Lecture 1 - Cells & Structure Function of Immune System Flashcards
What is innate immunity?
Google: Body’s first line of defense against germs entering the body
Involve: Epithelial barriers, phagocytes, dendritic cells, complement, NK cells
Time of activation: 0-12 hours after infection
What is adaptive immunity?
Google: Acquired immunity or specific immunity, only found in vertebrates. The adaptive immune response is specific to the pathogen presented.
Involve: B-lymphocytes, T-lymphocytes (1-3 days)** / Proliferation (3-4 days)** / Antibodies & T-cells respectively (4-7days)**
**Number of days after infection
2 types: Humoral & Cell-mediated (aka cellular)
What is humoral immunity?
B-CELLS!!!!
Microbe (i.e Extracellular microbe) → Responding lymphocytes (i.e. B-cells) → Effector mechanism (Secreted antibodies) → Transfer medium (i.e. Serum)
Function: Block infections & eliminate extracellular microbes.
What is cell-mediated immunity?
T-CELLS!!!!
2 types (CD4/CD8 T-cells)
Phagocytosed microbes in phagocytes → CD4/T-helper → binding → T-cells macrophages
Function: Activate macrophages to kill phagocytosed microbes.
Viruses → CD8/cytotoxic T-cell → binding → T-cells
Function: Kill infected cells and eliminte reservoirs of infection
Briefly describe the phases of adaptive immunity.
- Antigen recognition (0-4 days):
Still feel sick
Antigen presenting cell binds to naive T-cells
Pathogen / virus binds to naive B-cells - Lymphocyte activation (4-12 days):
Clonal expansion
Differentiation
Antibody producing cell and effector T-cells count are at their peak on the 12th day/ - Antigen elimination (12-16 days):
Elimination of antigens first through humoral immunity
Cell-mediated immunity comes next?!
Starts to feel better already. - Contraction (homeostasis) (16 days onwards):
Apoptosis of lymphocytes - Memory generation
Surviving memory cells
Back to basal level
Memory T-cells increase with age. How?
As we grow older, thymus output decreases (fewer naive T-cells made as rate of production drops)
We also encounter more variety of pathogens leading to the conversion of naive T-cells to Memory T-cells
So, we are just using up our naive T-cells reserve.
What are the features of adaptive immunity?
- Specificity
Ensures that distinct antigens elicit specific responses (imprt for vaccine development) - Diversity
Enables immune system to respond to a large variety of antigens - Memory
Leads to enhanced responses to repeated exposures to the same antigens (special1) - Clonal selection & expansion**
Increases number of antigen-specific lymphocytes from a small number of naive lymphocytes (allow for faster release of immune cells) - Specialisation
Generates responses that are optimal for defense against different types of microbes. - Contraction and homeostasis
Allows immune system to respond to newly encountered antigens
Avoid tissue damage (side effect of constant expression) + save energy - Non Reactivity to self
Prevents injury to the host during responses to foreign antigens (tolerant to host cells)
What is clonal selection?
+ Lymphocyte clones mature in generative lymphoid organs, in the absence of antigens
+ Clones of mature lymphocytes specific for diverse antigens enter lymphoid tissues
What is clonal expansion?
+ Antigen-specific clones are activated (“selected”) by antigens
+ Antigen-specific immune responses occur
What are the differences between innate immunity & adaptive immunity?
- Response Time
Innate: Mins / hours
Adaptive: Days - Specificity
Innate: Not that specific to strain but specific for molecules and molecular patterns associated with pathogens
Adaptive: Highly specific discrimination even minor difference in molecular structure, details of microbial or nonmicrobial structure recognised with high specificity - Diversity
Innate: Limited number of germ-line encoded receptors
Adaptive: Highly diverse, very large number of receptors arising from generic recombination of receptor genes (diff. B & T-cell receptors to tackle more variety of pathogens) - Memory responses
Innate: none
Adaptive: Persistent memory, with faster response of greeted magnitude on subsequent infection - Self/non-self discrimination
Innate: Perfect; no microbe-specific patterns in host (will not attack self)
Adaptive: Very good; occasional failures of self/nonself discrimination result in autoimmune disease - Soluble components of blood or tissue fluids
Innate: Many antimicrobial peptides and proteins
Adaptive: Antibodies - Major cell types
Innate: Phagocytes (monocytes, macrophages, neutrophils), natural killer cells and dendritic cells, antigen-presenting cells
Adaptive: T cells, B cells, antigen-presenting cells
List the different types of cells in the immune system. + Their localisation
All cells in the immune system arise from pluripotent hematopoietic stem cells in the bone marrow.
3 types of cells differentiation: Common lymphoid progenitor & Common myeloid progenitor & dendritic cells
a. Common myeloid progenitor →
Granulocyte / macrophage progenitor (Bone marrow)
Neutrophil (Blood)
Eosinophil (Blood)
Basophil (Blood)
Unknown precursor of mast cell (Blood) → Mast cell (Tissue)
Monocyte (Blood) → Macrophage (Tissue)
b. Megakaryocyte / erythrocyte progenitor (Bone marrow)
Megakaryocyte (Bone Marrow) → Platelets (Blood)
Erythroblast (Bone marrow) → Erythrocyte (Blood)
c. Common lymphoid progenitor → Blood → Lymph nodes → Effector cells B-cell T-cell NK cell
d. Immature dendritic cells →
Blood → Tissues → Lymph nodes
What is neutrophil?
- Mediate the earliest phases of inflammation (fastest!)
- Short-lived, function only for 1-2 days and then die
- 1st line of defense
- Activated function: Phagocytosis and activation of bactericidal mechanisms downstream.
What is eosinophil?
- Present in mucosal linings of the respiratory, gastrointestinal, and genitourinary tracts, and numbers can increase during inflammation
- Activated function: Killing of antibody-coated parasites
What is basophil?
- Low numbers in tissues, may be recruited to some inflammatory sites
- Activated function: Promotion of allergic responses and augmentation of anti-parasitic immunity
What is mast cell?
- Defense against helminths and other microbes
- Responsible for allergic reactions
- Hypersensitivity (to be elaborated)
- Activated function: Release of granules containing histamine and active agents.
What is macrophage?
+ Macrophages have two forms depending on the site of localisation (blood monocytes or activated tissue macrophage)
+ Major function of macrophages in host defense is to ingest and kill microbes via phagocytosis
Ingest dead cells – clean up process
+ Secrete cytokines to recruit more monocytes and leukocytes
+ Serve as antigen presenting cells to stimulate T-cells
+ Tissue repair by stimulating new blood vessel growth / activation of fibroblast formation
What are the functions of B-lymphocytes?
+ Neutralisation of microbe
+ Phagocytosis
+ Complement activation
What are the functions of Helper T-lymphocytes?
+ When microbial antigen presented by APC, release of cytokines
+ Lead to activation of macrophages, Inflammation, Activation of T & B-cells
What is the function of cytotoxic T-lymphocytes (CTL)?
Killing of infected cells.
What is a regulatory T-cell?
+ CD4 / cytotoxic T-cell
+ Involved in the contraction / natural process.
+ Suppression of T-cells to maintain homeostasis.
What are NK cells?
+ Killing of viral infected cells
+ Antibody-dependent cell-mediated cytotoxicity (ADCC)
+ Releases lytic granules that kill some virus-infected cells
What are dendritic cells?
+ Most important Antigen-presenting cells (APCs) for activating naive T-cells
+ Major roles in linking innate and adaptive immune responses.
What are the uses of antibodies?
+ Complement activation
+ Neutralise microbes
+ Facilitate in phagocytosis
What is the difference between small lymphocytes and lymphoblast?
+ Lymphoblast are activated small lymphocytes.
+ The nucleus becomes smaller, more cytoplasm since more proteins are made.
