Humoral Immune Response Overview

Humoral Immune Response

• B cells differentiate to produce plasma cells that secrete antibodies in response to antigens
• B cells also produce memory cells to accelerate immunity upon re-exposure to the same antigen
• Antibodies, also known as immunoglobulins (Ig), are proteins in body fluids produced by plasma cells
• Five classes of immunoglobulins exist:
  • IgG: most abundant, offers protection against infections, transported from mother to fetus via the placenta
  • IgA: found in blood and fluids like tears, saliva, and digestive fluids, prevents microbial attachment to epithelial barriers
  • IgM: found in blood, largest immunoglobulin, first antibody produced during initial antigen response
  • IgE: mediator of allergic responses and defense against parasitic infections
  • IgD: function is to signal B cell activation, enabling B cell participation in immune defense

Function of Antibodies

• Antibodies protect against infections through direct and indirect mechanisms
• Direct mechanisms:
  • Neutralization: blocks antigen binding to receptors
  • Precipitation: converts soluble antigen into insoluble precipitate
  • Agglutination: clumping of particles
• Indirect mechanisms:
  • Antibody binding to antigens activates inflammatory response
  • Enhanced phagocytosis
  • Activation of the complement system leading to microorganism destruction

Cell-Mediated Immune Response

• Involves destruction of infected cells by cytotoxic T cells or destruction of intracellular pathogens by macrophages
• Two levels of protection:
  • First line of defense: skin and mucous membranes, physical barrier preventing foreign body penetration
    • Epithelial cells lining cavities and body surfaces secrete substances (mucus, sweat, saliva, earwax) to trap and destroy pathogens
    • Normal bacterial flora contributes to innate immunity
  • Second line of defense: activated upon foreign body breaching the first line or cell injury
    • Cellular components:
      • Phagocytes: neutrophils and monocytes (white blood cells) - neutrophils are rapid responders, initiating phagocytosis, monocytes mature into macrophages that supplement neutrophils
      • Natural Killer (NK) cells: recognize and eliminate virus-infected cells and abnormal cells (e.g., cancer)
    • Chemical mediators:
      • Cytokines: small proteins regulating immune and blood cell growth and activity, signaling the immune system

Immune Response

• Antigen presence triggers B and T cell activation and differentiation
• Occurs in lymphoid organs where antigen selectively binds to B or T cells
• Cytokines control differentiation and proliferation of selected B cells into antibody-producing plasma cells and selected T cells into cellular targets
• Memory B and T cells respond more quickly upon re-exposure to the same antigen

Phases of Immune Response

• Primary response:
  • IgM antibodies are released, followed by IgG against the same antigen
  • "Primes" the body's immune system
• Secondary response:
  • More rapid and robust antibody production than the primary response
  • Due to memory B and T cells that do not require further differentiation
  • IgG production is significantly elevated, making it the predominant antibody in this phase

Sexually Transmitted Diseases (STDs)

• STDs are infections acquired primarily through sexual contact.
• They are caused by bacteria, viruses, or parasites that can be transmitted through blood, semen, vaginal fluids, and other bodily fluids.
• STDs can also be transmitted non-sexually, such as from mother to child during pregnancy or childbirth, or through blood transfusions or shared needles.
• STDs can be asymptomatic, making prevention crucial.

Symptoms

• STDs may present with a range of symptoms or no symptoms at all.
• Signs that could indicate an STI:
  • Sores or bumps on the genitals, oral area, or rectum
  • Painful or burning urination
  • Discharge from the penis
  • Unusual or odorous vaginal discharge
  • Unusual vaginal bleeding
  • Pain during sex
  • Sore, swollen lymph nodes, particularly in the groin
  • Lower abdominal pain
  • Fever
  • Rash on the trunk, hands, or feet
• Symptoms may appear within days after exposure, but some STDs can remain dormant for years.

Causes

• Bacterial Infections:
  • Gonorrhea
  • Syphilis
  • Chlamydia
• Parasitic Infections:
  • Trichomoniasis
• Viral Infections:
  • HPV (Human Papillomavirus)
  • Genital Herpes
  • HIV (Human Immunodeficiency Virus)

Prevention

• Wait and Test: Delay sexual contact with new partners until both have been tested for STIs.
• Safe Practices:
  • Use latex condoms or dental dams for oral, vaginal, and anal sex.
  • Prevent skin-to-skin contact between oral and genital mucous membranes.
• Vaccination:
  • HPV, hepatitis A, and hepatitis B vaccines are available.
  • Early vaccination before sexual exposure is most effective.
• Consent: Consent is crucial for preventing STDs.
• Barrier Contraception: Use condoms consistently and correctly.
  • Never use oil-based lubricants with latex condoms or dental dams.
  • Non-barrier contraception (such as birth control pills or IUDs) does not protect against STIs.

Diagnosis

• Sexual History: Taking a detailed sexual history is essential for diagnosis.
• Physical Exam:
  • Physical or pelvic exams to check for signs of infection (rash, warts, discharge).
• Laboratory Tests: Confirm diagnosis and identify coinfections.
  • Blood Tests:
    • HIV diagnosis
    • Later stages of Syphilis
  • Urine Samples: Some STIs can be confirmed with urine.
  • Fluid Samples: Testing of fluid from open genital sores can diagnose infection.

Treatment

• Bacterial and Parasitic STIs:
  • Often treated with antibiotics, usually in a single dose.
• Viral STIs:
  • Managed, but not always cured.
• Antiviral Drugs:
  • Used to manage herpes and HIV.
  • Daily suppressive therapy with antiviral drugs can reduce herpes recurrences.
  • Antiviral drugs can control HIV infection for many years, but the risk of transmission remains.
• Pregnancy: Immediate STI treatment during pregnancy can prevent or reduce the risk of infection in the baby.

Resources

• The Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine (ASHM) website provides information on how to take a sexual history.
• "Healthequitymatters.org.au" website provides information about HIV Law in Victoria.