Immune System

overview : reconnaissance, recognition and response
  • An animal must defend itself against unwelcome intruders—the many potentially dangerous viruses, bacteria, and other pathogens it encounters in the air, in food, and in water.
  • It must also deal with abnormal body cells, which, in some cases, may develop into cancer.
what are Two major kinds of defense that have evolved to counter  threats.?-the first kind of defense is innate immunity.
  • Innate defenses are largely nonspecific, responding to a broad range of microbes. 
  • Innate immunity consists of external barriers formed by the skin and mucous membranes, plus a set of internal cellular and chemical defenses that defend against microbes that breach the external barriers. 
  • The internal defenses include macrophages and other phagocytic cells that ingest and destroy pathogens.
the second kind of defense is acquired immunity 
    • Acquired immunity develops only after exposure to microbes, abnormal body cells, or other foreign substances. 
    • Acquired defenses are highly specific and can distinguish one inducing agent from another. 
    • This recognition is achieved by white blood cells called lymphocytes, which produce two general types of immune responses.
      • In the humoral response, cells derived from B-lymphocytes secrete defensive proteins called antibodies that bind to microbes and target them for elimination. 
      • In the cell-mediated response, cytotoxic lymphocytes directly destroy infected body cells, cancer cells, or foreign tissue. 
43.1 innate immunity provides broad defenses against infection
      • Microbes present in food or water, or those in swallowed mucus, must contend with the highly acidic environment of the stomach.
        • The acid destroys many microbes before they can enter the intestinal tract. 
        • One exception, the virus hepatitis A, can survive gastric acidity and gain access to the body via the digestive tract. 
  • phagocytic cells and antimicrobial proteins 
      • Microbes are destroyed within lysosomes in two ways.
        • Lysosomes contain nitric oxide and other toxic forms of oxygen, which act as potent antimicrobial agents. 
        • Lysozymes and other enzymes degrade mitochondrial components.
    • Four types of white blood cells are phagocytic. 
        • The phagocytic cells called neutrophils constitute about 60–70% of all white blood cells (leukocytes).
        • Another set of proteins that provide innate defenses are the interferons, which defend against viral infection.
    • Enhanced blood flow and vessel permeability have several effects.
      • First, they aid in delivering clotting elements to the injured area.
        • Clotting marks the beginning of the repair process and helps block the spread of microbes elsewhere. 
      • Second, increased blood flow and vessel permeability increase the migration of phagocytic cells from the blood into the injured tissues.
        • Phagocyte migration usually begins within an hour after injury. 
      • 43.2 in acquired immunity, lymphocytes provide specific defenses against infection 
    • Lymphocytes provide the specificity and diversity of the immune system.
          • The vertebrate body is populated by two main types of lymphocytes: B lymphocytes (B cells) and T lymphocytes (T cells).
            • Both types of lymphocytes circulate throughout the blood and lymph and are concentrated in the spleen, lymph nodes, and other lymphatic tissue. 
          • B and T cells recognize antigens by means of antigen-specific receptors embedded in their plasma membranes.
            • A single B or T cell bears about 100,000 identical antigen receptors. 
        • 43.3 humoral and cell mediated immunity defend against different types of threats! 
            • The immune system can mount two types of responses to antigens: a humoral response and a cell-mediated response.
              • Humoral immunity involves B cell activation and clonal selection and results in the production of antibodies that circulate in the blood plasma and lymph.
                • Circulating antibodies defend mainly against free bacteria, toxins, and viruses in the body fluids. 
              • In cell-mediated immunity, activation and clonal selection of cytotoxic T lymphocytes allows these cells to directly destroy certain target cells, including “nonself” cancer and transplant cells.
      • 43.4 The immune system’s ability to distinguish self from nonself limits tissue transplantation
              • to attacking pathogens, the immune system will also attack cells from other individuals.
              • One source of potential problems with blood transfusions is an immune reaction from individuals with incompatible blood types.
              • B antigens are found on type B red blood cells. 
              • Both A and B antigens are found on type AB red blood cells. 
              • Neither antigen is found on type O red blood cells.
        • 43.5 exaggerated , self - directed or diminished immune responses can cause diseases
        • Allergies are exaggerated responses to certain environmental antigens, called allergens.
        • Sometimes the immune system loses tolerance for self and turns against certain molecules of the body, causing one of many autoimmune diseases.
        • AIDS is another acquired immune deficiency. 
        • Healthy immune system function appears to depend on both the endocrine system and the nervous system