Immunity Flashcards
What is the definition of an infectious disease?
When a pathogen succeeds in evading/overwhelming the host’s immune system
What is the definition of the immune system?
Cells/organs that contribute to immune defences against infections & non-infectious conditions
- pathogen recognition
- contain/eliminate infection
- resolution
- memory
What are the key differences between the innate and adaptive immune systems?
INNATE ADAPTIVE
Fast (seconds) Slow (days)
Non-specific (groups of microbes) Specific (one pathogen)
No memory Memory
No change in intensity Increases in intensity
What factors of the innate immune system limit the entry and growth of pathogens?
PHYSICAL: skin, mucous membranes, bronchial cilia
PHYSIOLOGICAL: diarrhoea, vomiting, coughing, sneezing
CHEMICAL:
- low pH (skin, stomach, vagina)
- antimicrobials (gastric acid & pepsin, mucus, IgA in tears & saliva, lysozymes in sebum & urine & sweat, beta-defensins in epithelium)
BIOLOGICAL: external commensals compete with pathogens for attachment sites/resources, produce antimicrobials, synthesise vitamins
How do the components of adaptive immunity lead to an immune response?
Naive T-cell (not been exposed to antigen/pathogen) + Antigen-presenting cell + Pathogen = Immune response
What are the important features of antigen-presenting cells?
Antigen-presenting cells = B-cells, interdigitating dendritic cells (lymph nodes), Langerhan’s cells (skin), macrophages
Location:
- skin (skin-associated lymphoid tissue)
- mucous membranes (& associated lymphoid tissue)
- lymphoid organs (lymph nodes + spleen)
- blood circulation (plasmacytoid + myeloid dendritic cells)
Macrophages can phagocytose whole microbes, whilst other antigen-presenting cells use micropinocytosis (random uptake of soluble microbe)
Cell-surface receptors sense extracellular microbes (bacteria), intracellular receptors sense intracellular microbes (viruses)
How are naive T-cells alerted to the presence of a pathogen?
Major Histocompatibility Complex (MHC)/Human Leucocyte Antigen (HLA) (on cell membrane)
MHC Class 1:
- found on all nucleated cells (any cell which can be infected by viruses)
- present peptides from intracellular microbes (endogenous pathway) to CD8+ T-cells
- CD8+ T-cells bind at the alpha-3 subunit
MHC Class II:
- found on dendritic cells, macrophages, B-cells (+ some activated T-cells, in thymus, in intestine)
- present peptides from extracellular microbes (exogenous pathway) to CD4 +
- CD4+ T-cells bind at the beta-2 subunit
note: genes involved in MHCs are co-dominant (increased no. of different types of MHC that are present) and are polymorphic (more antigens/microbes are able to be presented)
What are some problems caused by MHC molecules?
Organ transplant rejection (mismatch between HLA variants present in the donor and the recipient) -> recipient immune system attacks donor tissue
Graft v.s. host -> donor immune system attacks recipient tissue
Association with autoimmune diseases e.g. ankylosing spondylitis, insulin-dependent diabetes
Contrast the general immune response to extracellular and intracellular microbes.
Extracellular microbes —> endogenous pathway —> MHC II —> binds CD4+ T-cells —> humoral immunity (non-cell mediated: antibody & complement)
Intracellular microbes —> endogenous & exogenous pathways
- > endogenous —> MHC II —> binds CD4+ T-cells —> cell-mediated immunity (antibody, complement, macrophages)
- > exogenous —> MHC I —> binds CD8+ T-cells —> cytotoxic T-cells
Contrast the actions of B-cells and macrophages.
B-cells:
- antibody-dependent cell cytotoxicity (IgG, IgE)
- opsonisation (IgG)
- neutralisation (IgA)
- complement activation
- allergies (IgE)
Macrophage: phagocytose opsonised microbes
Where are macrophages located?
Liver
Gut
Lungs
Spleen
What is MALT?
Mucosal associated lymphoid tissue
- GALT (gut associated lymphoid tissue) = Peyer’s patches, appendiceal lymph nodes, tonsils
- thyroid
- breast
- lung
- salivary glands
- skin
Contains lymphocytes, macrophages, plasma cells (+ M cells in intestinal MALT which sample antigens)
Explain the location of the tonsils.
Pharyngeal (adenoid) tonsils
Palatine tonsils
Lingual tonsils
Drain into cervical lymph nodes which lie along the jugular vein
e.g. adenovirus often causes sore throats and cervical lymphadenopathy
Where are the Peyer’s patches? What conditions can cause inflammation of the Peyer’s patches?
Found in the ileum (differentiates the ileum from the duodenum - contains Brunner’s glands - and the jejunum - no Peyer’s patches or Brunner’s glands)
Ileocaecal lymphatic tissue important as the large intestine has a large no. of microbes
Typhoid fever causes inflammation of Peyer’s patches in the terminal ileum (can cause perforation)
Mesenteric adenitis (inflammation of mesenteric lymph nodes e.g. adenovirus/Coxsackie virus) —> right iliac fossa pain
What is the immunoglobulin responsible for passive immune protection of neonates via breastfeeding in the mucosal membranes (respiratory and GI)?
IgA
