Spinal cord injuries: damaged neurons.
o Alzheimer’s disease: replacing the damaged brain cells.
o Muscle damage.
