Infectious disease Flashcards
What is infection?
What is an infectious disease?
Infection = invasion and growth of an organism in a host
Infectious disease = When an infection leads to host damage and injury
What is pathogenesis?
What is a pathogen?
Pathogenesis = the mechanism by which a disease is produced
Pathogen = disease causing organism e.g. bacteria
What is a communicable disease?
What is a zoonotic disease?
Communicable = disease that can be spread from one person to another
Zoonotic = Disease spread from animals to humans
What are primary pathogens?
What are opportunistic pathogens?
Primary pathogens = cause disease in someone even if they have a fully functioning immune system
Opportunistic pathogens = take the opportunity to cause disease when the immune system is weakened
What is the principle behind Koch’s postulates and what are the 4 Koch’s postulates
Principle = figuring out which organism caused the disease
- Pathogen must be found in all hosts with the disease but not in healthy individuals
- The pathogen must be isolated from a diseased host and be able to be grown in pure culture
- When given to a healthy individual, the pathogen must reproduce the disease of the original case
- The pathogen can be isolated and grown in pure culture from the newly-infected host
What do fimbriae/pili do on bacteria and what is pilin variation?
Finger like projections, allow the bacteria to adhere to the host cell
Pilin variation = Bacteria contain different pili that could be expressed, but only one type of pili is actually expressed
Through the course of infection, the bacteria can vary the type of pili protein expressed to a different type at random, preventing the immune system from recognising the different pili proteins
(diagram in jotter)
What is virulence?
The severity of disease caused by the pathogen
What are virulence determinants and what are the 2 types?
Virulence determinants = component of the bacteria that has the ability to harm the host
2 types:
- Extracellular determinants = products made and secreted by the bacterial cell
- Cell surface determinants = determinants that are held on the surface of bacteria
What are exotoxins and what are the 3 classes of exotoxins, including what effect each class has?
Exotoxins = secreted toxins (extracellular determinants)
Classes:
- Neurotoxins = damages the neurons/nervous system
- Cytotoxins = kills the cell
- Enterotoxins = harms the intestines and digestive system
What are the 2 main parts to exotoxins and what are they responsible for?
- B part = binds the exotoxin to the host cell
- A part = is active and responsible for the specific toxic effects
What are exoenzymes and what do they do?
Work more locally by degrading the tissue to promote the spread of the bacteria deeper into the tissue
What type of bacteria are endotoxins found on?
What are endotoxins also referred to as and what are the 3 distinct regions, including what their functions are?
Gram-negative
Lipopolysaccharides (LPS)
Contains:
- O-polysaccharide chain = specific to the species of gram-negative bacteria its found on (O-specific chain)
- Lipid A = hydrophobic molecule which anchors the whole LPS molecule to the cell surface of the target cell. Also educes the toxic activity to the target cell (different effects depending on the structure of this part
- Core = links the O-specific chain and Lipid A parts together
What do our cells do in defence of an endotoxic infection? (4)
- Our cells activate macrophages, which release cytokines
- Cytokines activate complements
- Compliments activate the coagulation cascade
- This causes local inflammation and swelling to occur
What is sepsis and what does this cause (5)?
When the LPS (endotoxins) spreads from the local inflammation to the rest of the body
Causes fever, vasodilation, hypotension, thrombosis, and organ failure which leads to death
What are the 4 big differences between exotoxins and endotoxins?
Table in jotter
Chemical nature :
Exotoxins = proteins which can be denatured
Endotoxins = LPS
Location (on bacteria):
Exotoxins = Extracellular, secreted
Endotoxins = Cell surface attached
Potency (damaging effect):
Exotoxins = Relatively high
Endotoxins = Relatively low
Type of bacteria found in:
Exotoxins = Both gram-positive and gram-negative
Endotoxins = Just gram negative
What is innate immunity?
What are 2 examples of innate immunity components? (just names)
Non-specific first line of defence, always present and acts quick. Acts the same way each time.
Phagocytic cells and complement
What are 2 examples of phagocytic cells?
How does phagocytosis work (include examples 2 of phagocytic receptors)? (3)
Examples = Macrophages and Neutrophils
- Cell have pattern recognition receptors to recognise “foreign” molecular patterns from pathogens (recognises when a foreign molecule binds to the receptor) - including C3b and Fc receptors
- Cell holds the pathogen in a vacuole and a reactive oxygen species/enzymes are released into the vacuole to destroy the pathogen
- Danger signals are also released to attract more immune cells to the site of infection
What is compliment?
How is the signal amplified?
Family of enzymes that are present in blood as an inactive precursor
Become active upon stimulation by a signal
Initial small signal can simulate many molecules through a positive compliment cascade
What are the 3 pathways that active compliment and how does each activate the compliment?
What is the active enzyme formed called?
What are the 3 outcomes of this?
Classical = Antigen/antibody complex
Alternative = Surface of pathogen
Lectin = Mannose sugar on pathogen surface
Active enzyme = C3 Convertase
Outcomes:
- Vascular permeability is increased to recruit immune cells to site of infection
- Opsonization = coats foreign organisms in compliment protein to help phagocytes recognise the organism as foreign and engulf it
- Membrane Attack Complex (MAC) = punches hole in the pathogen membrane, causing lysis of the pathogen (destroys it)
Diagram of this on summary sheet
What is adaptive immunity?
What are the 2 molecules involved in adaptive immunity?
Specific, second line of defence, takes longer to develop and produces a quicker response on second exposure (memory)
B Cells - Antibodies
T cells - Helper cells (cytotoxic/regulatory cells)
What does the variable region of B-cells (antibodies) contain?
What does the constant region determine and what are the 4 different types?
How does the antibody change during the course of infection, and what does this depend on?
Variable region = VDJ recombination, random combinations of segments of the V, D, and J genes join together to make the variable part specific
Constant region determines the class of antibody
3 Classes:
- IgM, always the first antibody produced in the immune response
- IgA
- IgE
-IgG
Class switches from IgM to IgG, IgE, or IgA
Depending on the environment the B cell is in (on the type of infection)
What do T cell receptors recognise and what are these?
What type of receptors on which molecules recognise which class of MHC?
What does the class of MHC indicate?
Recognise surface markers: MHC and processed antigens displayed on the surface of infected cells
CD8 receptors on T Cytotoxic (Tc) cells recognise MHCI
CD4 receptors on T helper cells (Th) cells recognise MHCII
Class of MHC indicates the peptide origin and helps for an appropriate response to be initiated
(all on summary sheet)
What type of cells produce MHCI surface signals and how are they produced?
All nucleating cells
Cytosolic proteins, including intracellular pathogens, are degraded to peptides via the proteosome.
These peptides then bind to MHCI on the surface of the cell, and the peptide-MHCI complex acts as a cell surface marker to indicate the cell is infected
(on summary sheet)
What response is initiated when Tc cells recognise MHCI surface markers?
Tc cells kill the infected cell by inducing apoptosis through the use of perforin, granzymes and FAS ligands
(On summary sheets)
