L1 - An overview of immunology Flashcards
What is an antigen
- Anything the immune system to responds do
- Usually protein
- Not necessarily ‘bad’
Function of an antigen receptor
- Recognises the antigen
- Fundamental basis of immunity
- Basis of division into innate and adaptive
What is an effector mechanism
- An action to respond to the antigen
Type of stem cells produced by the bone marrow
- Pluripotent hematopoietic stem cells
What can the pluripotent hematopoietic stem cell differentiate into
- Common lymphoid progenitor
- Common myeloid progenitor
What can the common lymphoid progenitor cell differentiate into
- B cell
- T cell
- NK cell
What can a common myeloid progenitor cell differentiate into
- Granulocyte/macrophage progenitor
- Megakaryocyte/erythrocyte progenitor
What can a granulocyte/microphage progenitor cell differentiate into
- Neutrophil
- Eosinophil
- Basophil
- Unknown precursor of mast cell
- Monocyte
What do megakaryocytes differentiate into
- Platelets
What do erythroblasts differentiate into
- Erythrocytes
What do monocytes differentiate into
- Macrophages
What cells can differentiate to form immature dendritic cells
- Hematopoietic bone marrow progenitor cells
Function of neutrophils
- Phagocytosis
Function of eosinophils
- Helminth infections??
Function of monocytes(circulating macrophage tissue)
- Phagocytosis
- Antigen presentation
Function of dendritic cells
- Antigen presentation
Function of basophils (tissue-resident counterpart = mast cell)
- Helminth infections
Features of lymphoid lineage
- Similar size to RBC
- Little cytoplasm with few granules
Functions of B cells
- Make antibody, antigen presentation
Functions of T cells
CD4 - Help other components of immunity
CD8 - Kill infected cells
Type of immunity provided by T cells and B cells
- Adaptive immunity
Features of NK cells
- Actually innate lymphocytes
- Direct lysis of infected cells and antibody-dependent cellular cytotoxicity
Types of intercellular signalling
- Endocrine
- Paracrine
- Autocrine
- Juxtacrine
What are cytokines
- Cytokines are small proteins released by cells that have an effect on another cell
Why are cytokines important
- They are important for communication between cells of the immune system and between immune system cells and other cells and tissues
Cytokines vs Chemokines
Chemokines are similarly defined, but
- Different structure, receptors and nomenclature
- Main role is temporal and spatial organisation of cells and tissues
Key features of innate antigen receptors
Do not recognise antigen specifically
- Pattern recognition receptors’ (PRRs)
- Recognise ‘pathogen associated molecular patterns’ (PAMPS)
- Genome-encoded
- Not clonally distributed
What do manose binding ligands bind to?
- MBL binds with high affinity to mannose and fucose residues with correct spacing
- Mannose and fucose residues that have different spacing are not bound by MBL
Classical features of innate immune receptors/defences
Work quickly - first line of defence
Adaptive immunity takes more time to be activated
Unable to ‘learn’, as germline encoded and therefore cannot change - therefore no memory
Key features of adaptive antigen receptors
- Recognise antigen specifically
- T cell receptor, B cell receptor (antibody)
- Huge receptor diversity
- Clonally distributed
- Permit specificity and memory in immunity
How are adaptive antigen receptors produced
- Produced by random somatic recombination events between gene segments
Features of B cell receptors
- May be surface-bound or secreted
- Recognises intact antigen
Features of T cell receptors
- T cell receptor is very similar to the B cell receptor
- Only a surface receptor on CD4 and CD8 T cells
- Recognises processed antigen in the form of linear peptides
How do somatic recombination events occur
- T and B cell receptors are produced by random recombination events between V, (D) and J gene segments, producing a huge receptor diversity despite a small number of genes
- The most useful receptors are selected after birth upon exposure to pathogens
What happens to clonally-expanded T and B lymphocytes after primary infection
- After primary infection, most clonally-expanded T and B lymphocytes die off; a few remain as long-lived memory cells
Examples of effector mechanisms
- Barriers (skin, acid pH in gut etc)
- Cytokines
- Complement
- Phagocytosis(enhanced by opsonisation)
- Cytotoxicity (CD8 T cell, NK cell)
- Antibody-dependent cellular cytotoxicity
- Mast cell and eosinophil degranulation
Are effector mechanisms specific to types of immunity
- Effector mechanisms are shared between innate and adaptive immunity
- Adaptive immunity is defined by its receptors, not by its effector mechanisms
How do CD8 T cells function
Antigens inside a cell are bound to class I MHC molecules, and brought to the surface of the cell by the class I MHC molecule, where they can be recognized by the T cell.
If the TCR is specific for that antigen, it binds to the complex of the class I MHC molecule and the antigen, and the T cell destroys the cell.
In order for the TCR to bind to the class I MHC molecule, the former must be accompanied by a glycoprotein called CD8, which binds to the constant portion of the class I MHC molecule.
Therefore, these T cells are called CD8+ T cells
Features of acute inflammation
- Hot
- Painful
- Red
- Swollen
Blood vessel changes that underlie the process of acute inflammation
- Vasodilatation
- Adhesion molecules
- Increased permeability
- The clinical features are therefore defined by an interaction between the pathogen and host immunity
