Infection 6 - Adaptive Immunity (Part 1 - Recognition Phase) Flashcards
The two important cell types in the adaptive immune response are APC’s + T cells. What are the 4 APC’s and 2 T-cell cell types?
- APC’s = dendritic cells, langerhans cells, B-cells + macrophages
- T-cells = naive (never encountered the pathogen) + effector (have encountered the pathogen + capable of performing effector functions)
What is the role of APC’s?
What type of T-cells do the 4 APC’s present the pathogen to?
Present antigens from pathogens on MHC molecules on their surface to initiate adaptive immune response by taking antigen to lymphatic system for T-cell recognition.
- Dendritic + langerhans to Naive T-cells
- Macrophages + B-cells to Effector T-cells
What are the key features of APC’s?
1) Strategic locations - e.g.: mucosal membranes, skin, blood, lymph nodes + spleen.
2) Diversity in PRR’s - looking for different PAMP’s and can recognise extracellular pathogens (bacteria, fungi + protozoa) and intracellular pathogens (viruses)
3) Diversity in pathogen capture mechanisms - phagocytosis (whole microbes) + macropinocytosis (soluble particles)
Pathogens are presented by Major Histocompatibility Complex (MHC) molecules. What kind of cells express type 1 and type 2 MHC molecules?
What kind of microbial peptides do each class present?
1) Type l = antigen-presenting cells (dendritic cells, macrophages + B-cells) - present microbial peptides from intracellular pathogens (viruses)
2) Type ll = All nucleated cells (e.g.: macrophages) - present microbial peptides from extracellular pathogens (fungi, bacteria, parasites)
Describe the processing of intracellular microbes via the endogenous pathway (viruses)
- Intracellular microbes (viruses) are presented by APC’s on MHC class l molecules.
- APC’s express viral peptides on MHC class 1 after being marked for destruction by proteasome
- Presentation to naive CD8+ T-cells causes activation in lymphoid tissue, these search and kill infected cells as any infected cell will express viral peptides on MHC class 1 molecules
Describe the processing of extracellular microbes via the exogenous pathway (bacteria, fungi + protozoa)
- Extracellular microbes (bacteria, fungi + protozoa) are presented by APC’s on MHC class ll molecules
- Microbes captured by phagocytosis, peptide-rich vesicles fuse with vesicles containing MHC class ll molecules.
- APC’s present peptides of extracellular pathogens to CD4+ T-cells
Which molecules recognise MHC class l and class ll molecules?
Class l = recognised by CD8+ molecules on T-cells
Class ll = recognised by CD4+ molecules on T-cells
How do antigen presenting cells activate the right adaptive immune response?
- MHC molecules have a peptide binding cleft (for antigens) with a variable region with highly polymorphic residues.
- Therefore, many peptides can be presented by the same MHC molecules
- Everyone had different sets of MHC molecules therefore people have different susceptibilities to infections
What are the 2 major clinical problems associated with MHC molecules?
1) Major cause for organ transplant rejection - HLA (human leukocyte antigen) molecules mismatch between donor and recipient
2) HLA association with autoimmune disease - in ankylosing spondylitis + T1DM (insulin dependent diabetes mellitus)