Exam 2: Dr. Pharr Immunity Mediated by B-cells and Antibodies Flashcards
What happens in the first week of the primary immune response?
- Recognition of antigen
- Activation by helper T cells. Formation of a primary focus
- Differentiation to short-lived plasma cells
What is a primary focus?
A pool of B cells resulting from the proliferation of antigen activated B cells over the course of about 3-4 days
What do short-lived plasma cells produce?
IgM to clear the infection
In the second week of the primary immune response, what steps are taken to protect against future infections with the same pathogen?
Development of antibodies with a new heavy chain isotype and with a higher affinity for epitopes derived from the original pathogen
Development of memory B-cells and long lived plasma cells
How many days are there before an immune response can be seen for the first time? Second time?
7-10
3-5
what is the outcome of signal one in the first week of the primary immune response?
Prepares B cells for collaboration with effector helper T cells
What is formed in the second week of a primary immune response?
Germinal centers
What is a germinal center?
A site of B cell proliferation in the B cell area of secondary lymphoid tissues
What are the functions of germinal centers?
Isotype switching
Somatic hypermutation
Differentiation into either antibody-secreting long-lived plasma cells or memory B cells
What does isotype switching allow for?
Efficient elimination of the pathogen
What happens in the process of somatic hypermutation?
Point mutations are generated in the variable region of the heavy chain and light chain genes
B cells in the germinal center are then elected for high affinity recognition of the original antigen epitope
What does somatic hypermutation allow for?
Efficient recognition of the pathogen
What does germinal center differentiation into either antibody-secreting long-lived plasma cells or memory B cells allow for?
Protection from reinfection and disease
What will long-lived plasma cells do?
Migrate to the bone marrow and secrete the higher affinity and isotype switched antibody that is observed during the later part of the immune response
What will memory B cells do?
Maintain surveillance of secondary lymphoid tissues
What characteristics of the antibody response will be helpful in preventing disease from the same pathogen?
- The antibody response occurs more rapidly
- Antibody levels will be higher than the level attained with the primary response
- The antibodies produced will have a higher affinity for the antigen epitope
- The antibody will consist of an isotype different from IgM
What are the 2 types of antigens encountered by B cells?
Thymus-dependent protein antigens
Thymus-independent non-protein antigens
What do thymus-dependent protein antigens require?
T cell help for B cell proliferation and differentiation
What can the repeated epitopes of thymus-independent antigens do?
Engage a number of B cell receptors
What is the multitude of signals with the thymus-independent antigen sufficient to do?
Induce B cell proliferation and differentiation to short lived plasm cells secreting IgM
This results in an early IgM response to an infection
Describe mature naive B cells
Diverse repertoire of antibody specificities–respond to thymus-dependent antigens
Require T cell help for activation
Located in secondary lymphoid tissues
Recirculate between the blood and lymphatics
Describe marginal zone B cells
Respond to pathogens in the blood
Differentiate to short-lived plasma cells secreting IgM
Located in the marginal zone of the spleen where blood is filtered
Describe B1 B cells
Respond to pathogens entering the major body cavities
Differentiate into short lived plasma secreting IgM
Located in the peritoneal and pleural cavities
What does IgM do?
Protects the bloodstream
What does IgG do?
Protects the bloodstream, extracellular spaces in tissues, and lymphatics
Describe IgA: Where is it? What does it do?
First line of defense
Present in mucous secretions
Protects epithelial surfaces
What does IgE do?
Second line of defense behind IgA
Stimulates an inflammatory response
What does IgD do?
Participates as a BCR on naive B cells
In what general ways do antibodies clear infections with extracellular pathogens and their products?
Focus defense mechanisms onto the pathogen itself–the antibody links that pathogen with the leukocytes and plasma proteins that will eliminate it
What do phagocytes express?
Fc receptors for antibody bound to a pathogen
Complement for C3b bound to a pathogen
When is the effector function of IgM produced?
In the primary response to an infection
Is IgM recognized by Fc receptors of phagocytes?
No
How does IgM clear an infection?
It is a very potent activator of complement
It is specialized to activate complement efficiently upon binding to the pathogen
What is C1q?
The first component of the classical pathway of complement activation
What must C1q do to become activated?
Bind to 2 or more antibody heavy chains, which requires multiple molecules of IgG bound to the pathogen
What are the main effector functions of IgG?
Neutralization*
Opsonization*
Antibody-dependent cell-mediated cytotoxicity (ADCC)
What is neutralization?
Antibodies can prevent infection by coating the surface of a pathogen and therefore prevent the pathogen from binding to healthy cells
What is an opsonin?
A substance that enhances phagocytosis
What is involved with opsonization?
Macrophages and neutrophils
What is involved with ADCC?
NK cells
What do NK cells do in ADCC?
They use their Fc receptors to bind to antibody-coated cells, which they kill by inducing apoptosis
What are the antibody coated cell recognized by NK cells?
Virus infected cells
Tumor cells
When is the IgA isotype formed?
After a primary response to a pathogen that invaded the body through the internal epithelial linings
What secretes IgA?
Long lived plasma cells
How does IgA provide the first line of defense against reinfections?
IgA is present in mucus secretions that cover the internal epithelial lining of the body
How does IgA protect the epithelial surfaces?
Neutralization
Does the IgA dimer activate complement?
No
What does the primary response to parasite and some bacteria result in?
Long lived plasma cells secreting IgE
What is IgE important in?
Reinfections with parasites that invade the internal epithelium
What does IgE provide mast cells?
The ability to sense pathogens
Where are mast cells located?
Beneath the epithelial surfaces of the skin, respiratory tract, and gastrointestinal tract
What do mast cells express?
Fc receptors for IgE
What happens when an antigen binds IgE on the surface of mast cells?
The release of histamine stimulates an inflammatory response
How does IgE provide a second line of defense agains reinfection with pathogens that invade the intestinal epithelium and enter the underlying tissue?
IgE is bound to the surface of mast cells and is responsible for mast cell activation in response to pathogen invasion
What do eosinophils express?
Fc receptors for IgE
