Lymphocyte Signaling

1. Lymphocyte Signaling • What is signaling? • The present concepts in Transmembrane receptor mediated signaling pathways. • Antigen receptor complexes and signaling. • Signaling---Gene transcription • Other signaling pathways & Death.

2. Receptor Crosslinking

3. Receptor Clustering Activation of Signaling STI 571 Inhibitor of Abl, kit and EGFR tyrosine kinases. Very promising in clinical trials.

4. Protein Phosphorylation Creates Binding Sites for Adaptor Molecules Why Phosphorylation?

5. PLCg and the second messengers

6. Receptors & Adaptor proteins Recruitment STI571- Potent tyrosine kinase inhibitor

7. Activation of G proteins V-Ras

8. BCR Signaling Complex • BCR H & L Chains always • with Iga and Igb chains • on cell surface. • Iga & Igb are the actual • signal transducers. • The cytoplasmic tails of • Iga and Igb have ITAM • Motifs, essential for • Signaling.

9. TCR Signaling Complex • CD3- g, d, e. The acidic residues in the TM region interact with the basic residues in the TM of TCR chains. Each chain has one ITAM. • z chain expressed as a dimer is associated with TCR. No Ig domain. 3 ITAMS.

10. Immunoreceptor tyrosine-based activation motif (ITAM)t • YXX[L/V]X7-11YXX[L/V] The tyrosines are separated by about 13 amino acids. • ITAMs present in accessory chains associated with BCR, TCR and Fc receptors (Mast & NK cells) • Upon Ag binding the associated Src family tyrosine kinases phosphorylate ITAMs which then become the binding sites for other signaling molecules.

11. Src family tyrosine kinases phosphorylate ITAMs • Src family B cells- Src, Blk, Fyn T cells- Fyn, Lck • Fatty acid • Receptor clustering results in kinase activation leading to ITAM Yp.

12. Regulation of Src Kinase activity • Kinase Domain • Y at NT- activation • Y at CT- negative • CD45- phosphatase dephosphorylates CT Y activates LCK • CSK- phosphorylates CT Y

13. TCR/Coreceptor clustering • Recruitment of the T cell specific Syk Family member-Zap 70 • Zap70 -/- • SCID

14. B-cell Co-receptor Complex • CD19- B cells CD19 -/- Deficient in B cell responses. • Physically associated • with CD21. • PI3-kinase. • CD21-complement receptor 2 • All increase BCR signaling by 1000-10,000 fold.

15. BCR clustering- Syk recruitment

16. BCR Signaling Receptor clustering results in a signaling cascade that culminates in the nucleus, activating specific gene transcription.

18. TCR Signaling

20. MAP Kinase Cascade

21. MAP Kinase Pathways

22. NFAT • Nuclear Factor of Activated T cells • Present in cytosol in resting cells and is • phosphorylated. In activated cells, Calcineurin • dephosphorylates NFAT resulting in translocation to nucleus and in conjunction with AP1 activates gene transcription. • Cyclosporin and FK506 (tacrolimus)- inhibit calcineurin & since T cells express maximum NFAT, T cells are suppressed. Routinely used to prevent graft rejection.

23. Other receptors that use ITAMs

24. ITIMs • Immunoreceptor Tyrosine based Inhibitory Motif • I/VXXYXXL • FCgRIIB-1: In Rh- mothers carrying Rh+ fetus, the activation of Rh-antibody- producing B cells can be prevented by injecting mother with anti- Rh IgG. • CTLA4 binding to SHP-2

25. TIR (Toll/IL-1R) domain

26. Signaling through Chemokine Receptors

27. Signaling through Chemokine Receptors

28. Cytokines & STATs

29. Fas Mediated Death Pathway- Apoptosis

30. Anti-apoptosis & BCL-2 Family

32. Summary Receptor clustering Adapter molecules Tyrosine kinases Antigen receptors take the help of coreceptors for signaling ITAM ITIM Cytokine receptors Toll receptors TNFR and cell death BCL-2 family and cell death