rewritten notes for micro exam 3

K-DIS Disease and Meningitis

Introduction

K-DIS, associated with specific types of diseases, is most commonly known for causing meningitis in children under the age of 2, particularly before the late 1980s and early 1990s. The introduction of vaccines, particularly the Type B vaccine, significantly changed the incidence rates of this disease, which dropped from 50 to 100 cases per 100,000 children to less than 1 case per 100,000 children, marking a crucial public health success story.

Immunity and Immune Responses

Lines of Defense

  1. First Line of Defense

    • This includes unbroken skin, mucous membranes, pH levels, and secretions that serve as barriers to pathogens.
    • This line of defense is non-specific, meaning it does not target specific microbes.
    • It is considered innate, as we are born with it.

  2. Second Line of Defense

    • Also innate and non-specific, this line includes phagocytic cells, such as macrophages, and various inflammatory responses, including the production of antimicrobial molecules and fevers.
    • Phagocytic cells act similarly to Walmart greeters, treating all invaders the same.

  3. Third Line of Defense

    • This is characterized by a specific adaptive immune response, where the immune system recognizes foreign invaders and develops specific antibodies against them.
    • This response possesses immunological memory, which allows quick reactions upon subsequent exposures to the same pathogen.

Phagocytosis and Pathogen Recognition

Toll-Like Receptors (TLRs)
  • Toll-Like Receptors (TLRs) are protein molecules embedded in cell membranes. They play a crucial role in the immune response by recognizing foreign molecules known as Pathogen Associated Molecular Patterns (PAMPs), which include components such as flagellin and peptidoglycan.
  • The interaction between TLRs and PAMPs initiates the process of phagocytosis.

Antigen Presentation

  • Macrophages serve as Antigen Presenting Cells (APCs). They identify foreign pathogens by recognizing their PAMPs using TLRs and then engulf them for processing.
  • Major Histocompatibility Complex (MHC) molecules are crucial for distinguishing self from non-self. All nucleated cells have MHC Class I, which displays self-antigens, allowing the immune system to recognize normal cells.
  • When a foreign invader is processed and displayed on MHC Class I, it is identified as abnormal, prompting destruction by Natural Killer (NK) cells.
  • MHC Class II molecules also play a role in presentation to T helper cells, leading to antibody production.

Antigenic Determinants and Immune Activation

  • An Antigenic Determinant (A.D.) or epitope is a specific part of the antigen recognized by the immune system.
  • When macrophages present processed antigens on MHC molecules, they serve as signals (like waving a flag) to T helper cells, which can then activate B cells to produce specific antibodies against these antigens.
  • T cell receptors on helper T cells recognize A.D.s, leading to the expansion of B cells that produce antibodies. This process can take about 2 weeks for antibody formation, but memory cells can respond more quickly to previously encountered A.D.s within 2-3 days.

Types of Immunity

  1. Active Immunity
    a. Natural Active Immunity: Acquired through infection; the body produces antibodies in response to the disease.
    b. Artificial Active Immunity: Acquired through vaccination, where the body is exposed to a harmless form of the antigen to stimulate antibody production.

  2. Passive Immunity
    a. Natural Passive Immunity: Antibodies transferred from mother to baby through placenta or breast milk.
    b. Artificial Passive Immunity: The introduction of antibodies from an external source, like a gamma globulin shot after exposure to certain diseases. This is generally a one-time dose and does not lead to long-lasting immunity.

Immunoglobulins (Antibody Types)

  • IgG and IgM are the primary immunoglobulins involved in the immune response.
    • IgM: The first antibody produced in response to an infection; it has 10 binding sites.
    • IgG: The most abundant antibody in circulation, released second with 2 binding sites, playing a significant role in opsonization (enhancing phagocytosis) and neutralization of pathogens.

Mechanisms of Action for Antibodies

  • Antibodies interact specifically with A.D.s, facilitating several immune processes, including:
    1. Opsonization: Marking pathogens for phagocytosis.
    2. Agglutination: Clumping pathogens to make them easier targets for immune cells.
    3. Neutralization: Binding to pathogens and blocking their harmful effects.
    4. Activation of the Complement System: A series of proteins that destroy foreign invaders.
    • The immune response is further improved by the memory cells which recall previous antigen encounters and produce rapid responses upon re-exposure.

Bacterial Pathogens and Disease Mechanisms

Bacillus and Clostridium

  • Endospores are produced by certain bacteria (e.g., Bacillus and Clostridium) in order to survive in harsh conditions.
  • The vegetative cells of Clostridium botulinum (a Gram-positive bacterium) secrete botulinum toxin, which blocks the release of acetylcholine (Ach) at the neuromuscular junction, leading to a decrease in muscle contraction and can cause flaccid paralysis. This paralysis can stop breathing.

Neisseria gonorrhoeae

  • Neisseria gonorrhoeae is a Gram-negative bacterium responsible for the sexually transmitted infection known as Gonorrhea (commonly referred to as 'The Clap'). It attaches to epithelial cells via fimbriae, forming biofilms, and can colonize various human tissues such as the genitourinary tract, as well as other mucosal surfaces including the eyes and nasopharynx.
  • The immune response to infection includes an influx of neutrophils that attempt to consume the pathogen, leading to the formation of pus, and is associated with a range of clinical symptoms including asymptomatic infection, urethritis, and pelvic inflammatory disease.
  • Resistance to antibiotics is common, and Neisseria gonorrhoeae often shows resistance to multiple drugs, including cefixime, ceftriaxone, azithromycin, and tetracycline due to acquired resistance plasmids.