Understanding Antigens and Immunity

• The immune system safeguards the body from potentially harmful substances by identifying and responding to antigens.

Antigens

• Antigens are typically proteins found on the surfaces of cells, viruses, fungi, or bacteria.
• Toxins, chemicals, drugs, and foreign particles like splinters can also act as antigens.
• The immune system recognizes and attempts to eliminate substances containing antigens.
• The body's cells possess proteins that function as antigens, including HLA antigens.
• The immune system usually recognizes these antigens as normal and doesn't react against them.

Types of Immunity

Innate Immunity

• Innate immunity is a non-specific defense system present from birth.
• It provides protection against all antigens.
• It involves barriers that prevent harmful substances from entering the body, forming the first line of defense.
• Examples include skin, mucous membranes, stomach acid, and enzymes in tears and skin oils.
• Innate immunity also exists in protein chemical forms, known as innate humoral immunity.
• Examples include the complement system, interferon, and interleukin-1 (which causes fever).
• When antigens bypass these barriers, other parts of the immune system attack and destroy them.

Acquired Immunity

• Acquired immunity develops upon exposure to specific antigens.
• The immune system develops a defense specifically against that antigen.
• Vaccines induce acquired immunity without the need for a primary infection.

Passive Immunity

• Passive immunity is conferred through antibodies produced in another body.
• Infants acquire passive immunity via antibodies transferred from their mother through the placenta.
• These antibodies typically disappear between 6 and 12 months of age.
• Passive immunization can also be achieved through antiserum injections containing antibodies from another person or animal.
• It offers immediate but not long-lasting protection against an antigen.
• Immune serum globulin (for hepatitis exposure) and tetanus antitoxin exemplify passive immunization.

Components of the Immune System

• The immune system includes specific types of white blood cells, chemicals, and proteins in the blood (antibodies, complement proteins, and interferon).
• Some components directly attack foreign substances, while others assist immune system cells.
• Lymphocytes are a type of white blood cell, including B and T lymphocytes.
• As lymphocytes mature, they learn to differentiate between the body's own tissues and foreign substances.
• After formation, some B and T cells multiply, providing immune system "memory".
• This memory enables a faster and more efficient immune response upon subsequent exposure to the same antigen, often preventing illness.
• For instance, individuals who have had chickenpox or been vaccinated against it are immune to the disease.

Inflammatory Response

• The inflammatory response occurs when tissues are injured.
• Causes can include bacteria, trauma, toxins, or heat.
• Damaged cells release chemicals like histamine, bradykinin, and prostaglandins.
• These chemicals cause blood vessels to leak fluid into tissues, resulting in swelling.
• This process helps isolate foreign substances and prevent further contact with body tissues.
• The chemicals also attract phagocytes, which ingest germs and dead cells through phagocytosis.
• Phagocytes eventually die, and pus forms from dead tissue, dead bacteria, and dead and live phagocytes.

Immune System Disorders

• Immune system disorders arise when the immune response targets body tissue (autoimmune disorders like rheumatoid arthritis), is excessive, or is deficient (immunodeficiency, increasing infection risk).
• Allergies involve an immune response to substances typically harmless to most people.

Vaccination (Immunization)

• Vaccination triggers the immune response by administering small doses of an antigen (dead or weakened viruses or viral components).
• This activates immune system "memory" (activated B cells and sensitized T cells).
• Memory allows the body to react quickly and efficiently to future exposures.
• A functional immune response protects against many diseases, while an inefficient response can lead to disease development.
• An excessive, insufficient, or misdirected immune response results in immune system disorders.
• An overactive immune response can cause autoimmune diseases, where antibodies attack the body's own tissues.