B cells Flashcards
Defining and essential event during B-cell development
Expression of antigen receptor
Antigen receptors in the form of Ig on B cells are the means by which lymphocytes sense presence of antigen
Genes coding for variable region of Ig
V(variable), D(diversity) ,J (joining)
Role of RAG (recombinantion activating gene)
Involved in VDJ rearrangement
Role of BAFF in B cell development
Mutations in BAFF or BAFF R abolish B cell development
in the transitional cells. Hence B cells not functional
Function of B-1 B cells
Predominant in foetus(liver and spleen)
Express unmutated Ig molecules with limited diversity
Respond strongly to carbohydrate and T independent Ag
Respond poorly to protein Ag
Secrete large amounts of natural IgM
Function -innate immunity, mucosal immunity
Function of B-2 conventional B cells
Bone marrow precursor
Consists of naive B cell and Memory B cell
Naive B cells characteristic
Have IgM, IgD CD5-/CD23+CD27- Lower affinity for Ag Short life span Lack expression of costimulatory molecules
Memory B cells
IgM, Ig G,Ig A -class switching CD27+,CD23+,CD5- Higher affinity for antigen Longer half life Lower threshold for activation Express co stimulatory molecules
Thymus independent antigens
Type 1 and Type 2 -provide rapid and specific humoral immunity against imp class of pathogens
Type 1 - intrinsic ability to induce B cell proliferation
polyclonal B cell activators
poor inducers of isotype switching,memory
eg: LPS
Type 2-Activate B cells by cross linking BcR
Invokes Ag specificity
Highly repetitive molecules
eg: Flagellin,bacteriall capsular polysaccahrides
Characteristics of Thymus dependendent antigens
Monovalent antigens
Requires direct contact with Th cells, interaction of CD40 on B cells with CD40L on Ag-spf T cells
Evoke primary and secondary immune responses,
immunologic memory, isotype switching and affinity maturation
Implicated in mechanism of immunity by vaccines
Mechanisms for self tolerance
Maturation arrest, receptor editing,death/deletion/anergy
Competition for survival signals (BAFF) in periphery
Competition for survival signals in GC (Ag,Tfh help)
CD marker for mature B cell
CD 20
Pan B cell marker -CD 19
CD 40 - B and T cell interaction
CD 21:3d -marker for EBV entry
Event in B cell development correlating with Pro B cell
Pro B cell -CD19, activates VDJ rearrangement
Pre B cell- Expression of cytoplasmic mu-express surface mu heavy chain and light chain
Immature B cell -allows coupling of mu to kappa and lambda
Mature B cell -downregulates VDJ, express IgM and IgD
Which immunoglobulins bind complement when binding to Ag
Ig G, Ig M
Most differentiating factor between antigen dependent and antigen independent B cell development
Somatic hypermutation
