IMMUNOLOGY Lecture 3

1. IMMUNOLOGYLecture 3 Jennifer E. Woodward, PhD E1545 Biomedical Science Tower 200 Lothrop Street 412-648-3926 woodwardje@upmc.edu

2. Outline Day 3 • Cell-mediated immune responses and effector mechanisms • Humoral immune responses and effector mechanisms

3. Cell-Mediated Immune Responses

4. Cell Mediated Immunity • Detect and eliminate cells that harbor endogenous (intracellular) antigens • Can recognize and eliminate cells such as tumor cells that have undergone genetic modifications so that they express antigens not typical of normal cells • Primarily T cell-mediated • Both antigen-specific and antigen-nonspecific cells can contribute to the response.

5. T cells 2 types of T cells • T Helper (TH) cells • CD4 glycoprotein • Provides help • T cytotoxic (Tc) cells • CD8 glycoprotein • Develop into effector cytotoxic T cells to kill tumor cells or virus-infected cell

8. Coreceptors in TCR Binding

9. Activation of TH cell by Both signal 1 and costimulatory Signal 2

10. Note: Activation of effector and memory T cells do not require the B7 molecule.

11. Engagement of the TCR by peptide-MHC initiates signal transduction

12. TCR-Mediated Signaling - 1 Engagement of MHC-peptide initiates processes that lead to assembly of the signaling complex

13. TCR-Mediated Signaling - 2 CD4/8 associated Lck phosphorylates ITAMS of coreceptors, creates docking Sites for Zap-70 ZAP-70 phosphorylates adaptor molecules that recruit components of several signaling pathways

14. TCR-Mediated Signaling - 3 1 – Phospolipase Cg (PLC) activation by phosphorylation 2 – Protein kinase C (PKC) activation By DAG and Ca2+ 3 – Ca2+-dependent activation of calcineurin

15. TCR-Mediated Signaling - 4 Activation of the small G protein, Ras

16. Exogenous superantigens are soluble secreted bacterial proteins (e.g.. endotoxins). Endogenous superantigens are membrane-embedded proteins produced hy certain viruses. These proteins crosslink the TCR and class II MHC by binding to all TCRs with a particular Vb sequence regardless of their antigenic specificity.

17. Humoral Immunity Can immunize with serum Ab Effective in eliminating exogenous (extracellular) Ag Interaction of Ag with B cell and the secretion of Ab = effector of the humoral immune response by binding to antigen and neutralizing or facilitating elimination Antibodies can be eliminated by • cross-linking Ag-Ab and then elimination by phagocytes • complement system activation with subsequent lysis of organism • neutralizing viral particles or toxins by coating and preventing binding to host cells

18. Maturation and Clonal Selection of B cells

19. Signal Transduction by an Activated B Cell Receptor (BCR) - 1

20. Signal Transduction by an Activated B Cell Receptor (BCR) - 2

21. B Cell Activation by T-dependent Antigen 1 – Ag crosslinks mIg generating signal 1, which leads to increased expression of class II MHC and costimulatory B7. The Ag-Ab complexes are internalized by receptor mediated endocytosis and degraded to peptides. Peptides are presented on membrane inside MHC class II. 2 – TH cell recognizes antigen-MHC class II complex on B cell and along with costimulation activates TH cell. 3 – TH cell begins to express CD40L. Signal 2 is provided by interaction of CD40 and CD40L. B7-CD28 interactions provide costimulation to the TH cell. 4 – B cells begin to express receptors for various cytokines. These cytokines when released from TH cells send signals for B cells to proliferate and differentiate.

22. Interactions of numerous cytokines with B cells generate signals required for proliferation and class switching during the differentiation of B cells into plasma cells. CD40/CD40L interaction is also required.

24. Concentration and Isotype of Serum Antibody following Primary and Secondary Immunization with Ag

26. Overview: Humoral and Cell Mediated Immune Responses TH cells recognize Ag presented on self molecules and respond by producing cytokines. Tc cells respond to Ag by developing into cytotoxic lymphocytes (CTL), which mediate killing of altered self-cells. B cell interacts with Ag and differentiates into a plasma cell. Secreted antibody (Ab) binds to the Ag and facilitates clearance

27. Cytokines

28. Cytokines exhibit autocrine and/or paracrine action. Fewer exhibit endocrine action.

29. Cytokines have attributes of pleiotropy, redundancy synergy, antagonism, and cascade induction.

30. Interaction of Ag with MØ and the subsequent activation of resting TH cells leads to release of numerous cytokines, generating a complex network of interacting cells in the immune response.

32. Cytokine-mediated generation And cross regulation of TH subsets

34. Hematopoietic cytokines and hematopoiesis

35. Effector Responses

36. Activities of the Complement System Complement – a group of serum proteins that participates in an ezymatic cascade, ultimately generating the membrane attack complex, which mediates cell lysis by making holes in the target cell.

37. Complement Activation Pathways

42. Generation of Effector CTLs Upon interaction with Ag-MHC class I complexes on target cells, CTL-Ps begin to express IL-2R and lesser amounts of IL-2. Proliferation and differentiation of Ag-activated CTL-Ps generally require additional IL-2 secreted by TH1 cells, resulting from Ag activation and proliferation of CD4+ T cells. In the subsequent effector phase, CTLs destroy specific target cells.

43. Antigen-activated memory CTL-Ps appear to secrete sufficient IL-2 to stimulate their own proliferation and differentiation into effector CTLs. These cells may not require help from TH cells or the CD28/B7 costimulatory signal for activation.

44. A TH cells may provide the IL-2 necessary for proliferation of an Ag activated naïve CTL-P when it binds to the same APC as the CTL-P.

45. Antibody-dependent Cell-mediated Cytotoxicity (ADCC) Non-specific cytotoxic cells are directed to specific target cells by binding to the Fc region of Ab bound to surface antigens on the target cell. Substances secreted by the nonspecific cytotoxic cells mediate target cell destruction.

46. Acute Inflammatory Response