Antibodies, B-cells Flashcards
What are the 2 B-cell sub populations?
- Innate like B-cells which produces antibodies
- Follicular B-cell, which develops a memory and responds to protein antigens
In the antibody there 2 regions, name them and say what they bind to.
- Variable region which binds to an antigen
- constant region which binds to Fc-receptors
Name some of the effector functions of the antibody
(It’s okay if I know like 4)
- neutralize microbe and toxins
- opsonization and phagocytosis
- antibody dependent cellular toxicity
- phagocytosis of microbes opsonized with complement fragments
- inflammation
- lysis of microbes
What are the first antibodies to be expressed in a B-cell?
IgM and IgD
What does IgM do?
Important in early defense against pathogens and in maintaining homeostasis.
- activating the complement system
- opsonin
What does IgD do?
It is one the antibodies that are first expressed in a B-cell
What does IgE do?
- It’s associated with allergic reactions
- Associated with parasitic responses
- Induces histamine release by cross-linking Fc-epsilon receptors on mast cells
What does IgA do?
- It keeps immune attacks against the
bacterial flora in the gut under control - dominant in intestine
What does IgG do?
- Dominant antibody in the circulation
- complement activator
- Effective opsonin for phagocytosis of microbes
What contributes to antibody diversity?
- Heavy and light chains combine into an antigen-binding cleft
- VDJ recombination; Each chain is encoded by several gene sequences that are randomly assembled into one gene
- Addition or removal of nucleotides in VDJ recombination
Name all the development stages (without detail) of a B cell (It can become an antibody-producing plasma cell or a memory B-cell)
- Development and maturation in the bone marrow
- Selection in the bone marrow
- Antigen interaction and activation
- Somatic hypermutation
- Isotype switch
Describe the development stage of a B-cell in the bone marrow (3 steps)
- The pre-b-cell will express one chain of the antigen receptor. If it’s not expressed => cell death
- The pre-b-cell will express complete antigen receptor. If it’s not expressed => cell death
- If the receptor recognizes an antigen then it will lead to cell death or be sent for receptor editing. If not its a positive selection it’s now a mature B-cell
After the B-cell matures it migrates to secondary lymphoid organs and follow the chemoattractants CXCL13 to B-zone. How does the B-cell activate (3 parts)?
- An immature DC captures an antigen, matures and travels via lymphatics to the lymph node. It then presents the antigen to a naive T-cell to activate it
- The same antigen is encountered by a B-cell in the follicle. The B-cell takes in the microbial antigen and breaks it down to peptides => MHC-II peptide complex
- Activated T- and B-cells migrate towards each other with the help of chemoattractants. The B-cell presents the antigen to the Th-cell along with some co-stimulation => activated B-cell
The activated B-cells then migrate back into the follicle and make clones of themselves. Describe what isotype switch implies in B-cells
B-cells can switch antibody isotype via cytokines and with the help of T-cells. They can switch depending on what type of problem the immune system needs to resolve (aka which cytokines are released).
- IgM => complement activation
- IgG => complement activation and Fcr dependent phagocyte responses
- IgE => immunity against parasitic worms and mast cell degranulation
- IgA => mucosal immunity
What happens in somatic hypermutation?
It contributes additional mutations to the light chain mediated by the enzyme AID. It creates a high affinity antibody which reacts faster to phagosome.
