Immunology Basics: Immunity Types

Adaptive Immunity vs. Innate Immunity

• Adaptive immunity is specific and acquired, responding to threats through B and T cells.
• Innate immunity is nonspecific and provides a general defense against pathogens.

Humoral vs. Cellular Immunity

• Humoral Immunity: Focuses on extracellular threats, involving B cells that produce antibodies to neutralize pathogens.
• Cellular Immunity: Targets intracellular threats, involving T cells that directly destroy infected cells.

Immunizing Event

• An immunizing event triggers the immune system to develop defenses against a specific pathogen.
• This results in B and T cell activation, replication, and differentiation into effector cells.
• Memory cells are also produced, providing faster and stronger responses to future exposures.

Primary and Secondary Immune Responses

• Primary Response: The initial encounter with an antigen, leading to activation and differentiation of B and T cells.
• Secondary Response: A faster and more robust response due to the presence of memory cells from the primary response.

Antigens

• Antigens are molecules on cell surfaces that identify cell type.
• Antigens can trigger immune responses, and antibodies target specific antigens for destruction.

Immunoglobulins (Antibodies)

• Immunoglobulins are soluble proteins produced by B cells or plasma cells.
• Five major classes: IgM, IgG, IgA, IgE, IgD.
• IgG: Predominant antibody in circulation, protects against bacteria, toxins, and viruses.
• IgM: First antibody produced during an infection; important in ABO blood group reactions.
• IgE: Involved in allergic reactions.

Natural vs. Artificial Immunity

• Natural Immunity: Acquired through normal biological experiences.
• Artificial Immunity: Acquired through medical procedures (e.g., vaccines).

Active vs. Passive Immunity

• Active Immunity: Acquired when the body produces its own immune response to an antigen.
• Passive Immunity: Acquired when antibodies are transferred from another source, providing temporary protection.

Vaccines

• Vaccines provide artificial active immunity.
• Types of Vaccines:
  • Attenuated: Weakened live version of a pathogen.
  • Inactivated: Killed version of a pathogen.
  • Subunit: Contains pieces of a pathogen.
  • Recombinant: Contains a modified version of a pathogen gene.
  • Virus-like particle (VLP): Resembles a virus, but lacks genetic material.
  • Polysaccharide: Made from molecules in pathogen capsules.
  • DNA vaccines: Inject DNA coding for antigens.

mRNA Vaccines

• Utilize mRNA enclosed in lipid nanoparticles to deliver genetic material for antigens.
• Example: COVID-19 vaccines.

Reasons for Immunizing Infants

• To protect infants from serious diseases and help their immune systems develop.

Boosters

• Boosters are necessary to trigger a stronger secondary antibody response.

Vaccine Safety

• Vaccines are safe and effective and do not cause autism.
• Low vaccination rates contribute to outbreaks of preventable diseases.

Immunodeficiencies

• Congenital Immunodeficiencies: Present at birth due to genetic defects.
• Acquired Immunodeficiencies: Develop during a lifetime, like HIV/AIDS.

Hypersensitivity Reactions

• Involve exaggerated immune responses to typically harmless antigens.
• Types of Hypersensitivity Reactions:
  • Type I (Anaphylactic): Immediate, IgE-mediated reactions (e.g., allergies).
  • Type II (Cytotoxic): Antibody-mediated destruction of cells (e.g., transfusion reactions).
  • Type III (Immune Complex): Antigen-antibody complexes activate complement (e.g., systemic lupus erythematosus).
  • Type IV (Delayed Cell Mediated): T cell-mediated reactions (e.g., contact dermatitis).

Type I: Anaphylactic Shock

• Localized Anaphylaxis: Restricted to a specific area, less severe.
• Systemic Anaphylaxis: Affects cardiovascular and respiratory systems, potentially life-threatening.
• Epinephrine is used to treat anaphylactic shock.

Type II: Cytotoxic Reactions

• Antibody-mediated reactions that destroy cells via complement activation or macrophage action.
• Blood type incompatibility is an example.

Rh Factor

• Rh+ individuals have the Rh factor protein. Rh- individuals lack it.
• Rh- mothers can develop anti-Rh antibodies during pregnancy with an Rh+ fetus, potentially harming the fetus (hemolytic disease of the newborn).

Type III: Immune Complex Reactions

• Antibody-antigen complexes circulate in the blood.
• Immune complexes activate complement and cause inflammation.
• Examples: Serum sickness, systemic lupus erythematosus, rheumatoid arthritis.

Type IV: Delayed Cell-Mediated Reactions

• T cell-mediated reaction, delayed response (24-48 hours).
• Example: Contact dermatitis.

Autoimmune Diseases

• Occurs when the immune system attacks self-antigens.
• Causes: Loss of self-tolerance.
• Examples: Lupus, diabetes, multiple sclerosis, celiac disease.

Multiple Sclerosis

• Immune cells attack myelin sheath of nerves, leading to neurological damage.

Celiac Disease

• Autoimmune reaction to gluten, damaging the small intestine.

Immune Complex Autoimmune Reactions

• Systemic Lupus Erythematosus: Autoantibodies attack DNA, affecting kidney function.
• Rheumatoid Arthritis: Autoantibodies target joints, damaging cartilage.
• Graves' Disease: Autoantibodies mimicking TSH causing hyperthyroidism.

Cell-Mediated Autoimmune Reactions

• Diabetes Type 1: T cells destroy insulin-producing cells in the pancreas.
• Psoriasis and Psoriatic Arthritis: T cells attack skin and joints.

Explore the differences between adaptive and innate immunity, and understand the roles of humoral and cellular immunity. This quiz examines immunizing events, as well as primary and secondary immune responses to pathogens. Test your knowledge on how the immune system responds to threats.