T cell activation

T cell activation involves 3 signals:

Signal 1 = TCR : MHC-peptide

 * Co-receptor (CD4 or CD8) enhances TCR signal
 * CD3 chains have ITAM motifs (conserved activation sequences)
 * Phosphorylated ITAM recruits ZAP-70, a cytoplasmic tyrosine kinase with SH2 domains that bind ITAMs
 * ZAP-70 signals TCR engagement

Signal 2 = CD28 : B7.1/.2 (co-stimulation)

 * CD28 signalling activates JNK

Signal 3 = Cytokines secreted by DC

 * Polarize to specific effector type

Summary
 * Note: effector T cells do not require co-stimulatory signals

(TCR : MHC-peptide → ZAP-70) + (CD28 : B7 → JNK )

→ NFκB, AP-1, NFAT → IL-2 → proliferation