Week 1: Immune System- Introduction

• Innate immunity


  Early phases of the host response, require no previous exposure to effectively respond to antigen, a variety of non-specific mechanisms
• Adaptive immunity


  Humoral (B cells) and Cell-Specific (T cells), antigen-specific lymphocytes are activated by co-stimulatory molecules that are induced on cells of the innate immune system after they encounter microorganisms, cytokines play an important role
• B and T cells are very specific for only one antigen. If they encounter the specific antigen and get stimulated, they replicated rapidly and carry out their function of eliminating the invading organism.
• Humoral immunity


  Antibodies (produced by B cells that differentiate into plasma cells), T cells help stimulation B cells, cytokines regulate Ig isotype switching
• Cell-mediated immunity


  Antigen-specific cytotoxic T cells (mostly CD8 T cells, but CD4 also work in some cases), Natural Killer cells help destroy intracellular pathogens
• Clonal expansion


  1. Clonal deletion

  2. Memory cell pool established
• Antibody


  Variable regions are antigen-binding sites, constant region comes in 5 main forms which are each specialized for activating different effector mechanisms
• Five classes of antibodies


  • IgG
  • IgA
  • IgM
  • IgE
  • IgD
• IgG


  Most common, present in body fluids and readily enters tissues, crosses placenta, protects against bacteria, toxins, viruses and activates the complement system
• IgM


  First circulating antibody to appear in response to an antigen, its presence indicates current infection, protects against bacteria, toxins and viruses
• IgE


  Involved in inflammation, allergic responses and combating parasitic infections, histamine is released from mast cells when IgE binds to known antigens
• IgA


  Secretary antibody, found in saliva, tears, colostrum, and lung, GI, prostatic and vaginal secretions, primary defense against local infections in mucosal tissues
• IgD


  Found on cell membranes of lymphocytes, is antigen for initiation of differentiation/maturation of B cells
• Immunoglobulin isotypes are selectively distributed in the body. IgG and IgM predominate in plasma, IgG and monomeric IgA are the major isotypes in extracellular fluid, Dimeric IgA predominates in secretions across epithlia, including breast milk, Fetus recieves IgD from mother through placenta, IgE is found mainly associated with mast cells just beneath epithelia surfaces (especially the respiratory tract, GI tract, and skin), The brain is normally devoid of immunoglobulin
• IgM antibodies appear early in the course of an infection and usually reappear, to a lesser extent, after further exposure. Presence of IgM can help diagnose a primary infection.
• Antigen


  Can react with antibodies or antigen-receptors on T and B cells, may or may not induce immune response
• Immunogen


  Antigens that elicit an immune response
• Hapten


  Too small to be immunogens by themselves but become immunogenic after combining with larger molecules that function as carriers
• Immune tolerance


  Unresponsiveness to antigens, does not mount an immune response to substances or tissues
• Allergen


  Antigens that induce an allergic response
• Passive immunity


  Transfer of preformed antibodies from an immune person to a non-immune person, provides immediate but temporary protection
• Active immunity


  Requires maturation and maintenance of memory cells (T cells and B cells) through active infection or immunization
• Vaccine types


  • Live, attenuated vaccines
  • Inactivated vaccines
  • Subunit vaccines
  • Toxoid vaccines
  • Conjugate vaccines
  • DNA vaccines
  • Recombinant vector vaccines
  • mRNA vaccines
• The Center for Biologics Evaluation and Research (CBER) regulates vaccine products.
• Immunization schedule is provided by the CDC.
• Active acquired immunity occurs when the body produces antibodies or develops immune lymphocytes against specific antigens, in this case varicella.
• Neonates are immunologically immature at birth, cell immunity is functional at birth but antibody production, phagocytic activity, complement activation are deficient. Maternal antibodies protect infant for 3-6 months-IgG only. With increasing age, T cell function decreases more so than B cell function, and there is a decreased ability to respond to antigenic stimulation as well as an increase in autoantibodies.