Immune System Overview

Immunity

• The immune system protects the body from pathogens.
• The immune system includes various organs and cells.

Immune System Organs

• Lymph nodes
• Tonsils & adenoids
• Thymus
• Appendix
• Spleen
• Peyer's patches
• Bone marrow

Immune System Cells

• The innate immune system includes cells like:
  • Neutrophils
  • Mast cells
  • Natural killer cells
  • Eosinophils
  • Basophils
  • Macrophages
  • Monocytes
  • Dendritic cells
• The adaptive immune system includes cells like:
  • Memory T cells
  • Cytotoxic T cells
  • Helper T cells
  • B cells
  • Plasma cells
  • Memory B cells
• Hematopoietic stem cell
• Myeloid progenitor, Lymphocyte progenitor

Immunity: Actively Acquired

• Natural: Antibodies developed after the disease
• Artificial: Antibodies developed through vaccinations, possibly needing boosters.

Immunity: Passively Acquired

• Natural: Antibodies passed on through breast milk.
• Artificial: Antibodies passed on through injection

Types of Hypersensitivity Reactions

• Type I (Immediate): IgE-mediated, occurs within an hour, examples include anaphylaxis
• Type II (Cytotoxic): IgG or IgM-mediated, occurs over hours or days, examples include hemolytic anemia.
• Type III (Immune Complex): Immune complexes, occurs in 1-3 weeks, examples include serum sickness and SLE
• Type IV (Delayed): T-cell mediated, occurs in days to weeks, examples include asthma, contact dermatitis, poison ivy, and local reactions to bites/stings.

Allergies (Type I)

• Inappropriate immune response
• Symptoms include itching, hives, angioedema (swelling of the face, lips, tongue).
• Treatment includes antihistamines

Anaphylaxis (Type I)

• Two or more body systems involved, severe reaction
• Faster onset, usually worse reaction
• Treatment includes epinephrine, steroids, and antihistamines

Anaphylaxis Treatment

• Administer epinephrine (0.3 mg IM for adults, 0.15 mg IM for pediatrics).
• Autoinjectors (EpiPens) are used.
• Administration via the vastus lateralis muscle.

HIV

• Chronic infection harming the immune system.
• Transmission through sexual contact, blood and body fluids, perinatal transmission (pregnancy placenta) breastfeeding.
• Reducing transmission methods are a priority.

Stages of HIV and AIDS Illness

• Stage 0 (Acute): Normal lab values
• Stage 1 (Chronic): CD4+ count > 500
• Stage 2 (Worse): CD4+ count 200-499
• Stage 3 (AIDS): CD4+ count < 200
• The CD4+ T-cell count falling below 200 cells/mL defines AIDS.

Examples of AIDS-Defining Conditions

• Cytomegalovirus retinitis
• Pneumocystis jiroveci pneumonia
• Chronic intestinal cryptosporidiosis
• HIV-related encephalopathy
• Mycobacterium tuberculosis (pulmonary or extrapulmonary)
• Invasive cervical cancer

HIV Management

• Prevention of infection
• Monitoring CD4+ counts
• Antiretroviral drugs
• Safe sex practices (condoms, dental dams, water-based lubricants, latex gloves)
• Monitoring for other infections

HIV Pre-Exposure Prophylaxis (PrEP)

• Truvada (tenofovir/emtricitabine)
• Daily tablet
• Effective 7 days after starting
• Ineffective if two consecutive doses missed
• Monitor kidney function (renal function)
• HIV test every 3 months.
• Continuous safe sex practices.

Lyme Disease

• Bacterial infection transmitted by ticks ( Borrelia burgdorferi).
• Blacklegged/Deer tick (~Ixodes scapularis)
• Has three stages of illness
• Early Symptoms include flu-like symptoms, fatigue, skin rash (erythema migrans).
• Later stages involve arthritis, neurological problems, and cardiac issues.

Lyme Prevention and Early Detection

• Avoid heavily wooded areas and underbrush.
• Wear light-colored clothing, long sleeves, and long pants.
• Use insect repellent (DEET).
• Check yourself and pets for ticks.
• Remove ticks promptly.
• Report a bite to a physician.
• Wait 4-6 weeks to get tested by a provider.

Transplant Rejection

• Hyperacute Rejection: Minutes to hours after transplant, immune system triggers blood clots in the new organ due to unknown tissue incompatibility.
• Acute Rejection: 1 week to 3 months after transplant; immune system attacks the new organ due to inflammation in blood vessels of transplant organ. Treatable with anti-rejection medication.
• Chronic Rejection: Months to years after transplant; chronic inflammation and scaring of the transplanted organ leads to reduced blood flow and organ failure.