3.2 Antibody response and antibody-mediated immunity Flashcards
Where does antigen recognition by B cells occur?
Secondary lymphoid tissues
Use surface immunoglobulin antigen detection
How are B cells activated?
Naive B cells stop travelling and proliferate
Differentiation into antibody secreting plasma cells
In late stage infection - differentiate into memory B cells or plasma cells apoptosise
How do B cells recognise antigens and respond?
Secrete surface immunoglobulin receptors that recognise antigenic epitopes on pathogen surfaces in ECF
Triggers clonal expansion on B cells that differentiate into plasma cells
Plasma cells secrete antibodies into efferent lymph into blood
What causes lymph node expansion?
B cell proliferation
Where are plasma cells located?
Medullary cords of LNs
Some in bone marrow to secrete directly into blood
What are the two types of antibody response?
T cell dependant (protein antigen)
T cell independant (non-proteinaceous antigen)
Describe TI responses
Crosslink receptors on B cells to trigger a response
Only stimulate IgM production
Decribe TD responses
Requires cooperation between B cells and Th cells
- B cells recognises, processes and presents antigen
- Th cells provides cell:cell contact and secrete cytokines
Decribe TD responses
Requires cooperation between B cells and Th cells
- B cells recognise, process and present antigens
- Th cells provide cell:cell contact and secrete cytokines
B cells > plasma cells or memory cells
Class switching IgM > IgG
What happens in the LNs
Follicular DCs present antigens that stimulate naive T cells (clonal expansion and differentiation)
B cells enter LN via HEV and detect free antigens washed into LN and receive signals from Th2 cells
Primary focus develops in paracortex, B cells migrate from primary focus into follicle and germinal center develops
Plasma cells differentiate into secondary follicle and migrate into medullary cords
Antibody secreted > efferent lymph > blood
What is the difference between primary and secondary responses?
primary - first encounter with antigen (slow)
secondary - exposure to same antigen (faster and long lasting)
Describe Class Switching
Niave B cells only produce membrane bound Ig receptors (IgD and IgM)
Activated B cells/ plasma cells secrete soluble pentameric IgM
With T cell help, class switch IgM > IgG
Cytokine signals from innate immunity aids further class switching to IgA or IgA
Light chain and variable regions do not change
Polyclonal v Monoclonal
Polyclonal - Many different B cell clones react to multiple epitopes on antigen of pathogen
Monoclonal - highly specific to one epitope (used in diagnostic tests and immunotherapeutics)
What is Serology?
Measuring antibodies in serum to determine immune status of an animal
What is Immunoassay?
Using labelled antibodies as detection reagents
