Immunology - basis of infection and immunity Flashcards
What is a Eukaryote?
Organisms incl. animals, plants, fungi, protists and algae.
What are the features of a eukaryote cell?
Has a nucleus and other membrane bound organelles.
Can be single celled or multicellular.
What is a prokaryote?
Bacteria and archaea
What are the features of a prokaryote?
Lacking a nucleus and a lot of other organelles. Often have a cell wall and a simple chromosome.
Single cell mostly
What are Saprophytes?
Prokaryotes that feed on dead and decaying matter
What are symbionts?
Prokaryotes that live with another organism and mutually beneficial
What are commensals?
Prokaryotes that live in association with another organism, adversely affecting said host
What are parasites?
Prokaryotes that require a host and are detrimental to said host
How is a pathogen defined?
An organism that will cause disease to a host
What is virulence?
The severity of the disease
What is an obligate pathogen?
Also called a primary pathogen.
Infection is ALWAYS associated with the pathology aka if the organism is there the disease will be very likely present
What is an example of a primary pathogen?
Brucella abortus - causes abortion/premature births
What is an opportunistic pathogen?
Also known as a secondary pathogen.
it is found on the epithelium of an organism but isn’t a commensual. It will become pathogenic if the opportunity present e.g. if there is a break to the epithelia
What is an example of an opportunistic pathogen?
Mannheimia haemolytica (pasteurella) - the bacteria isolated from the respiratory disease in cattle and pneumonia in calves.
What are the routes of infection?
Direct/indirect contact (skin infections)
Aerosol (respiratory)
Oro-faecal (enteric)
Vector born (requires an intermediate or transport host)
Transplacental (vertical)
What is an exogenous site of infection?
Epithelial surfaces
e.g. skin, respiratory tract, GIT and urogenital tract
What is an endogenous site of infection?
Body tissue
e.g.
Intracellular - cytoplasm
Extracellular - tissue fluid
Vesicular - endosomes
What infects intracellularly?
Viruses
What infects extracellularly?
Most bacteria and helminth parasites
What infects vesicular?
Mycobacteria and some protozoan parasites
What are the immune cells of the blood and of the tissues?
White blood cells and macrophages respectively
What types of white blood cells are there?
Neutrophils, Eosinophils, Monocytes/macrophages and lymphocytes
What do neutrophils do?
Phagocytose bacteria
What do eosinophils do?
Kill parasites
What do monocytes/macrophages do?
Kill parasites
What do lymphocytes do?
Anti-viral defence and assist other immune cells
What is Kochs postulates?
Its a method of establishing if a pathogen is responsible for a specific disease.
- The pathogen must be present in every case of the disease
- The pathogen can be isolated from the diseased host and grown in culture.
- This culture grown pathogen can be inoculated into a host.
- This pathogen can then be isolated from inoculated host
What is a prion?
Smallest type of pathogen.
It’s an infectious protein misfolded with no nucleic acid
How does a prion infect a host?
The misfolded protein exposure leads to misfolding in the body of the host
What are examples of prion infection?
Scrapie in sheep
BSE in cattle
CJD in humans
What is a enveloped virus?
A virus with a lipid membrane around it, obtained from the host cell via the cellular membrane.
What are the features of enveloped viruses?
Less virulent
What is a non-enveloped virus?
Cells without a membrane
What are features of a non-enveloped virus?
Method of penetration for entering the host cell.
More resistant to pH, heat, dryness and disinfectants
What is the life cycle of a virus?
-The virus attaches to a host cell and penetrates it
- Once in the cytoplasm it uncoats and replicates
- It synthesises viral mRNA, either directly or using the hosts, and does this to synthesise proteins for new capsids and a new viral nucleic acid.
- Capsids form around the nucleic acid and the virus is released by cytosis (if non-enveloped) or budding (forming an envelope).
What are the two immune responses of the host to viral infections?
Neutralising antibodies
Killer T lymphocytes
How do neutralising antibodies work to respond to viral infections?
They bind to the external surface of viruses, preventing attachment to cells.
How do killer T lymphocytes work to respond to viral infections?
Seek out and destroy virus infected cells, and kill them before replication is completed
What is the life cycle of bacteria?
Colonisation>Invasion>Replication>Dissemination via lymphatics/blood stream
What is the basic structure of a bacterium?
A capsule with a flagellum surrounding the cell wall containing DNA and ribosomes.
What types of bacteria are there?
Cocci (circle)
Bacillis (oval or round tubes)
Others - corkscrew, filimentous, or spirochete
What is a gram positive bacteria?
Lack an outer membrane, but surrounded by peptidoglycan which is thicker than the gram negative wall.
What is a gram negative bacteria?
Has an outer membrane of lipopolysaccharide and a thinner peptidoglycan cell wall
What type of fungi are there?
3 major groups of fungi:
- multicellular filamentous moulds
- macroscopic filamentous moulds forming large fruiting bodies aka mushrooms
- single celled microscopic yeasts
How do invasive bacteria cause disease?
Localised via abscesses etc
Systemically via speticaemia etc
How do endotoxigenic bacteria cause disease?
The bacterial endotoxin, produced from cell wall degradation, is released into the blood stream leading to toxic shock
How do exotoxigenic bacteria cause disease?
The bacteria itself secretes harmful toxins such a botulism or tetanus
How does the body respond to fungi/bacteria?
Phagocytosis
Complement activation
Opsonising antibodies
What is opsonising?
make (a foreign cell) more susceptible to phagocytosis
How do the fungi/bacteria become phagocysted?
Neutrophils and macrophages
How is complement activation achieved?
Via natural anti-microbial molecules
What is an opsonising antibody?
It coats the bacteria, leading to enhancement of phagocytosis and complement activation
What are endoparasites?
Parasites such as helminths (worms) or protozoa (small single celled)
What are ectoparasites?
Parasites such as arthropods (insects and arthropods)
What is a direct life cycle?
Spreads directly from host to host like fleas
What is an indirect life cycle?
Spread from intermediate host to final host e.g. tape worm
Or uses a vector to go bloodstream to bloodsteam e.g. Leishmania and a biting insect
How does the body respond to parasitic infection?
IgE antibodies
Eosinophils
Mast cells
How do IgE antibodies work against parasites?
Bind to surface receptors of eosinophils and mast cells allowing them to stick to the parasite, where they degranulate and spread enzymes onto it
How do eosinophils work against parasites?
Regulator of inflammation and can destroy parasites
How do mast cells work against parasites?
First line of defence with granular proteins
