B cell activation and regulation Flashcards
What is the difference between transmembrane antibodies and MHC molecules on CSM of B cells?
The MHC molecules present the antigens processed when the antibody binds to the pathogen.
Where is CD40 present?
On the CSM of all APCs
Where are B cells activated?
In the lymph nodes
Where are lymph nodes present?
Near major organs and tissues
Most likely for a foreign antigen to be picked up by APCs
What differentiates B cells from all other cells in the immune system?
Transmembrane antibodies
What is the BCR on B cells composed of?
IgM and IgD
BCR is a transmembrane antibody
What happens to naive B cells when they enter lymph nodes?
They mature and express IgG and IgD on their surface
What happens to the B cells that leave the lymph nodes without becoming activated?
They form short-lived plasma cells that synthesise and release non-specific antibodies like IgM
Where in the lymph nodes are T cells more abundant?
Paracortex
Where in the lymph nodes are B cells more abundant?
Cortex
What cells cause the initial activation of B cells in the lymph nodes?
APCs
T cells
Soluble antigens
Where in the lymph nodes do B cells mature?
In the germinal center
What are the two areas of the germinal center called?
Dark zone
Light zone
What happens in the dark zone of the germinal center?
Clonal expansion
Somatic Hypermutation
What happens in the light zone of the germinal center?
Affinity selection
Class switching
Differentiation
What are activated B cells called in the light zone of the germinal center?
Centrocytes
What are the activated B cells called in the dark zone of the germinal center?
Centroblasts
What do antibodies do?
Activate complement
Enhance phagocytosis
Activate and regulate inflammation
Which cells positively selects high affinity B cells in the germinal center?
T cells
Follicular dendritic cells
What is the germinal center in the spleen called?
Primary center
Which signals are used to cross-talk between T cells and B cells during their activation?
CD40 on B cells and CD40L on T cells
CD28 on T cells and CD80/86 on B cells
Cytokines - IL-4
What does the cytokine IL-4 do?
Upregulation of certain genes
Upregulate expression of ILR on surface of B cells (IL-receptors)
Triggers somatic hypermutation and increase SA of B cells
Forms immune-synapse
What are two B cell disorders?
Lymphoma - uncontrolled division of B cells
X-linked hyper-IgM - CD40 deficiency
What are possible treatments for B cell disorders?
Bone marrow transplant
Antigens neutralising cytokines
Transplant antibodies produced by healthy individual
Prophylactic use of antibiotics and antifungals
Avoid contact with infected people
What distinguishes regulatory B cells from other B cells?
They only produce IL-10
What happens when Bregs recognise T cells with the same antigen?
Fears this is an autoantigen
Produces IL-10
Prevents further differentiation of T effector cells
What are Natural regulatory T cells and T regulatory-1 cells examples of?
T cells that have been induced into their regulatory phenotype by B regulatory cells
Why do T and B cells not recognise the same antigen?
B cells recognise antigen via antibody that is internalised and processed
The antigen is broken down into peptides and presented on the B cell surface
T cells recognise antigens that are presented by APCs
The epitopes that the T cells recognise are therefore different to the epitopes on the antigens that B cells recognise
What is X-linked hyper-IgM syndrome?
Genetic mutation in B cells where there is decreased expression of CD40 on their CSM
