Cross-linking of multiple B cell receptors (immunoglobulins) by antigen is needed to activate B cell intracellular signaling
T cell independent antigens
Antigen with repetitive structure (e.g., lipopolysaccharides) cross-link B cell receptors in wider ranges as well as non-BCR structures on B cell surface, resulting in activation of B cell without T cell (T cell independent antigen)
T cell dependent antigens
Antigen of proteins cross-link B cell receptors but at the same time needs antigen presentation by TCR of CD4+ T cell onto pMHC class II on B cell via CD28 and/or CD40 co-stimulation
T independent
T dependent
Antigen
Repetitive structure
Protein
Ig class switching
Little→IgM main
Induce→IgG
Affinity maturation
Doesn't occur
Occur
B cell memory
No
Yes
B cell longevity
Long plasma cell
Short plasma cell
Affinity maturation at germinal center
Somatic hypermutation at dark zone of lymph nodes
Activation-induced cytidine deaminase (AID) induces random point mutations on V regions of both of heavy chain and light chain
Affinity maturation at light zone of LN
Follicular dendritic cells present antigens to select only B cells that randomly obtained affinitive BCR (Ig)
