Infection and immune system overview Flashcards
What infections make up the big 3 ?
tuberculosis, HIV/AIDS, Malaria
What are the impacts to infectious diseases ?
Co-infections (multiple species of pathogen infect), healthcare resources, wider impacts (socio-economic, quality of life, morbidity (illness), mortality (death))
What are ways to acquire infection ?
- Environmental – soil and water
- Other hosts
- Physical: contact, ingestion, inhalation or a vector
- Mucosal sites
- Abrasions, cuts
How can microbes be beneficial ?
Beneficial functions include digestion of food, protection of pathogenic bacteria, synthesis of nutrients and vitamins
What makes microorganisms harmful ?
- Microbe-specific (virulence factors)
- Host-specific (inflammation)
- Microorganisms can adapt to their host or vica-versa (high pathogenicity is not a good survival strategy)
How can a microorganism adapt ?
o Adaptations can be site-specific or host specific (intra-host or inter-host)
Intra-host: different microbiome in different sites in one host
Inter-host: difference between people
Zoonoses and reverse zoonoses ?
- Zoonoses: disease spread from animals to humans
- Reverse zoonoses: humans to animals
Host-pathogens adaptations
- Innate immunity: fruit bats suppress viral infections
- Adaptive immunity: antibody repertoires are large in bats, meaning they don’t require rapid affinity maturation for limiting viral replication
What can mutations do to a microorganism ?
Virus mutations are random and can enhance transmission, virulence or immune evasion, depending on selective pressures and opportunities (including human behaviour)
What are some zoonotic pandemics ?
Zoonotic pandemics: H1N1 (1918-20), HIV (1981-), SARS CoV-1 (2002-04), H1N1 (2009), MERS CoV (2012-), Ebola (2014-16), Zika virus (2016-17), SARS CoV-2 (2020-)
What is CFR ?
Case fatality rate (CFR): proportion of deaths in a population of cases
How have we co-evolved with pathogens ?
We have co-evolved with microorganisms: our immune system expects challenges and may become dysregulated if not exposed to microorganisms, the absence of microorganisms may cause more disease than the presence (we can be too clean)
- Immunotherapy and probiotics
What are the key functions of the immune system ?
Immune system functions: controlling infections, killing tumours, immune pathology (allergies, autoimmunity), graft rejection (barriers to transplantation), metabolic diseases (obesity), mental health
What is SCID ?
SCID (Severe-combined immunodeficiency) – individuals born with a defect in T and B cells have severely impaired immune responses, and if untreated with die within a year
What are some mechanical barriers ?
- Skin: epithelial cells joined by a tight junction, longitudinal flow of air or fluid.
- Gut: epithelial cells joined by a tight junction, longitudinal flow of air or fluid.
- Lungs: epithelial cells joined by a tight junction, movement of mucus by cilia
- Eyes/nose/oral cavity: epithelial cells joined by a tight junction, tears nasal cilia
What are some chemical barriers ?
- Skin: fatty acids, beta-defensins lamellar bodies cathelicidin
- Gut: Low pH, enzymes (pepsin), alpha-defensins (cryptdins), regll (lecticidins), cathelicidin
- Lungs: pulmonary surfactant, alpha-defensins cathelicidin
- Eyes/nose/oral cavity:lysozymes in tears and saliva, histatins, beta-defensins
What is an example of microbiological barriers ?
Normal microbiota
What is the mucosal barrier ?
respiratory tract (sinus, trachea, lungs), gastrointestinal tract (oral cavity, esophagus, stomach, pancreas,intestine), urogenital (uterus, bladder, vagina), lacrimal glands (tears), salivary glands, mammary glands, reproductive tracts
- Pathogens that can evade the mucosal tract: Placenta (HIV), Lungs (influenza), STD (herpesvirus), tapeworms (food)
Match these to either innate or adaptive ?
Mast cells
B cells
macrophages
T cells
Dendritic cells
basophil
natural killer cells
eosinophil
neutrophil
CD4+ cells
granulocytes
complement proteins
CD8 cells
INNATE:
Mast cells
macrophages
Dendritic cells
basophil
natural killer cells
eosinophil
neutrophil
granulocytes
complement proteins
ADAPTIVE:
B cells
T cells
CD4 cells
CD8 cells
What does the graph look like for duration of infection against number of microorganisms for lack of innate and adaptive vs normal ?
Lack of innate: sudden and severe increase in microorganisms
Lack of adaptive: normal number of microorganisms to a normal infection but then starts to increase rather than decreases
Normal: increase then decrease
Innate gives a chance for adaptive to develop
Functions of innate immunity ?
Sense and responds to danger signals (infection and damage)
Always on, always ready to responds instantly
Communicates danger to other cells of innate and adaptive immunity
Recruits immune cells to infection site (inflammation)
Tells adaptive immune cells when to respond
Cellular and biochemical killing mechanisms
Innate killing mechanisms
phagocytosis (macrophages, neutrophils), secretion of cytotoxic granules (destructive chemicals), killing of infected cells, complement proteins
Functions of the adaptive immune system ?
- adaptive immunity consists of T cells and B cells
- T and B cells can recognise a huge range of proteins and molecules (called antigens) with a degree of specificity)
- Their specificity for the pathogen makes the immune response more effective
- Identifying and expanding the T and B cells that recognise the pathogen takes time, which is why adaptive immunity is slow
- T and B cells can remember previous encounters with pathogens (immune memory)
What are the 3 main types of T cells ?
- Helper T cells (Th cells); talks to other cells, co-ordinate immune responses, amplify innate immunity
- Regulatory T cells (Treg cell): Turn-off immune responses
- Cytotoxic T cells (CTL): kill infected cells
