The Host Immune System Flashcards
Adaptive Immunity
- Timeline
- First exposure, the adaptive immune response requires about TWO TO THREE WEEKS (first image, yellow line)
- The next time the pathogen is encountered, there is a massive surge of antibodies and the pathogen clears (second image)
- After a period of time, the antibodies are disbanded due to their high metabolic demand, and the T-cells maintain a ‘memory’ of pathogen to rapidly produce antibodies on the next exposure.
Biofilm
- Function
- A mechanism of immune cell evasion, and also prevents the penetration of antibiotics and other cellular factors
- Do not allow antibiotics to penetrate, don’t allow host cells to penetrate, provide a conduit for bacteria to communicate with one another
- Different bacteria can tell other bacteria what to do in a biofilm
Most bacteria in nature are found in biofilms
Biofilms
- Where?
- Special attribute
- Biofilms can grow on joints, particularly prosthetic joints
This is a virulence factor
Biolfilms
- Definition
- Secretions from bacteria
- Polysaccharide on the outside, they form everywhere
- They form when organisms stick to a surface and produce an extracellular matrix
Cell-Mediated Immunity
- Different types of cells involved
- Several different types of cells involved, including
- Cytotoxic T-cells
- Regulatory T-cells
- Natural Killer (NK) cells
- Important as a defence in combination with antibody, but may also be important alone
Components of the Innate Immune System
- Steps and Cells
- Inflammatory Response
- Cellular recruitment to the site of infection - Phagocytosis
- Ingestion of the bacteria (pac man) - Lysozyme Degradation
- Bacteria are ingested into specific vacuoles or ‘pockets’ in the cell that contain digestive enzymes (lysozyme)
Evading Host Immune Defence - Capsule Production
- Definition
- Found in
- Characteristic
- Avoids Phagocytosis
Recall macrophages
- Form a thick polysaccharide layer that resides outside of the cell
- Acts as a shield that prevents the macrophage from internalizing the bacteria, gives bacteria an innate ability to resist phagocytosis
Found in
- Strep pneumoniae
- Cryptococcus neoformans
VIRULENCE FACTOR
Evading Host Immune Response - Toxin Production
- Pathogen produces small proteins or polysaccharides that are able to arrest cellular functions or lyse host cells
Examples
- Clostridium botulitum
- C. Diff
- Staph Aureus
Can be neurotoxic, cytotoxic
Evading Host immune system
- Antigenic Drift and Shift
VERY IMPORTANT: HAPPENS IN MOST VIRUSES THAT ARE RNA
Antigenic Variation
- Dramatic changes in sequences
- H1N1 to H5N1 etc
Drift
- Gradual change in antigen
- Slower, nuanced, creates a mutation in the ANTIBODY REGION
- Kind of what happened with covid (alpha, delta, omicron)
Most of the time you get drift
Highest pathogen burden is through ____
- Eating
Host Immune System - Innate
- Definintion
- Example
- First line of defence, does not have memory
- Responds the same way REGARDLESS OF THE PATHOGEN
Eg FEVER
- Most organisms have a tight metabolic range
- Fever increases the temperature changing the (vary how annoying you want to be about this answer) effectiveness of metabolic enzymes required by pathogens
- Also occurs with injury, inflammation etc
Host Immune System - Innate
- Typical Response (with cells)
- Neutrophils, the most numerous white blood cells in the body, create the initial inflammatory response
- Macrophages then engulf pathogens and digest them
Humoral Response or Antibody-Mediated Response
Humoral Response or Antibody-Mediated Response
- Antibodies vs Antigens
- What do vaccines contain?
ANTIBODIES - Act against parts of the virus/bacteria/fungus/parasite, which are called ANTIGENS
ANTIGENS - Parts of the virus/bacteria/fungus/parasite
Vaccines contain ANTIGENS
Humoral Response or Antibody-Mediated Response
- Function of IgG
- Function of IgM
- Function of IgA
IgG
- In the body, can be transmitted TRANSPLACENTALLY
- Long lived (30, 40, 50 years)
IgM
- Short lived
- The FIRST antibody seen in response to infection
- Typically hangs around for 6-9 months and then is gone
IgA
- Secreted in mucosal membranes, or any other type of secretory cell
Humoral Response or Antibody-Mediated Response
- Types of immunoglobulins
- Very broad function
IgG
IgM
IgA
IgE
IgD
Respond to antigens (ANTIbody GENerator)
Key Difference Between Nonspecific and Adaptive Immune System (with example)
- It “remembers”
Eg H1N1 outbreak in 2009, the older population didn’t tend to get it at as high rates
- There was an outbreak in 68 and they had adapted to it
Methods of Overcoming Host Immune Defences
- Biofilms
- Capsule Production
- Toxin Production
- Antigenic Drift and Swift
Nonspecific Host Defences
- Barriers include structural, enzymatic, and pH of the environment
- Normal flora also prevent pathogens from taking a foothold and causing infection
Nonspecific Host Defences (4)
- Skin
- Waterproof, UV resistant, temp resistant, impact resistant - Fever
- Nonspecific post-breach - Mucocilliary elevator
- Pushes the mucus down towards the stomach for acid digestion - Urination
- Infection occurs through a portal of entry- Eyes
- Mouth
- Nose
- Ears
- Genital Tract
- Urinary tract
Urination helps to ‘flush out’ bacteria and the low pH helps to maintain the urinary tract
- Most concentrated immune response is through the GI-associated lymph point. Acid bath of 1.5 pH kills potential pathogens
Nonspecific Host Responses
- Cellular/Systemic (4)
- Lysozyme
- Breaks peptidoglycan - Lactoferrin
- Binds free iron, limiting bacteria from obtaining it - Secretory IgA
- Antibody in secretions - Neutrophils and Cellular Reactive Oxygen Species
- Toxic to cells
- Inflammatory recruitment
Nonspecific Host Responses
- Neutrophil Pathway (4 steps)
Pathogen Control - Cytotoxic T Cell-mediated Immunity
- Function of T-Cells
- Cytotoxic T-Cells destroy altered cells by recognizing foreign protein sequences presented on the cell surface
- Detect changes in the types of peptides presented on the pathogen cell wall.
- Can expand to large populations of clones that will contract once the pathogen has been cleared.
- A small proportion of cells will become memory cells
Three Ways of Overcoming the Host Immune Response
- tiered system
Tiered System
1. Nonspecific
2. Specific cells that remember
3. Antibodies that kill organisms
Toxins
- Endotoxin vs Exotoxin
ENDOTOXIN
- Structural components of the outer membrane of GRAM NEGATIVE bacteria
- Lipid A component of LPS
- Heat stable (cooking etc does not kill it)
Exotoxins
- Exotoxins - excreted toxins
- Enterotoxins - Exotoxin with effects in the gut
Why does UTI screening occur mid-stream?
- Get rid of what’s in the first part of the tubing and then observe what’s in the bladder
