Chapter 24 The Immune System

About this Chapter Anatomy & function of immune system, organs, & cells How the body defends itself Non-specific body defenses Specific defenses that target one pathogen Combined defenses against bacteria and viruses Allergies and autoimmune problems

Immune System Functions: Overview of Defenses Scavenge dead, dying or abnormal (cancerous) body cells Protect from pathogens & foreign molecules Parasites Bacteria Viruses

Immune System Functions: Overview of Defenses Figure 24-1: Viruses

HIV or Human Immunodeficiency Virus

Life Cycle

Infectious Causes of Gastroenteritis. Bok K, Green KY. N Engl J Med 2012;367:2126-2132.

Genomic Organization and Atomic Structure of the Norovirus Capsid. Figure 1. Genomic Organization and Atomic Structure of the Norovirus Capsid. The RNA genome of the prototype norovirus strain, Norwalk virus (shown at the top), is organized into three open reading frames (ORF1, ORF2, and ORF3) that encode the designated nonstructural and structural proteins. Most diagnostic primers used in reverse-transcriptase–polymerase-chain-reaction assay target conserved areas in the RNA-dependent RNA polymerase region (NS7POL). VP1, the major capsid protein (shown below), is further organized into the N-terminal (N), shell (S), and protruding (P) domains defined by the indicated VP1 amino acid residues. The P2 region of the P domain (blue) is exposed on the surface of the capsid protein and is the site where histo–blood group antigens (HBGAs) (magenta) interact with the virion (dashed box). 5, 13 Bok K, Green KY. N Engl J Med 2012;367:2126-2132.

Body Defenses: Overview Physical barriers: skin & epithelial linings & cilia Chemical: acids, mucous & lysozymes Immune defenses – internal Innate, non-specific, immediate response (min/hrs) Acquired – attack a specific pathogen (antigen) Steps in Immune defense Detect invader/foreign cells Communicate alarm & recruit immune cells Suppress or destroy invader

Lymphatic System: Overview of Immune Defense Organs & Cells Bone marrow Thymus Lymph nodes Spleen Lymph vessels Leukocytes: (white blood cells – WBCs)

Lymphatic System: Overview of Immune Defense Organs & Cells Figure 24-2 ab: Anatomy of the immune system

Key Cells & Overview of their Function in Immune Defense Lymphocytes: helper, plasma, cytotoxic & natural killer (NK) Basophils Mast cells Monocytes Macrophages Neutrophils Eosinophils

Key Cells & Overview of their Function in Immune Defense Figure 24-4: Cells of the immune system

Innate Immunity: Phagocytosis & Inflammation Physical & chemical barriers Phagocytosis: macrophages, neutrophils, NK cells Engulf and digest recognized "foreign" cells – molecules Inflammatory response

Innate Immunity: Phagocytosis & Inflammation Figure 24-6: Phagocytosis

Cells of the Innate Immune System The Innate Leukocytes include: Natural killer cells Mast cells Eosinophils Basophils Phagocytic cells: including macrophages, neutrophils and dendritic cells, and All these cells function within the immune system by identifying and eliminating pathogens that might cause infection

Chemical factors produced during inflammation Histamine Bradykinin Serotonin Leukotrienes Prostaglandins sensitize pain receptors, cause vasodilation of the blood vessels at the scene, and attract phagocytes, especially neutrophils

Inflammatory Response: Cytokines Signal Initiation Histamines: from mast cells  swelling, edema, b. v . dilation Interleukins: fever, b.v. gaps  WBC's & proteins  infection Bradykinin: pain & swelling Membrane attack complex proteins

Inflammatory Response: Cytokines Signal Initiation Figure 24-8: Membrane attack complex

Acquired Immunity: Antigen-Specific Responses Activate T lymphocytes: direct attack Activate B lymphocytes to become: Memory cells: 20 immune response to that antigen Plasma cells: antibodies – attack that antigen

Antigen Presentation to Immature T Cells Antigen presentation stimulates T cells to become either "cytotoxic" CD8+ cells or "helper" CD4+ cells. Cytotoxic cells directly attack other cells carrying certain foreign or abnormal molecules on their surfaces. Helper T cells, or Th cells, coordinate immune responses by communicating with other cells. In most cases, T cells only recognize an antigen if it is carried on the surface of a cell by one of the body’s own MHC, or major histocompatibility complex, molecules.

T Cell Dependent B Cell Activation A TH2 cell (left), B cell (right), and several interaction molecules

B Cell Activation