S3 L2 - Adaptive immunity part 1 Flashcards
- *Role of Antigen-presenting cells**
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How do APC present the microorganism?
Types of APC cells?
- *Role of Antigen-presenting cells**
- Sense the pathogen
- Capture the pathogen
- Process the pathogen
- Present the pathogen
How do APC present the microorganism?
presents the pathogen via MHC molecules (on the suface on APC e.g. macrophages)
Types of APC cells?
pic
Features of Antigen-Presenting cells (APC)
• Strategic location
o Mucosal membranes (gut, lung)
o Skin (i.e., Langerhans cells)
o Blood (i.e., plasmacytoid cells)
o Lymph nodes (i.e., follicular dendritic cells)
o Spleen
• Diversity in pathogen sensors (PRRs)
o Extracellular pathogens (bacteria, fungi, protozoa)
o Intracellular pathogens (viruses)
• Diversity in pathogen capture mechanisms
o Phagocytosis (whole microbe)
o Macropinocytosis (soluble particles)
Major Histocompatibility Complex (MHC) molecules
- How is antigen presented on the Antigen Presenting cell e.g. macrophage?
- Two types of MHCs
- *How is antigen presented on the Antigen Presenting cell e.g. macrophage?**
- An antigen presenting cell, e.g. macrophage, will phagocytose a foreign pathogen, as part of the innate immune response.
- After taking in the pathogen and degrading it with lysozymes, a small sample of the antigen from the pathogen is then displayed (presented) on the surface of the macrophage using a molecule called MHC (Major Histocompatibility Complex)
- — the pathogen has been captured (phaocytosis), processed (digestion down to antigen fragments) and presentation (using MHC) —-
- *Two types of MHCs**
- MHC class 1
- MHC class 2
- *MHC Class I**
- Expressed on which cells?
- Presented after which response?
- Which pathogen?
- Which cell do they present to?
- *MHC Class 2**
- Expressed on which cells?
- Presented after which response?
- Which pathogen?
- Which cell do they present to?
Recap:
Viruses - which pathway, presented by which class?
Bacteria, fungi and parasites - which pathway, presented by which class?
MHC Class I
- Expressed on which cells?
All nucleated cells
- Which response?
Intracellular pathway
- Which pathogen?
Viruses
- Which cell do they present to?
CD8+ receptors
1 x 8 = 8
MHC Class 2
- Expressed on which cells?
Expressed on antigen-presenting cells dendritic cells, macrophages, B cells
- Which response?
Extracellular pathway
- Which pathogen?
Bacteria, Fungi, Parasites, Virus
- Which cell do they present to?
CD4+ receptors
2 x 4 = 8
Recap
pic
- *Endogenous pathway** - Processing of intracellular microbes
- How is the pathogen processed to then presented
- *Processing of intracellular microbes - Endogenous pathway (2nd flashcard)**
- How does the interaction between APC with MHC class 1, non-APC cells with MHC class 1 and CD8+ T cells
- *Endogenous pathway**
- What is the pathogen presented to? (recap)
- What happens next (next stage)
- What is the pathogen presented to?
Presented by MHC Class I to CD8+ T cells.
CD8+ T cells are Tc cells
- What happens next (next stage)
Cell-mediated immunity
Tc cells are killer cells, kill any infected body cell
- *Exogenous pathway - Processing of extracellular microbes**
- How is the pathogen processed to then be presented
- *Exogenous pathway**
- What is the pathogen presented to? (recap)
- What happens next (next stage)
- What is the pathogen presented to? (recap)
MHC Class II molecule presents these antigens
Presents them to CD4+ T cells (these are TH cells) - What happens next (next stage)
TH cells differentiate into either Th2 or Th17
– Th17: activates IL17. IL17 activates neutrophils
– Th2: activates interleukins that cause:
Eosinophil increase in number
B cells to produce antibodies
Mast cells that are responsible for inflammation and allergic reactions
Key features of MHC Class I and Class II
• Co-dominant expression: o Both MHC class I and II parental molecules are co-expressed in each individual (6 of each class)
• Polymorphic genes (different alleles):
o Different individuals present and respond to different microbes
• Broad specificity: Many peptides are presented by the same MHC
Clinical importance of MHC molecules
• No two individuals have the same set of MHC molecules
- Ensures that humans won’t be wiped out by a single microbe/epidemic disease
• Different susceptibilities to infections - Strong vs weak immune response against infectious microbes
- Depends on the MHC molecules the individual has (polymorphism)
- their immune status (i.e. immuno compromised?)
Clinical problems with MHC molecules
• Major causes for organ transplant rejection
o HLA molecules mismatch between donor and recipient (Allograft) o Graft-Versus-Host reaction (GVH)
• HLA association with autoimmune disease e.g. Diabetes Mellutis
