Adaptive Immunity Flashcards
What are the types of antigen-presenting cells?
Interdigitating dendritic cells - lymph nodes
Langheran’s cells - skin
Macrophages - various tissues
B cells - lymphoid tissues
Give features of antigen presenting cells
Placed in strategic locations eg mucous membranes, lymphoid organs and all lymphoid tissue
Pathogen capture to present pathogen
Diversity in pathogen recognition receptors
Which cells do antigen presenting cells present to?
T cells
When dendritic cells sense an extracellular microbe, what do they do?
Phagocytose it
Migrate to regional lymph nodes
Process the antigen
Mature into cells capable of activating naïve T cells
What is required to activate a naïve T cell?
Recognition of an antigen-MHC complex by the T cell’s TcR
Interaction of surface molecules on T cell antigen presenting cell
What are the surface molecules on T cells and antigen presenting cells which interact?
APC: CD80, CD86
T cells: CD28
Which cells are class 1 MHCs found and therefore which type of microbes do they present the antigens of?
All nucleated cells
Intracellular microbes eg viruses, bacteria, protozoa
Which type of T cell do class I MHCs activate?
CD8+
When an MHC class I activates a T cell, what happens?
CD8 is cytotoxic so kills the infected cell
Which cells are class II MHCs found on and so which type of microbial antigens do they present?
Dendritic cells, macrophages and B cells
Extracellular microbes such as bacteria, parasites, fungi, worms
What type of T cells do MHC class II activate?
CD4+ (T helper cells)
Once activated, what do CD4 cells do?
Activate B cells, natural killer cells, macrophages and other phagocytes to enhance the immune response
What do cytotoxic CD8 cells do?
Destroy infected cells with the same antigen as presented by the antigen presenting cells with MHC II
What do naïve B helper cells do?
Have antibodies which can recognise antigens of pathogens
Can then engulf and process the pathogen and present it on MHC II to the activated T helper cell
What happens when the naïve B cell has presented the antigen to the T helper cell?
The T helper cell activates the B cell so that is can differentiate into either a plasma cell or a memory cell
What do plasma cells do?
Produce soluble antibodies against the pathogen that triggers effector mechanisms to eliminate pathogens
What can memory cells do?
Have memory of the specific antigen and so can be removed quickly in the future
What can antibodies do?
Recognise specific antigens, then
- neutralise pathogens (prevent bacterial adhesion to healthy cells)
- opsonise pathogens (promote phagocytosis by coating the antigen)
- activate complement (allows opsonisation and induce cell lysis of the pathogen
What is the endogenous processing pathway of antigens?
Host cell digests cytoplasmic proteins of the intracellular pathogen by a specialised enzyme complex - cuts it into small peptides
Transporter associated with antigen processing (TAP) moves the peptide into the ER
Here it is coupled to an MHC I and transported to the cell surface
Explain the exogenous processing pathway of antigens
After maturation in lymph nodes, lysosome-associtaed enzymes digest the pathogen to produce smaller peptides
Dendritic fell displays the antigenic peptides on its surface, completing them to MHC II molecules
Complex recognised by at cells passing through the lymph nodes and CD4+ cells activated
What is a cytokine?
Any of various small regulatory proteins that regulate the cells of the immune system
What are antibodies/immunoglobulins produced by?
B lymphocytes - they are membrane bound
Plasma cells - produce soluble ones
What does the constant region of the antibody do?
Determines the type of antibody (IgE, IgA etc.)
What gives the variable region uniqueness?
Different amino acid sequences
What are the sites called within the antigen that the antibody recognises?
Epitopes
Features of MHCs?
Co-dominant expression - both parental gene types are expressed to increase the number of MHC molecules
Polymorphic genes - different alleles among different individuals increased the presentation of different antigens/microbes
Features of IgG?
Only antibody to be transferred across the placenta so protects baby for a short time after birth
The most abundant antibody
Can opsonise antigens for phagocytosis
Activates complement
Takes part in antigen-dependent cytotoxicity processes with NK cells and macrophages
Features of IgA?
Distributed in serum, nasal discharge, saliva, breast milk, bowel fluid
Protects GI tract of newborns via mother’s breast milk
Mostly involved in mucosal defences
Prevents adhesion to gut wall and neutralises viruses
Features of IgD?
Present on surface of B cells
Role in induction of antibody production
Features of IgE?
Involved in immunity against parasites
Allergic reactions
