Overview of the adaptive immune system Flashcards
What are the key points to the Adaptive Immune System?
→ Part of the immune system that has enhanced rapidity, potency or specificity as a consequence of previous events (exposure or vaccination)
→ Memory is the key element
→ “Anamnestic response” – not forgetting
Why have adaptive immune responses?
→ Protection from and defence against pathogens essentially
→ Also role in malignancy surveillance
→ Also linked to damage healing and repair
→ The same pathogens often come back and attack again- therefore gives an opportunity to have effectors ready which are specific and potent
→ Some pathogens stick around so they Need controlling
→ If every pathogen was completely “new” and every pathogen was completely eliminated after infection, there might be no need for an adaptive immune system
How can we spot a pathogen?
- Generic recognisable features – eg TLR – PAMP’s
- Recognition of a pathogen if there is tissue damage
The Danger Hypothesis – co-stimulation – CD28
Damage-associated molecular pattern molecules (DAMP) - these show up damage so allows pathogen to be recognised
→ Recognising pathogen that has been there before
→ Autoimmunity-self vs non-self
How can we describe/define lymphocytes?
Defining lymphocytes:
Morphology:
White cell; small, large nucleus
Lineage:
T and B cells
Location:
Tissue-resident memory cells (TRM)
Marginal zone B cells
Differentiation:
Naïve / memory (central, effector, stem cell memory)
Immature / mature or differentiated / senescent
Function: What they do
eg Helper / Cytotoxic / Regulatory / Antibody-producing
Phenotype: What surface markers they express
Eg CD4, CD8, CD28 … Usually functional receptors–
not just there for our convenience!
Specificity
What target – What Ab produced or epitope recognised (TCR)
Type of receptor
Ig class for B cells / αβ vs γδ for T cells
By what they produce
TH1 (IL-2, IFN-γ)
TH2 (IL-4, IL-5, IL-6, IL-10)
What are the two key features of the adaptive immune response?
Two key features:
1. Specificity
2. Memory
The pivotal role of clonal selection:
One clone – one specificity
Progeny can be expanded and retained
Clonal selection and adaptive immunity- what is the link/what do we know?
Basic tenet – one cell / one specificity
For B cells – one cell, one Ig
→ Defined by their antibody
→ May class switch / undergo affinity maturation
but always the same basic Ig
For T cells – one cell, one T cell receptor – TCR
→ Selection and expansion of that clone ± differentiation
→ Retention in “memory” of clonal progeny
Continued protection
Continued production of antibody (B cells / Plasma cells)
More rapid specific secondary responses (B and T cells)
What precursors do B and T cells emerge from?
Common lymphoid precursors
What does TCR (t cell receptor) do?
→ Detects a peptide sequence in association with MHC
→ Pathogen peptides need to be processed and presented
→ The T cell receptor recognises the peptide- it does not recognise proteins so the antigen presenting cell needs to cut up the protein into small pieces and present them to the MHC molecule.
→ All cells process their intracellular contents and present on MHC-I
→ Recognised by CD8 T cells through their TCR
Crucial to defence against viruses
→ Specialised antigen-presenting cells (APC) process and present peptides in MHC-II
binds to TCR on CD4 T cells
→ For this process to work, the T cell must bind the MHC well enough to recognise the protein.
→ Its a 2 step process in the thymus then after the cells come out the thymus,
→ Naïve cells recirculate primarily from blood to lymph nodes.
→ So cells for various diseases etc eg Ebola, flu etc are ‘sleeping’ waiting for an antigen to come by and ‘wake them up and then they would proliferate
What do activated B cells transform into?
→ Activated B cells transform into Plasma cells
“Antibody factories”
→ Also produce CD27+ memory B cells
