B Cells And Antibody Flashcards
Outline B cells
Are lymphocytes that develop in bone marrow (complete maturation within bone marrow)
Express unique antigen receptors (BCR or secreted antibody)
Plasma cells are activated B cells that secrete antibody
Memory B cells provide memory
Outline the origin and maturation of B and T cells
Both B and T lymphocyte precursors originate in bone marrow
Lymphocyte precursors destined to become T cells migrate (in blood) to the thymus and mature there. B cells mature in the bone marrow. During maturation, lymphocytes develop immunocompetence and self tolerance
Outline the structure of Antibodies
2 identical light chains, and two identical heavy chains
Antigen binding sites on Y ends, and transmembrane region at single end
Outline B cell receptors
The surface of each B cell is covered with approx 100,000 BCR (mainly IgM/IgD antibodies)
The BCR binds antigen and activates B cell (also need CD4 cytokines)
BCR is membrane anchored via a transmembrane domain. Secreted antibodies lack a transmembrane domain
What are the three functions of antibody
Neutralisation - binding viral protein, blocking interactions
Opsonisation - tastier to phagocytes/easier to phagocytise
Complement activation
What is viral neutralisation
Antibody binds virus and blocks viral protein/host interaction
What is opsonisation
Antibody binding bacterium makes more tasty/desirable for phagocytes. Phagocytes have antibody receptors
Outline activation of complement system and pore formation with antibody
Antibody bound microbe surface stimulates complement protein formation. Complement proteins form membrane attack complex, which in tern perforates foreign cell leading to cell lysis and death
Outline class, distribution, and function of IgG
Class of immunoglobulin (antibody).
Most abundant Ig class in blood - produced by B cells, circulates long period of time.
Functions - opsonisation/neutralisation. Only Ig class that crosses the placenta: provides passive immunity. Targets virus/bacteria
Outline the class, distribution, and function of IgA
Class of immunoglobulin (dimeric consists of secretory component and J Cain)
Distribution - present in secretions such as tears, saliva, mucus, and breast milk. Is monomeric form in blood.
Function - defence of mucous membranes, esp gut. Present in Brest milk. Confers passive immunity to nursing infant. targets virus/bacteria
Outline the class, distribution, and function of IgM
class of immunoglobulin (expressed monomeric form on naive B cell surface, pentameric form in blood stream)
Distribution - first Ig class produced after initial exposure to antigen. Expressed on naive B cells
Function - very effective in activating compliment (best antibody for compliment activation). Targets extracellular bacteria. Acts as antigen receptor (monomeric form on B cell surface)
Outline the class, distribution, and function of IgE
Class of immuno globulin (antibody) produced by B cells
Distribution - present in low blood concentrations
Function - Immunity to multicellular parasites. Allergic reactions
IgE activates mast cells (produce inflammatory mediators e.g. histamine) for parasite immunity and the allergic response
Outline the class, distribution, and function of IgD
Class of immunoglobulin (antibody)
Distribution - Expressed on naive B cells
Function - together with IgM, acts as B cell antigen receptor. Specific function unknown
What causes the formation of plasma cells
Stimulation of B cells by antigen + T cell leads formation of plasma cells
What part of antibody differs between antibody
The bottom, constant region. Region not in contact with antigen. Determines the mechanism used to destroy antigen, but not the antigen that it targets
