Immunity and the Immune System

• Immunity is being insusceptible or resistant to a noxious agent or process, like a pathogen or infectious disease.
• Immunity can occur naturally or be produced by prior exposure or immunization.
• It is the body's natural or induced response to potentially infectious exposure.

Things to consider with immunity

• Immunocompetent patients
• Hypersensitivity
• Autoimmune disorders
• Immunodeficiency

Functions of the Immune system

• Protects the body from foreign antigens
• Identifies and destroys mutated "self" cells that could be harmful.
• It removes cellular debris, such as dead or damaged cells.

Organs of the Immune System

• Tonsils and adenoids
• Thymus
• Lymph nodes
• Appendix
• Bone marrow
• Spleen
• Peyer's patches
• Lymphatic vessels

Leukocytes (WBCs)

• Primary cells involved in both specific and non-specific immune responses.
• Derived from stem cells in bone marrow
• Uses the circulatory system to transport to the site of an inflammatory response.
• Normal number: 4,500-10,000 cells/mm3
• Leukocytosis happens in the presence of infection (> 10,000 WBCs)
• Leukopenia is when there are < 4500 WBCs

Types of Leukocytes

• Granulocytes make up 60–80% of leukocytes
• Granulocytes are derived from myeloid stem cells of bone marrow
• They are instrumental in the inflammatory response
• Protect the body from microorganisms
• The three types are neutrophils, eosinophils and basophils

Lymphocytes

• Bone marrow-derived lymphocytes (B Cells) are involved in humoral immune responses
• B Cells produce antibodies or immunoglobulins
• Thymus-derived lymphocytes (T Cells) participate in cellular-mediated immune responses
• T-cell activation occurs when macrophages recognize and present the T cell with a phagocytized antigen.
• Natural killer cells target virus-infected and tumor cells.

Antigens

• Chemical markers that identify cells
• Human cells have “self” antigens called human leukocyte antigens
• Foreign cell antigens will not match and are recognized as foreign and destroyed

Antibodies

• Immunoglobulins (Ig) or Gamma Globulins
• Proteins produced by plasma cells in response to foreign antigens
• Specific for only one antigen
• Label antigens for destruction
• There are five classes of human antibodies: IgG, IgA, IgM, IgD, IgE

Mechanisms of Immunity

• Cell-mediated immunity (T-cells) acts directly to destroy infection-causing pathogens (i.e., viruses, fungi, protozoans, cancers)without using antibodies but rather by activating phagocytes and T cells
• Humoral immunity (B-Cells) protects the body by circulating antibodies to fight against pathogens; the body's defense system produces specialized WBCs (leukocytes) to seek out and destroy invaders.

Antibody Responses

• First exposure to a foreign antigen stimulates antibody production in small amounts
• Second exposure to an antigen causes memory cells to make large amounts of antibody
• Vaccines are based on this principle
• Allergic responses happen when antibodies respond to foreign but harmless antigens

Types of Immunity

• Natural Active Immunity
• Artificial Active Immunity
• Natural Passive Immunity
• Artificial Passive Immunity

Natural Active Immunity

• After a person becomes ill with an infection, the body produces its own antibodies to fight the disease-causing organism and protect from future infection.

Artificial Active Immunity

• An immune response occurs when the body is exposed to weakened or dead pathogens in a vaccine.
• The body then makes T cells or antibodies that keep it from actually developing the illness.
• Vaccines are an example of this, like tetanus or measles

Natural Passive Immunity

• Immunity results when natural antibodies are passed from one body to another, like from a mother to a baby through the placenta or through breastfeeding.

Artificial Passive Immunity

• Protection from infection is achieved when a person receives serum from another person or animal that has already produced antibodies against the pathogen.
• Serum for treatment of rabies or botulism is an example.