Acquired immunity B cells and antibodies Flashcards
What type of cells secrete antibodies?
Only B cells or immunoglobulins
antibody function
- bind to extracellular bacteria and viral particles and inactivate/prevent adherence/infection
- antigen-antibody complex is recognized by macrophages
- bind to toxins and neutralize them
- toxin-antitoxin antibody complex cannot bind to target cell
- can activate complement system
- bind to aged/damaged cells so they can be phagocytosed
coating of antigen by antibody is a type of opsonization
pathological role of antibodies
- antibodies against self antigens (autoantibodies) destroy self tissue = autoimmune disease
- antibodies provoke exaggerated/inappropriate response= allergies
- B cells become tumorgenic, cancer = myeloma
myeloma
- plasma cell tumor
- arise from single precursor cell (starts in bone marrow)
- secrete single Ig of any class called myeloma protein (antibodies)
- way too much of one antibody is produced
- causes immune suppression becuase B cells cant react to other antigens
autoimmune hemolytic anemia
autoantibodies against RBCs
RBCs are destroyed= jaundice
Lupus
antibodies against skin and joints
arthritis, rashes
Rheumatoid arthritis
antibodies against synovial membrane and joint tissue
arthritis
Type I sensitivity
allergic response
IgE and eosinophils
for IgE antibody generation, Th2 and IL-4 is essential
B cell development
- stem cell in bone marrow
- pre B cell in marrow with cytoplasmic u chains
- immature B cell in marrow with membrane bound IgM, IgD
- mature B cell in marrow, lymph node, spleen with antibodies
- differentiation into plasma (Ig secretion) or memory cell
primary lymphoid organs
development occurs
no antigen interaction
Bone marrow (B cells, primary and secondary), thymus (T cells), peyers patches
B cell functions
- secrete Antibody (or immunoglobulin) production
- Antigen processing and presentation
only effective against extracellular pathogens, antibodies cannot enter cells
2 forms of antibodies:
- Secretory: Detected in the fluids such as serum, peritoneal cavity, mucosal fluids (“humors”) etc.
* They neutralize antigen and assist in their removal. - membrane bound: Important for specific binding to antigens
* B cell receptor (BCR) 200,000 to
500,000 identical antigen receptors (T cells have around 30,000 TCRs), Each BCR is specific to only ONE antigenic epitope.
- Antibodies recognize Free Antigens (i.e. do not require
combination with MHC unlike T cells) - Antibodies are Specific: Bind specifically to the antigen, which
induced antibody production - Cannot Penetrate the cell!
antibody structure
- They are glycoproteins made of 4 polypeptide chains.
- Have a flexible Y shaped structure
- amino end: where antigen binds, has variable V region
- carboxy end: bind to membrane
- 2 heavy and 2 light chains
- hinge region
antibodies recognize SHAPE/SEQUENCE of antigen
antibodies recognize SHAPE of antigen
primary vs secondary immune response antibody differences
primary: short peak, IgM
secondary: tall peak, other antibodies
Th1/Th2 and class switching
Th1 and Th2 cytokines trigger the switching of IgM to IgE/IgA/IgD/IgG
B cell receptor (BCR) recombination
BCR determines specificity of B cells
(ex: BCR for salmonella antigen is different than BCR binding e. coli)
recombination of genes for BCR leads to variable region of BCR
Th2 cytokines acting on B cells
Th2 cells secrete cytokines that initiate B cell activation and differentiation.
* IL-4 Induces class switch (IgM-IgE). Enhances MHC class II and Fc receptor expression.
* IL-5 acts on activated B cells to differentiate into Plasma cell (Ab secreting cells, not present in plasma).
* IL-13- similar function as IL-4
* IL-6 final differentiation of activated B cells into plasma cells
