T-cell Activation: Antigen Presentation to B-cell Activation: Co-stimulation, Class Switching, and Maturation

T- and B-cell activation

Antigen-presenting cells, or APCs, include B cells, dendritic cells, Langerhans cells, and macrophages. Two signals are required for T-cell activation, B-cell activation, and class switching.

T-cell activation

1. APC ingests and processes antigen, then migrates to the draining lymph node.
2. T-cell activation (signal 1): exogenous antigen is presented on MHC II and recognized by Th (CD4+) cell. Endogenous or cross-presented antigen is presented on MHC I to Tc (CD8+) cell.

#boundingbox

3. Proliferation and survival (signal 2): costimulatory signal via interaction of B7 protein (CD80/86) on dendritic cell and CD28 on naive T cell.
4. Activated Th cell produces cytokines. Tc cell able to recognize and kill virus-infected cell.

#boundingbox

B-cell activation and class switching

1. Th-cell activation as above.
2. B-cell receptor-mediated endocytosis.
3. Exogenous antigen is presented on MHC II and recognized by TCR on Th cell.

#boundingbox

4. CD40 receptor on B cell binds CD40 ligand (CD40L) on Th cell.
5. Th cells secrete cytokines that determine Ig class switching of B cells.
6. B cells are activated and produce IgM. They undergo class switching and affinity maturation.

#boundingbox

Topics Covered:

• T-cell Activation: Antigen Presentation
• T-cell Activation: Co-stimulation and Function
• B-cell Activation: Antigen Uptake and Presentation
• B-cell Activation: Co-stimulation, Class Switching, and Maturation