Humoral specific immunity Flashcards
What are antibodies?
They start as B cell membrane bound (BCR) before being secreted as their own molecule. AKA immunoglobulins (Ig). Bind to antigens to elicit the immune response through opsonization and neutralisation.
What is the structure of antibodies?
Y shape.
The normal Y shape is all the heavy chain, but underneath the either side of the arms of the Y, there is another small chain termed the light chain. The constant region of the Ig is the leg and start of the arms, and the variable region is the end of each arm, on both heavy and light chains. On the end of the variable regions, we have hypervariable regions which are what are specific to the antibody.
The hinge regions are linked by disulphide bridges.
The top of the Ig is the N terminus, the bottom is the C terminus.
What is the Fab and Fc region of an Ig?
FAB = fragment antigen binding meaning the antigen-binding region (arms of the Y).
FC = fragment crystallizable is the leg of the Y. It binds to effector cells (immune cells) to signal a response to the pathogen bound to the antigen binding site.
What are the two main functions of antibodies?
Bind - specifically to epitopes on the pathogen/ Ag surface to elicit the immune response (neutralisation and opsonisation).
recruit - cells and molecules to destroy the pathogen/ Ag. The region involved with effector function is the constant (Fc).
What is an epitope?
Part of the antigen in which the Ig binds itself to - specific binding regions.
What are the functions of antibody binding?
- neutralise
- agglutinate
- opsonize (VA L20)
- activate complement
What are the functions of antibody recruitment?
- improve phagocytosis
- ADCC
- degranulation
What is the process of neutralising?
The Ig binds to the bacteria surface and prevents its interaction with cell receptors in the host. this prevents pathogen uptake by target cells and allows them to be uptaken (as a whole Ag:Ig unit) by macrophages during phagocytosis.
What is agglutination?
Ig variable regions will bind to the epitopes on Ags and try to bind closely together with other binding antibodies. This causes them to all clump up and lots of the antigen particle will now be all in one space. It creates a bigger target for the immune system for more efficient recruitment.
What is opsonization and what are the types?
The antibody will bind to the antigen and completely coat it, marking it for destruction.
Extracellular proteins binding to mark the pathogen for destruction via phagocytosis.
Direct = binding of the Ig constant region (Fc) receptors to phagocyte receptors
Indirect = increases complement C3b deposition on a pathogen and binding to the complement receptors (CR1).
How does antibody binding initiate the complement?
Activates the classical pathway.
Ag-Ig complex binds C1 and then acts on C4 and C2 to generate C3 convertase which will eventually activate the membrane attack complex (MAC) to lyse the pathogen.
How does the antibody recruit the ADCC?
ADCC = antibody dependant cellular cytotoxicity
This is the detection of antibodies by FcR on several cell types that induces activation (degranulation).
It lyses target cells and involves NK cells.
The point of ADCC is to induce cytolytic action of immune cells.
What is degranulation?
degranulation of mast cells (allergies and parasites) by Nk cells and eosinophils (ADCC).
Mast cells contain histamine, upon activation will release it and degranulate negative cells. Histamine is potent and therefore only activated in a small amount and mast cells must be regulated. they are regulated by the fact several antibodies need to be bound to release histamine. Eosinophils attack schistosome larva in the presence of antibodies.
How do you culture antibodies?
By fusing an individual B cell making an antibody of interest with a B cell tumour line which grows indefinitely in culture, we can generate hybridoma which gives us an unlimited supply of monoclonal antibody (mAb).
What is an enzyme linked immunosorbent assay (ELISA)?
They utilise the specificity of the antibodies - if nothing is specific to the antigen then nothing will bind.
