1. Infection and immunity overview Flashcards
What are the types of microorganisms / infectious agents?
Unicellular:
- viruses
- bacteria
- Fungi
- Yeast
- Protozoa
Multicellular:
- Helminths (worms)
Agents:
- Prions
Define pathogens
Pathogens - microorganisms / infections agents that cause disease
What are the ‘big-three killers’ infectious diseases?
‘Big-three killers’ infectious diseases:
- Malaria
- HIV/AIDS
- TB
What is a communicable / non-communicable disease?
Communicable - infectious
Non-communicable - non-infectious
What is the sign that healthcare has been improving in preventing communicable diseases?
The # of deaths from communicable diseases has decreased recently - healthcare is improving - neonatal communicable conditions show largest decrease
How has the COVID-19 pandemic influenced deaths from the ‘big-three’ infectious diseases?
COVID-19 has impaired management of the ‘big-three’ infectious diseases:
- co-infections: in combination with COVID-19 - more deaths
- resources: more allocated to fight COVID-19 - less for ‘big-three’ - more deaths
What wider impacts do infectious diseases have?
Cause widespread societal and economic impacts on quality of life:
- lost working days
- disability
- food industry
- physical and psychological suffering
What are the types of pathogens by their inhabiting environments?
- Environmental: water, soil
- Live in hosts: humans, animals, insects, plants
What are the types of pathogen transmission?
- Physical contact
- Ingestion
- Inhalation
- Via vectors (ex mosquitoes)
How are pathogens adapted to exploit the host’s functions of life?
Pathogens exploit host’s functions of life sites for transmission - have adapted to break barriers - major diseases (ex pneumonia, COVID-19, TB)
Are all microorganisms pathogenic?
No, human micriobiome - symbiotic relationship
What are the beneficial functions of microbiome?
- digestion
- protection against pathogens
- synthesis of nutrients and vitamins
What types of processes make pathogens harmful?
- Microbe-specific caused problems to the organism
- Host-specific caused problems - because of immune response (ex inflammation)
Why high pathogenicity is not a good pathogen survival strategy?
High pathogenicity would kill the host - pathogens need to replicate + transmit -> better to be mid pathogenic to exploit
What are the broad categories of pathogen adaptations for a successful infection?
- Site specific: ability of a pathogen to colonize and infect a particular tissue or organ within a host - ex: HIV targets immune cells that express CD4 receptors and chemokine receptor CCR5
- Host specific: ability of a pathogen to adapt to and exploit the unique characteristics of a particular host species - ex: production of toxins or virulence factors that target specific host tissues or organs - Vibrio cholerae produces cholera toxin that targets the intestinal epithelial cells of humans
What are the types host-specific adaptations of pathogens?
- Intra-host: ignored by immune system at one anatomical site but reacted at another
- Inter-host: can cross species barrier - disease in one host but not another (zoonotic infections)
What is zoonosis and reverse zoonosis?
Zoonosis - inter-species transmited infection spread from animal to human
Reverse zoonosis - inter-species transmited infection spread from human to animal
75% of newly emerging infections are zoonosis - jump species barrier - humans and animals share common ecosystem
Why does Ebola not cause disease in bats?
Inter-host adpatation - Ebola causes disease in humans but not bats because:
- constitutive interferon activity fights infection (innate immunity) (Interferons - group of signaling proteins - critical role in innate immune response - act by inducing an antiviral state in neighboring cells to prevent viral replication and spread)
- very large naive antibody sets which limit viral replication (adaptive immunity)
How can pathogens be inter-host adapted?
- Pathogen adaptation itself: result of selective pressures + transmission opportunities - determine viral evolution - genetic mutations/host switching/environmental changes
- Pathogen adaptation to specific host: more adapted to the immune response - changes in receptor binding/immune evasion strategies/replication and transmission strategies/host range and tropism
What is CFR? What is its problem?
Case fatality rate (CFR) - measures severity of disease by defining a number of deaths from total number of infections
- CFR usually not uniform in all population due to age, sex, other factors
What’s the importance of Edward Jenner’s work?
First vaccine in modern Western world - innoculation with cowpox (virus similar to variola virus) - resistance against smallpox
Types of vaccines based on pathogen parts contained:
- Live-attenuated: weakened pathogen
- Dead: dead pathogen
- Subunit: surface protein
- Viral vectors: engineered harmless microorg to deliver pathogenic component
What could be a cause of immune system dysregulation?
Too little exposure to pathogens - immune system expects to be challenged
What are the examples of diseases associated with dysregulation of the immune system?
Autoimmune diseases:
- Asthma (harmless substances inhaled - inflammation in airways - hard to breath)
- Crohn’s disease (imm syst attacks healthy tissues in gastrointestinal tract - inflammation and tissue damage)
What are the good and bad roles of the immune system?
Good:
- controlling infections
- killing tumours
Bad:
- Immune pathology (autoimmune diseases, allergies)
- Graft rejection
- Metabolic diseases, mental health (?)
What are the challenges the immune system faces?
- detecting various pathogens
- distinguishing between harmful (pathogens) and harmless (food, pollen) substances
- rapidly responding and eliminating pathogens using appropriate mechanism
- controling the strength of the response
What are the example diseases which affect the immune system?
- Acquired immune deficiency syndrome (AIDS) - deletes helper T cells
- Severe-combined immunodeficiency (SCID) - born with genetic defect - bone marrow doesn’t produce T and B cells (treatment - bone marrow transplant)
What organ environments use what barriers of defence mechanisms to prevent infections?
How can pathogens break the skin barrier?
- wounds / burns
- insect bites
- animal bites
- parasites burrow through skin
What are the types of immunity? Main characteristics
- Innate immunity: rapid, not specific
- Adaptive immunity: slower, very specific, memory
How does the infection rate change depending on absence of innate or adaptive immunity?
What are the functions of innate immunity?
- senses infection - instantly responds
- communicates infection to other innate / adaptive immunity cells
- recruits immune cells to infection sites (inflammation)
- communicates to adaptive immunity when to respond + how
- cellular + biochemical pathogen killing mechanisms
What are the killing mechanisms of innate immunity?
Mechanisms act rapidly + non-specifically to provide immediate protection against a wide range of pathogens:
- Phagocytosis
- Complement system (complement proteins cause pathogen cells to lyse)
- NK cells (cytotoxic granules - when released also harms the tissue
- Antimicrobial peptides
What cells make up adaptive immunity?
B and T cells
What is the broad functions of B and T cells in adaptive immunity?
Recognise specific antigens - makes adaptive immunity more effective than innate
Why is adaptive immunity slow?
It takes time to identify and expand T and B cells for that pathogen
What makes adaptive immunity more efficient than innnate?
- high antigen specificity
- immune memory
What are the types of T cells? What are their functions?
- Helper T cells (Th cells)
- Regulatory T cells (Treg cells)
- Cytotoxic T cells (CTL)
What is the function of B cells?
To produce antibodies
What is immune memory?
Explain how innate and adaptive immunities cooperate
What are cytokines? What are their properties?
Cytokines - chemical messengers in immune system communication
What are the means used by the immune system to communicate?
- Cytokines
- Cell to cell contact
Explain how cell to cell contact helps communication in the immune system
What are the sites where immune cells meet and where immune responses are coordinated?
- Lymph nodes
- Spleen
Why do lymph nodes increase upon infection?
Because lymph nodes are the focal points to immune cell communication + initiate adaptive immunity response
Explain the full sequence of events of the immune system fighting an infection
What are the characteristics of an effective antibody?
Characteristics of antibodies (produced by B cells):
- are highly specific to pathogens
- can neutralise pathogen molecules
- can mark pathogens for destruction
- can link innate and adaptive killing mechanisms
