Development of Lymphocytes Flashcards
(42 cards)
What are the cells in the innate immune system?
- Neutrophils
- Monocytes
- NK cells
- Basophils
- Eosinophils
- Macrophages
- Tissue cells and endothelial cells (not immune cells necessarily)
- Platelets (not immune cells necessarily)
What are the cells in the adaptive immune system?
- B cells
- T cells
- Plasma cells
What may happen when a person doesn’t have lymphocytes?
- Paraesthesia in the head and arm (numbness and tingling/0
- MRI shows area of oedema caused inflammation
- Ring enhancing vascular permeability
- Ring of inflammation, with ring of swelling
- Infection of the brain
- Likely have a toxoplasma infection
- Low CD4 count has allowed an opportunistic infection to get through the immune defences
- Patient is given anti-viral treatment for toxoplasmosis and is doing well
Which cells do primary/secondary lymphocyte deficiency affect?
B cells or T cells
What are the lymphocyte deficiencies that can occur in B cells?
- Congenital agammaglobulinemia: lose the Ig
- Common variable immunodeficiency
- May be due to side effects of certain drugs such as Rituximab
What are the lymphocyte deficiencies that can occur in T cells?
- Severe combined immunodeficiency (SCID)
- DiGeorge syndrome
- Acquired HIV, chemotherapy/novel biologics
Define a lymphocyte
A white blood cell part of the adaptive immune response either a T cell or B cell.
What is the morphology of a lymphocyte?
Small cell with a large nucleus
What is the functions of lymphocytes?
- A helper cell
- A cytotoxic cell
- A regulatory cell
- Etc
What are the specifities of a lymphocyte?
It has specificity which can be which type of antibody it produces or, what epitope it recognises via the TCR which can be different. It can produce different cytokines
What are the two key features of adaptive immunity?
Specificity and memory
What is the specificity of B cells?
- One cell will produce one Ig.
- The Ig may have class switch (go from IgM to IgG), but it will always be the same basic Ig.
- It may undergo affinity maturation.
What is the specificity of T cells?
- One cell will have one TCR receptor and recognise one antigen.
- There will selection and expansion of that clone
- This will lead to retention in memory of the clonal progeny
- Leads to continued production of antibodies and a more rapid specific response.
How is specificity of the adaptive lymphocyte achieved?
This is done due to the hypervariable region on the TCR, meaning there is diversity between the binding region of each T cell and therefore more specific to the antigen.
How does the immune system predict the infection?
- Whether it looks like a foreign body: pathogens display generic recognisable features (PAMPs and TLRs) which allow the immune system to recognise them as foreign etc
- If the presence is associated with damage: the danger hypothesis meaning whether the pathogen will lead to tissue damage producing DAMPs which the immune system will be able to recognise.
- Previous exposure to pathogen: memory cells against previous infection.
- Recognising non-self: attacking accordingly based on what is self and non-self. If this goes wrong, it leads to autoimmune diseases.
How does the immune system predict pathogens that are unknown?
Through the huge diversity between TCRs and BCRs; this means that by chance one of them should be complementary to the antigen. However, this might have some issues.
What are the issues with the immune system trying to predict unknown pathogens?
- The response will be delayed, this is why the primary response is slow.
- Might miss some pathogens if the TCR/BCR is not complementary
- May lead to self-recognition as enemy
How does the immune system recognise cancer cells?
It is harder for the immune system to detect because cancer cells are still self-cells.
- Cancer cells express cell signals such as MHC.
- The immune system is able to recognise these signals and express signals but only specific to cancer cells.
Describe the binding of TCR-MHC peptide binding
- MHC I molecule binds to the antigen peptide via its groove.
- It expresses it on the surface for CD8 T cells. Every cell will express MHC I.
- MHC II molecule binds to the antigen peptide via it’s groove and expresses it on the surface for CD4 T cell.s
How is thymic selection carried out?
This is done via positive selection and negative selection in the thymus. T-cells are trained to recognise antigens and not self-cells, they need to be active but not overreactive or underactive.
What is positive selection of B cells?
- This is the ability of the T cell to bind to MHC molecules.
- Therefore, during positive selection, the T cells are checked for their ability to bind to MHC molecules.
- If they can’t they are neglected and killed.
What is negative selection of T cells?
- Once the cells pass positive selection, they undergo negative selection.
- This is the ability of the T cell not to bind to self-peptides.
- Cells in the thymic medulla express specific tissue antigen such as oesophageal.
- For the T cells to pass negative selection, they need to NOT bind to those antigens.
- If they bind, they are neglected and killed.
- Once all this process is passed an array of naive T cells is set up because they haven’t met antigens yet.
What happens in the B cell repertoire selection process?
Positive selection, receptor editing and negative selection
What is the positive selection of B-cells?
B cells don’t recognise MHC because it is not their job.
- Positive selection is used to identify the B cells which have completed their antigen receptor gene rearrangment successfully.
- This means that only B cells which express functional membrane Ig molecule (BCR) receive constitutive BCR derived signals.
- These signals are required to keep the immature B cells alive.
