Week 2 - Bacterial cells, Immunity and Vaccines Flashcards
How does bacterial cells cause disease?
- Secretion systems
- Capsules
- Toxins
- Fimbria / pilli
How does secretion systems aid causation of disease?
- export / inject effector protein across bacterial cell wall into host cell
- proteins remodel cell cytoskeleton, promote host cell invasion + promote attachment to host cell - e.g. can inject own receptors into host for attachment of effector protein
How does fimbria / pilli aid causation of disease?
Found on outer membrane of bacterium
Allows bacterium to stick (adhesion) host cells
Aids biofilm formation + bacterium cell movement (twitching)
How does capsules aid causation of disease?
- Protects cell from phagocytosis / the immune system
- have surface charge (-ive) = can’t be engulfed by phagocytes
- mimic host cells (non-immunogenic) = no alert to immune system - Allows immune evasion (= important for invasive infections)
- causes host cell damage - Can be involved in attachment
How does toxins aid causation of disease?
Toxins damage systemic system
- Endotoxins
- released when cell dies
- part of gram -ive bacteria cell wall
- low site speciality - Exotoxins
- produced by bacterial cell
- high potency
- high site specificity (= move through body to find specific target)
- susceptible to temp.
3 Types:
1. Enzymatic - e.g. AB toxins help get enzyme into cell (A subunit ~ encodes catalytic activity, B subunit ~ binds to receptor+ translocation)
2. Pore forming - toxin attach to receptor in cell membrane + toxin experience conformational change = pore formed
- e.g. pneumolysin in CAP
3. Superantigens - activate many T-cells causing cytokine release
- force binds T-cell receptors and molecules on antigen presenting cells
How does pneumolysin (in CAP) aid causation of disease?
Inhibits mucociliary pathway
Cause macrophage death
Cause inflammatory mediated tissue disease (due to influx of neutrophils)
How are infections spread?
Airborne
Fomite (non-living)
Vertical (from parent to child)
What is innate immunity?
Ability to recognise + destroy pathogen / its product
- recognises pathogen-associated molecular patterns on pathogen
Doesn’t require previous exposure to pathogen
Microbiota (normal flora) - reduces risk of infection
What is adaptive immunity?
Acquired ability to recognise + destroy specific pathogen / its product
- recognises antigen (on pathogen)
Dependant on previous exposure to pathogen
What is natural immunity?
Natural active immunity - acquiring an infection which causes immune response
Natural passive immunity - antibody transfer through placenta / breast milk
What is artificial immunity?
Artificial active immunity - given controlled dose of antigen to induce production of antibodies (= vaccination)
Artificial passive immunity - injection of antiserum from an immune individual
How are antibodies produced?
- First exposure to virus
- WBC (B cells) recognises antigens (presented by pathogen) as foreign
- WBC produces antibodies specific to antigen (clonal selection)
- When B cell antibody binds to antigen = B cells divide = large increase in no. of B cells
- Some B cells become plasma cells (which secrete antibodies)
- Rest become memory cells
Antibodies are immunoglobulins (Ig)
How does vaccinations work?
- Antigen is introduced into body causing immune system to attack the pathogen
- Causes development of B memory cells (stored in lymph nodes)
- Encounter same antigen again already have cells to destroy it (before disease develops)
What are the main types of vaccines?
Live attenuated -
- more effective
Non-viable / inactivated -
What is the UK immunisation schedule?
Why is the immune system important for human health?
- Protects against pathogens e.g. virus, bacteria, fungi
- Provides deference
- Apoptosis / eliminates altered cells
What are the mechanisms used by the immune system to defend against infection?
- Innate immune system
(born with this)
- first line defence
- non specific (responds to all pathogens same way)
- quick onset - Adaptive immune system
(develop as grow)
- slow onset / activation
- specific
- produces memory cells
Hematopoietic Stem Cell-derived Lineages and their use
H. stem cell differentiates to form other cells
Stem cells are from bone marrow
Common Lymphoid Progenitor:
- Lymphoid cells are used in adaptive system
- lymphoid stem cells produce B cells, T cells and natural killer cells
Myeloid Stem cells:
- produce CFU cells that produced neutrophils, monocytes (differentiate further into macrophages + dendritic cells), eosinophils, basophil, mast cells, megakaryocytes + erythrocytes
Dendritic cells and their use
- Are antigen presenting cells
- Engulf antigen, break it down + present antigen on their weir cell surface
- Dendritic cells activate T-cells, which produces B cells
(innate immune system)
Macrophages and their use
-Are antigen presenting cells
- Engulf antigen, break it down + present antigen on their weir cell surface
- Activates T-cells, which produces B cells
(innate immune system)
Neutrophils and their use
- Migrate towards infection + engulf bacteria (small microorganism)
- only bacteria as pathogen has to be smaller than cell - Phagocytosis of bacteria BUT DON’T present antigen on surface
(innate immune system)
Basophil and their use
- Involved in allergic reactions
- Have receptors on surface that responds to antibodies
(innate immune system)
Eosinophil and their use
- Protect against parasites (large microorganism)
- Breaks down parasite into smaller parts = can be engulfed by macrophages, dendritic cells or neutrophils
(innate immune system)
Cytokines and their use and their use
- Toxic to viruses
(innate immune system)
Natural killer cells and their use
- Destroy virus infected cells
(innate immune system)
Mast cells and their use
- Release factors which increase blood flow = attracts cells from immune system to site of infection
(innate immune system)
Th / CD4+ cells and their use
- Macrophages activate CD4+ cells
- phagocytose / break down bacteria + present antigen on surface of Major Histocompatibility Complex (MHC) - CD4+ cells recognise antigens on Class II complex
Th (T helper cells):
Th1 = stimulates cell mediated immunity
Th2 = stimulate plasma cells + secretion of antibodies
(adaptive immune system)
Tc / CD8+ cells and their use
- Recognise antigens on Class I MHC
(adaptive immune system)
B Lymphocytes and their use
- Produce antibodies (immunoglobulin = Ig)
-B cells are induced by diff. cytokines = differentiation in B cells produced = diff. antibodies produced
Immunoglobulin:
- prevents antigen binding to host cell + infecting it
- can bind to receptor on cells + attract other immune cells
-
(adaptive immune system)
Hypersensitivity Reactions
Reaction that occurs in response to allergen e.g. pollen
Type 1:
- IgE mediated hypersensitivity
- allegers binds to receptor for IgE
- causes histamine production (i.e. sneezing, itching)
Type 2:
- IgG mediated cytotoxic hypersensitivy
Type 3:
- Immune complex mediated hypersensitivity
- causes aggregation of diff. immune complexes
- neutrophils recognise aggregation as infection = eliminate it
Type 4:
- Cell-mediated hypersensitivity
- Have proteins which activate T helper cells + produce cytokines which activate macrophages
Allergies and therapeutic strategies
Allergies:
- Anti-histamine drugs = ease allergy symptoms
- bind to histamine receptor (preventing histamine from binding)
Drug Induced Allergies:
- Drug binds to receptor forming a complex
- Complex is recognised as foreign pathogen by APC
- immunes sits is activated = T cell activation
