Question

how can B cells be turned on using TI-2 ?

Answer 1

TI-2 antigens activate B-cells without direct participation of these antigents.These Thymus independent antigents are generally largw polymeric molecules with multiple ,repeating,antigenic dertermines.

Activation of B-cells requires binding of antigen to B-cell mIg.Antigen crossliks mIg,generating signal 1 which leads to increased expresson of class2 MHC and co-stimulatory B7.Antigen- antibody complexes are internalized by receptor -mediated endocytosis and degraded to peptides,some of which are bounded by class2 MHCand presented on the membrane as peptide MHC complexes.The TI-2 cell recognizes antigen -class 2 MHC on B-cell membrane.This interaction activates T-cells.Interaction of CD40( present on the b cell membrane) and CD40L(present on the T-cell membrane) provides signal 2 for B-cell activation .Interaction between B7 of B cell membrane and CD28 present on the T-cell membrane provide co-stimulation to the T-cell . In the presence of these signals,B-cell begins to express receptors for various cytokines released from T-cell.Binding of cytokines sends signals that support the differentiation. After receiving the activating signals ,the B-cells move into specialized regions of the lymph node or spleen to begin the process of differentiation into an antibody secreting plasma cells and memory B-cells..