Lecture note 20.pdf

10/29/20 Chapter 20 Infectious Disease and Human Immune System Infectious Disease • Illness resulting from the presence and growth of pathogens in an individual host organism • Synonyms: - Contagious diseases - Transmissible diseases 1 10/29/20 Infectious Agent • Pathogen – an organism...

10/29/20 Chapter 20 Infectious Disease and Human Immune System Infectious Disease • Illness resulting from the presence and growth of pathogens in an individual host organism • Synonyms: - Contagious diseases - Transmissible diseases 1 10/29/20 Infectious Agent • Pathogen – an organism that causes disease • Types: - Bacterial Viral Eukaryotic - • Bacteria: single-celled prokaryotes; diverse group; 3 basic shapes - Vast majority of bacteria are harmless or beneficial; only a few are pathogenic that secrete toxins Pili Gelatinous capsule Rod shaped (bacilli) Cell wall Plasma membrane Circular DNA chromosome Flagellae Spherical (cocci) Plasmid Spiral (spirochetes) 1 µm Figure 18.1 2 10/29/20 • Reproduction of bacteria: Binary fission: 1à2 à4à8 - Rapid Noon Chicken salad sandwich 2 bacteria - • Pathogenic bacteria: Mycobacterium tuberculosis - Streptococcus pneumoniae - Foodborne (E. coli, Salmonella spp.) 2:00 p.m. 128 bacteria 4:00 p.m. 8192 bacteria - 8:00 p.m. Over 33 million bacteria Figure 18.3 • Viruses: consist of nucleic acid (DNA or RNA) surrounded by a protein sheath or coat; no cell structure Surface protein Membrane envelope Reverse transcriptase Capsid 0.01 µm Genome: Single-stranded DNA or RNA or Double-stranded DNA or RNA Figure 18.4 3 10/29/20 • Reproduction of viruses: - Cannot reproduce by themselves - Hijack the host cell’s transcription and translation systems 3 2 1 RNA Reverse transcription DNA Host cell Transcription and translation 4 Viral genomes (RNA) Viral proteins Figure 18.5 • Pathogenic viruses: - Hepatitis viruses (A, B, C, D, E): several diseases of the liver, collectively known as hepatitis, are caused by DNA or RNA viruses - Influenza viruses: commonly referred to as the flu, an infectious disease caused by RNA viruses Hepatitis B Virus Influenza Virus 4 10/29/20 - Ebola virus: within the genus Ebolavirus, contain RNA, attack the liver cells, endothelial cells, and immune cells • Eukaryotic pathogens: some fungi and parasites (e.g. worms) can infect humans - Malaria: a mosquito-borne infectious disease of humans caused by eukaryotic protists (unicellular) of the genus Plasmodium within red blood cells 5 10/29/20 Transmission of Infectious Agents (a) Direct contact (c) Indirect contact (b) Vector-borne (d) Inhalation (e) Ingestion Figure 18.8 6 10/29/20 The Body’s Response to Infection • Innate immunity: one is born with and is continually ready to response • Acquired immunity: acquired by infection or vaccination • 3 lines of defense: - Skin and mucous membrane – Innate Macrophage – Innate Lymphocytes – Acquired - First line of defense: anatomical and physical barrier • Skin: - Shed: take pathogens with it Low pH: repel microorganisms Glands in skin: secrete chemicals to slow bacterial growth Pathogens 1 Nonspecific Skin 2 Nonspecific Macrophage 3 Specific • Mucous Membrane: - Mucous traps pathogens Can be sneezed, coughed away Lymphocytes Figure 18.9 7 10/29/20 Second line of defense: • Macrophages: certain types of white blood cells made in bone marrow - Engulf and digest invasive organisms (phagocytosis) - Digest old red blood cells and cellular debris - Release chemicals to stimulate production of more white blood cells Second line of defense: • Inflammation: a reaction producing redness, warmth, swelling and pain Mast cells release histamine to increase size of blood vessels - More blood arrives to speed cleanup and repair - Swelling occurs, causing pain by pressing against nearby nerves - • Fever: temperature above range of 97-99º F Macrophages release chemicals called pyrogens, which cause temperature to increase - Increased temperature inhibits bacterial growth - Increase metabolism of healthy cells - 8 10/29/20 Third line of defense: • • Lymphocytes: a type of white blood cells produced in bone marrow; recognize specific antigens - Antigens can be pathogens, pathogen-infected host cells, and other non-harmful particles - Travel throughout the body in the blood and lymphatic system Types of lymphocytes: named depending on where they mature - B lymphocytes mature in the bone marrow. - T lymphocytes mature in the thymus. Bone marrow stem cell Thymus Bone B cell Both B and T cells move through circulatory and lymphatic systems, collecting in the spleen and lymph. T cell Figure 18.14 9 10/29/20 • - B lymphocytes and Antibody-Mediated Immunity B-cell receptors B cell Antigen Recognize antigen and produce its antibody to rid it - Not directly kill host cells bearing the antigen - Make clonal copies of self, providing long-term immunity Antibodies Clonal population Figure 18.17 • T Lymphocytes and Cell-Mediated Immunity – recognize and attack the host cells bearing the antigen; enhance overall immunity Macrophage presents antigen to T cell. Viruses T cell T-cell receptors Virus antigen 1 Memory cells will help the body respond more quickly if the pathogen is encountered again. 2 Cytotoxic T cells attack and kill body cells that have become infected with a pathogen. Virus Clonal population Body cell Figure 18.18 3 Helper T cells secrete a substance that enhances humoral immunity (B cells) and cell-mediated immunity (T cells). Interleukin 2 amplifies immune response. 10 10/29/20 The Body’s Response to Infection • Passive Immunity – transfer of active immunity in the form of readymade antibodies Short-term, lasts as long as antibodies are in bloodstream - Natural: maternal transfer from mother to baby - Artificial: immunotherapy - • Active Immunity – self-developed by exposure to antigen and production of B and T cells Long-term - Natural: primary immune response - Artificial: influenza vaccine (attenuated or inactivated microbes) – Immunization or Vaccination - Auto-Immune Response • An overactive immune response against tissues and substances normally present in the body • Autoimmune diseases: - Rheumatoid arthritis: the immune system attacks the lining of the joints throughout the body and causes chronic inflammation - Diabetes type 1: the immune system attacks the cells that make insulin, a hormone for blood sugar control 11 10/29/20 Allergy • A hypersensitivity disorder of the immune system - Acquired, predictable, rapid - Excessive activation of certain white blood cells called mast cells by a type of antibody called Immunoglobulin E (IgE) - Allergen: a harmless substance in the environment that causes a reaction Acquired Immune Deficiency Syndrome (AIDS) • Human Immunodeficiency Virus (HIV) kills or disables helper T cells to cause immune deficiency - Opportunistic infections occur when the immune system is weakened - Transmission: contact with bodily fluids (semen, blood, vaginal fluids, and occasionally breast milk) 2 1 12