Innate body defense

Immunity

• All the defenses that protect us against disease constitute

Immune system

• refers to all the cells and tissues that protect us against pathogens or any cells different from our own normal cells.

• Several factors determine body immunity

• Preference to body tissues:

• Portal of Entry:

• Virulence:

• Dose:

• Predisposition to disease:

• Medical diseases:

Several factors determine body immunity

• Medical diseases:

• co-morbidities such as AIDS, diabetes, medications (chemotherapy) that can depress the immune system

Several factors determine body immunity

• Predisposition to disease:

• influenced by genetic make-up, general physical and emotional health, nutrition, living habits, and age.

Several factors determine body immunity

• Dose:

• the number of pathogens that invade the body which determine whether an infection develops.

Several factors determine body immunity

• Virulence:

• Organism’s aggressiveness to overcome host defences or the organism’s ability to produce toxins that damage the tissue cells.

Several factors determine body immunity

• Portal of Entry:

• Break in skin or mucous membrane, passage ways that lead into the urinary, reproductive, and digestive systems.

Several factors determine body immunity

• Preference to body tissues:

• Polio virus- nervous tissue

• Flu virus- respiratory mucosa

• HIV- T-lymphocytes

• Body defences can be categorized into …..

• Innate or non-specific defences:

• Adaptive or specific defences:

• Innate or non-specific defences:

• Inherited, therefore, readily available.

• Effective against all harmful agents.

• Responses are rapid, nonspecific.

• Adaptive or specific defences:

• Develop after exposure to a particular pathogen.

• Specific to a certain pathogen and not others.

• Response is slower, but can completely eliminate the pathogen, as well as prevent future infections by the same pathogen by leaving behind antibodies.

Note: They always work hand-in-hand to protect the body (they get fired like a double barrel gun)

Lines of defense

• •“Lines of defense” begin with simple outer barriers, and proceeds successively through progressively complicated responses until the ultimate defense mechanism, the specific or adaptive immunity is reached.

  • First line of defense

  • Second line of defense

  • Third / Final defense

The First Line of Defense: Innate barriers

• •Skin serves as a mechanical barrier as long as it is intact.

• •Mucous membranes act as barriers, trapping foreign material to their sticky secretions; the ciliated respiratory tract mucosa help sweep impurities out of body.

• •Body secretions- Acid pH of the skin, chemicals in the sebum, very acidic vaginal secretions, tears, hydrochloric acid in the stomach and enzymes in the saliva wash away microorganism and destroy invaders.

• •Digestive juices destroy many ingested bacteria and their toxins.

• •Certain reflexes aid in removal of pathogens- sneezing, coughing remove microorganisms from URT, vomiting and diarrhea remove ingested toxins and bacteria via feces.

Second Line of Defense: Phagocytosis

• Phagocytosis: by which worn out blood cells, bacteria, cancer cells, and other potentially harmful foreign substances are eliminated.

• Phagocytes:

  • Neutrophils

  • Macrophages are WBCs derived from monocytes after they enter the tissue spaces.

  • Histiocytes- found in skin, liver, lungs, lymphoid tissue, bone marrow and soft connective tissue throughout the body.

  • Dendritic or Langerhans cells are macrophages of the skin.

  • Kupffer cells are macrophages located in the lining of the liver sinusoids.

  • Dust cells are macrophages in the lungs where they ingest solid particles.

Second Line of Defence: Natural Killer Cell

Natural Killer (NK) Cells: are lymphocytes different from those active in specific immunity.

• Found in lymph nodes, spleen, Red Bone Marrow and blood.

• They can recognize body cells that have abnormal antigen patterns on their membranes, such as tumour cells and virus-infected cells, and can lyse and kill them on contact.

• They are not phagocytic but they attack the cell’s plasma membrane and release a lytic chemical called Perforins that will cause the plasma  membrane and nucleus to disintegrate.

Second Line of Defense

• Inflammation

• Cardinal signs of inflammation:

  • pain (dolor)

  • redness (rubor)

  • heat (calor)

  • swelling (tumor)

• Effects of inflammation:

1. (1)Prevents spread of damaging agents to nearby tissues.

2. (2)Disposes off pathogens.

3. (3)Sets the stage for healing.

Second Line of Defence:

• Inflammation Pt 2

• Inflammatory response:

  Local chemicals released at site of inflammation:

  Histamine and Kinins from mast cells- cause local vasodilation and heat, redness and swelling.

  Cytokines from resident immune cells which attract neutrophils and monocytes/ chemotaxis

  Where the chemical signal is the maximum, the neutrophils squeeze through the capillary walls, a process called diapedesis.

  Monocytes follow and they become macrophages which are responsible for the final disposal of cell debris.

  Prostaglandins from mast cells and neutrophils contribute to the pain.

Chemotaxis

• Migration of leukocytes and macrophages, in response to chemicals liberated at sites of tissue damage, whereby the cells are attracted (positive chemotaxis) or repelled (negative chemotaxis).

Diapedesis

• Movement of blood cells through capillary walls into tissue spaces.

Margination

• Process of adhesion of WBCs to the walls of damaged blood vessels.

Phagocytosis

• The process by which WBCs engulf and destroy microbes

Second Line of Defence: Fever

Fever considered to be a non-specific protective response.

Pyrogens: are chemicals secreted by the WBCs and macrophages exposed to pathogens / foreign cells.

• •An increase in body temperature above the normal range can be a sign that body defences are active.

Fever boosts the immune system in several ways:

◦ Stimulates phagocytes.

◦ Increases metabolism.

◦ Decreases pathogen’s ability to multiply.

• Normal average body temperature:

98.6 F

• Febrile –

• medical term for fever.

• Afebrile –

• medical term for no fever.

Second Line of Defence: Interferons

• Interferon are small proteins that diffuse during a viral infection, into nearby cells and bind to their membrane receptors, stimulating the synthesis of proteins that interfere with the ability of viruses to multiply within the still healthy cells.

• Pure interferons are produced by genetic engineering in microorganisms, and are made available for medical therapy.

• Interferons act non-specifically on cells of the immune system and boost the immune response.

  • This is used in the treatment of hepatitis, malignancies such as melanoma, leukemia, and Kaposi sarcoma, and autoimmune disorders, such as multiple sclerosis.

Second Line of Defence: Completements

Complement Proteins – are 20 inactive plasma proteins that are synthesized by the liver and circulating in the blood. They get activated as a response to infection. They bind to foreign cells and help phagocytes recognize and engulf them by a process called complement fixation.

On complement fixation  - complements bind to certain sugars and proteins on the foreign cell wall resulting in Membrane attack complexes that produces lesions, complete holes in the cell surface, allowing water to rush in causing the cell to burst.

Opsonization: is a process in which pathogens are coated with a substance called an opsonin, marking the pathogen stand out for destruction by the immune system. Once a pathogen has been marked, it is killed via one of two mechanisms: it may be ingested and killed by an immune cell or killed directly without ingestion.

Agglutination: Refers to the clumping and sticking together of cells or bacteria or other small particles so as to form visible aggregates.

Agglutination is one of the ways in which ANTIBODIES operate.