B cells Flashcards
Where do B cells move after maturation?
Into the blood and lymphatics.
What is the main role of B cells in the humoral immune response?
To produce antibodies via plasma cells.
What are the two main signals required for B cell activation?
Signal 1 from antigen binding to BCR, and signal 2, which depends on the type of antigen (T-dependent or T-independent).
What are the three main mechanisms of antibodies in humoral immunity?
Neutralisation: Prevents bacterial adherence.
Opsonisation: Promotes phagocytosis.
Complement activation: Enhances opsonisation and lyses bacteria.
What provides Signal 1 in B cell activation?
Binding of the antigen (Ag) to the B cell receptor (BCR).
Which molecules are associated with the BCR for signalling?
Igα and Igβ, which activate intracellular kinases upon cross-linking.
How can Signal 1 be enhanced?
If the antigen has activated the complement cascade, producing C3b.
C3b binds to complement receptor 2 (CR2) on the B cell surface.
How do TI-1 antigens provide Signal 2 to B cells?
By binding to both BCR and additional receptors, such as TLR4.
What is unique about TI-2 antigens?
They have repeated epitopes, often polysaccharides, leading to extensive BCR cross-linking.
What type of antibody is produced in response to TI antigens?
Primarily IgM.
How do T cells provide Signal 2 to B cells for TD antigens?
Via CD40-CD40L interaction and cytokine secretion.
How do B cells act as APCs in TD antigen responses?
They internalise, process, and present peptides on MHC class II to CD4+ T cells.
What are the roles of CD40 signalling in B cells?
Protects centrocytes from apoptosis.
Induces isotype switching.
Facilitates somatic hypermutation.
Where do activated B and T cells migrate to form germinal centres?
To the B cell follicles in secondary lymphoid tissues.
What happens to B cells in germinal centres?
Rapid division to form centroblasts.
Somatic hypermutation of Ig genes.
Isotype switching.
