MICR 304 Immunology & Serology Lecture 6 NK Cells, Lymphocytes Chapter 1.4 –1.17; 2.30 – 2.33
Overview of Today’s Lecture • Lymphoid cell lineage • NK cells and their receptors • Lymphocytes • Principles of cell signaling
Lymphoid Cell Lineage Naïve Lymphocytes IL2, IL7 IL15 Effector Lymphocytes NK cells
NK-Cells Form Part of the Innate Immune System • Large granular lymphoid cells • Develop in bone marrow (and maybe in the thymus?) • IL-15 dependent • Circulate in peripheral blood • Killinfected and tumor cells • Well documented role in defense against infections with viruses from Herpes family • Infections with Leishmania and Listeria • Tumor cells in vitro • Invariant receptors
Infections with Documented NK Cell Mediated Defense • Cytomegalovirus (CMV) • Herpes simplex virus • Cutaneous leishmaniosis (“Bhagdad Sore”)
Killing of Tumor Cells by NK Cells in vitro Tumor Cell NK-Cell t0 t60
NK Cells are an Early Component of Host Defense against Viral Infections Virus titer levels Virus titer decreases
Contributions of NK Cells to Defense against Virus Infections • NK cells control the initial infection until adaptive immune system can eliminate the virus • NK cells are activated by cytokines made by infected cells, macrophages and dendritic cells • INFa, IFNb, IL12, TNFa, • NK cells begin to kill infected cells • In addition, NK cells secrete IFNg activating macrophages and dendrictic cells, and driving immune response to TH1 type response • NK-DC cross talk
How do NK Cells Kill? • Triggered by two mechanisms • Antibody dependent cytotoxicity • Recognition of altered surface molecules • Mediated by: • Perforin • Pore-forming toxin • Permeabilizes target cell membrane • Granzymes • Enzymes • Induces apoptosis (cell suicide) • TNFa • Apoptosis Packaged in Granules
Antibody Dependent Cellular Cytotoxicity (ADCC) • NK cells recognize antibodies that are bound to target cells through FcgIII receptor (CD16) • CD16 is an activating NK cell receptor
NK Cells Recognize Altered Cell Surface • Depends on two types of receptors: • Activating (trigger cytotoxicity) • Direct recognition of changes in cell surface glycoproteins • Inhibitory • Normal MHC I • Balance of activating and inhibitory receptor signaling regulates NK cell responses • In normal cells, inhibitory receptors override activating signals
NK Cell Activation and Inhibition NK and normal cell: Inhibition > activation NK and abnormalcell: Activation uninhibited
Activating Receptors on NK Cells • Direct recognition of changes in cell surface glycoprotein • Short cytoplasmic tail • Associate with signaling adaptor proteins that initiate activation cascade • Example: NKG2D • Binds to proteins that are expressed in cellular stress
Inhibitory Receptors on NK Cells • Specific for various MHC I molecules • If MHC I is altered or down regulated inhibitory receptors do not bind and NK cells become uninhibited • Long cytoplasmic tail • Associates with inhibitory phosphatases • Example: KIR-2DL
Additonal Roles of NK Cell in our Immune System • Recent evidence suggests that NK cells contribute to the pathogenesis of hypersensitivity and autoimmune diseases (Bubnoff et al., 2010) • Cytokines released by NK cells influence disease development.
Active Learning Both neutrophils and NK cells can recognize their target cells through antibodies. In what are their responses to the target cells different?
Lymphocytes • Mediate adaptive immune responses Specific antigen recognition + Memory m m m m Clonal proliferation m m m
Lymphocyte Development IL15 IL2, IL7 Lymphoid Progenitor B-Lymphoblast T-Lymphoblast Prolymphocyte Thymocyte NK-Cells B-Lymphocyte Helper Cytotoxic Regulatory T lymphocyte Plasma cell
Adaptive Immune Responses • Antibody secretion (B-cells) • To block the invader • To enhance phagocyte and NK cell function • Activation of effector cells via cytokines (TH cells) • to better fight infection • Destruction of uncontrollable cells (CTL) • Infection by intracellular pathogens • Tumor cells • Control of immune response (Regulatory T cells)
From Antigen to Response • Specific antigen recognition • Common signal transduction Reaction nucleus
General Principle ofAntigen Receptors Receptor Signal transducer variable constant Cytoplasmic tail Cytoplasmic tail Intracellular cascade of signal transduction
Each Lymphocyte Carries only One Type of Receptor • “Billions of lymphocytes collectively carry millions of antigens”
Today’s Take Home Message • The lymphoid cell lineage gives rise to lymphocyte (IL2 and IL7 dependent) and to NK cells (IL15 dependent) • NK cells kill infected and tumor cells are the first producers of IFNg during an immune response. • NK cells are regulated by a complex balance of activating and inhibitory receptors. • Activating receptors like NKG2D recognize new surface molecules produced upon cellular stress. Inhibitory NK cell receptors like KIR-2DL bind to normal MHC I molecules. • Lymphocytes express antigen specific receptors and unlike other immune cells they undergo clonal expansion and development into memory cells.
Additional Resources • Zhou F.(2010) Expression of multiple granzymes by cytotoxic T lymphocyte implies that they activate diverse apoptotic pathways in target cells. Int Rev Immunol. 2010;29(1):38-55. • von Bubnoff et al. (2010) Natural killer cells in atopic and autoimmune diseases of the skin. J Allergy Clin Immunol. Jan;125(1):60-8. • http://education.vetmed.vt.edu/curriculum/vm8054/Labs/Lab6/IMAGES/MONOCYTE%20IN%20SMEAR.JPG