Introduction to Immunology Flashcards
1
Q
Define the term “immunology”
A
Immunology = the study of the immune system
- provides defence or IMMUNITY against INFECTION
- distinguishes between SELF and NON-SELF, reacts against NON-SELF (simplification e.g. gut microbiome)
- May also recognise DANGER signals caused by damage to cells and tissues (e.g. stroke, cancer)
- immune system can react to this
2
Q
Describe the key characteristics of the innate and adaptive immune system
A
- Innate - evolutionarily ancient
- Broad specificty
- Not affected by prior contact
- Immediate/rapid response (hrs)
- (all organisms have some form of innate immunity)
- Adaptive - evolved 500 million years ago in jawed fish
- Highly specific
- Enhanced by prior contact
- Slow response (days-weeks) for effective adaptive immune response
- Both primarily involve white blood cells (leukocytes) + soluble factors
3
Q
What are the 4 main factors of the innate immune system
A
- Barriers (physical (e.g. skin), chemical)
- Soluble proteins (complement, interferons etc.)
- Local and systemic responses (inflammation - local, fever - systemic)
- Leukocytes (phagocytes, NK cells)
4
Q
What are the main factors of the adaptive immune system
A
- B and T lymphocytes
- B cells respond by secreting soluble antibodies: HUMORAL immunity )
- T cells develop into cytotoxic T cells (kill infected cells) or helper T cells (secrete cytokines that act on other cells): CELL-MEDIATED immunity
- Both B and T cells can develop into MEMORY cells
5
Q
How does the body recognise infection?
A
ADAPTIVE:
- B and T lymphocytes express specific antigen receptors
INNATE?
- Charles Janeway 1989: proposed the existence of Pattern Recognition Receptors (PRRs) that recognise Pathogen Associated Molecular Patterns (PAMPS) on cells of the innate immune system.
- PAMPS a.k.a. MAMPS (microbe associated molecular patterns) (e.g. LPS, peptidoglycan)
- Unique to microbes
- Conserved
- Essential for microbe survival (often)
6
Q
Describe the receptors of the innate leukocytes
A
- Myeloid cells:
- e.g. neutrophils, eosinophils, basophils, mast cells, marcophages, dendritic cells have →
- Broad specificity PRRs that recognise MAMPS
- NK cells: recognition through recognising altered “self”
- i.e. host cells infected with viruses or intracellular bacteria
- PRRs and altered self receptors are generally expressed by all leukocytes of a particular type
- Genes coding for PRRs inherited in the germline
- Limited number (relatively limited number of PRRs)
7
Q
Describe the clonal selection hypothesis
A
- B cell as example:
- Hypothesised that each B cell has its own specific receptor when “born”, upon binding to antigen → this B cell is “selected” and division is encouraged rapidly, and multiply and differentiate into plasma cells which secrete soluble antibodies specific to that antigen
- from a single B cell you can develop 100’s/1000’s of B cells with the same specificity to a specific antigen
- Memory B cells developed as well. Able to divide and differentiate upon re’infection of same bacteria/virus
- recognised a danger that you could accidentally make antibodies that recognise own cells → these are deleted
7
Q
Describe the receptors of adaptive leukocytes
A
- Adaptive
- B and T lymphocytes: highly specific antigen receptors
- B cell receptor (membrane form of antibody
- T cell receptor
- Clonally expressed
- meaning: isolating a particular B or T cell it will have just 1 type of receptor on its surface that recognises just 1 particular foreign molecule
- Genes assembled “at random” during lymphocyte development
- > 10^9 specificities (many)
8
Q
Describe the pros and cons of innate immunity
A
- Small number of inherited PRRs recognise MAMPs unique to microbes
- Good at distinguishing between self/non-self
- Non-clonal activation
- Potential for collateral damage to self (immunopathology) (damage caused by immune system)
9
Q
Describe the pros and cons of adaptive immunity
A
- “infinite” number of randomly generated antigen receptors
- Cannot reliably distinguish between self/non-self or between harmful/innocuous material results in autoimmune disease
- usually control mechanisms stop these developing
- Clonal activation
- very specific response
- Targets immune response specifically towards infection, sparing uninfected tissues
10
Q
How do lymphocytes meet antigen? Situation: you step on a rusted nail infested with bacteria
A
- First cells likely to recognise bacteria are Phagocytes called macrophages aswell as dendritic cells (found primarily in skin but also in secondary lymphoid tissues)
- Bacteria taken up by macrophages and dendritic cells
- can then travel through draining lymphatic vessels into secondary lymphatic tissue
- Naive B and T cells found in secondary lymphatic tissues
- Macrophage or dendritic cells present bacteria to B and T cells → B and T cells stimulated
- usually T cell required to be stimulated → divide and differentiate
- Clonal expansion occurs in lymph node
- Plasma cells produce antibodies
- T cells cytotoxic and helper → do their thing
10
Q
Describe the lymphoid tissues and how they are organised and they key areas of it
A
-
Primary lymphoid tissue (yellow on picture) (thymus and bone marrow)
- lymphocytes reach maturity, acquire their specific receptors
- all lymphocytes develop in the bone marrow. T cells reach maturity in thymus, B cells reach maturity in bone marrow
- Then they can go into the blood, tissues etc. and return through lymphatics into aggregations of tissue called secondary lymphoid tissues
-
Secondary lymphoid tissue:
- mature lymphocytes are stimulated by antigen
- i.e. lymph nodes
- Usually in secondary lymphoid tissue, the lymphocytes recognise antigen and undergo clonal selection and expansion etc.
- Mature “naïve” lymphocytes traffic between blood and the lymphatic system, but infections can occur anywhere.
- naive = lymphocytes that just recieve their receptor in bone marrow (B cell) or thymus (T cell)
