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microbes
- microscopic living organisms. Most that live in animal bodies do not harm them and may be beneficial
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Pathogens
- microbes that cause disease (cholera, chicken pox)
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emerging infectious diseases
- New, more deadly strains of familiar pathogens (HIV, Ebola, SARS)
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Nonspecific Defenses
- Stomach: protein-digesting enzymes and extreme acidity
- Intestines: contain bacteria that destroy invaders
- Urinary tract: slight acidity of urine inhibits bacterial growth
- Vagina: acidic secretions and mucus
- Tears, urination, diarrhea, and vomiting all help to expel invaders
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Innate immune responses fall into three categories:
- 1) White blood cells (leukocytes): attack and destroy invading cells or the body’s own cells if they have been infected by viruses
- 2) inflammatory response: recruits leukocytes to the site of a wound and walls off the injured area, isolating the infected tissue from the rest of the body
- 3) Fever: is produced when microbes start a major infection in the body, which both slows down microbial reproduction and enhances the body’s own fighting abilities (phagocytes)
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Three important types of phagocytes are:
- Macrophages
- Neutrophils
- Dendritic cells
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2) inflammatory response
- causes tissues to become warm, red, swollen, and painful (mast cells release histamine)
- This defense mechanism has several functions:
- It attracts phagocytes to infected or injured tissue
- It promotes blood clotting
- It initiates protective behavior by causing pain
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3) Fever combats large-scale infections
- macrophages release pyrogen that raises the thermostat’s set point
- increases phagocytic activity and slows bacterial reproduction
- stimulates cells infected by viruses to produce a protein called interferon (stimulates natural killer cells)
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adaptive immune system: It consists of three major components:
- 1) immune cells
- 2) tissues and organs
- 3) secreted proteins
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1) Immune cells
- Macrophages and dendritic cells (both innate and adaptive immune responses )
- The key cellular players: B cells and T cells, which arise from stem cells in the bone marrow
- B cells: complete their development in the bone marrow
- T cells: migrate from the marrow to the thymus
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B cells
- complete their development in the bone marrow
- adaptive immune system
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T cells
- migrate from the marrow to the thymusAdaptive Immune System
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Adaptive Immune System
2) Tissues and organs
- lymphatic system vessels
- lymph nodes: contain masses of macrophages and specialized white blood cells called lymphocytes
- Thymus
- Spleen: that filters blood, exposing it to white blood cells that destroy foreign particles and aged red blood cells
- Tonsils: contain macrophages and other white blood cells
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Adaptive Immune System: Secreted proteins
- cytokines, that are used for communication between cells
- complement, assist the immune system in killing invading microbes
- B cells, produce antibodies that help the immune system recognize invading microbes and destroy them
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cytokines
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- Adaptive Immune System
- 3) Secreted proteins
- that are used for communication between cells
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complement
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- Adaptive Immune System- secreted protiens
- assist the immune system in killing invading microbes
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All adaptive immune responses include the same three steps:
- Lymphocytes recognize an invading microbe and distinguish the invader from self
- They launch an attack
- They retain a memory of the invader that allows them to ward off future infections by the same type of microbe
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How Does the Adaptive Immune System Recognize Invaders?
- Antibodies and T-cell receptors recognize and bind to foreign antigens
- Antigens: molecules that can provoke an immune response, including the production of antibodies
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- T-cell receptors: only on the surfaces of T cells
- A T-cell receptor triggers a response in its T cell when the receptor binds an antigen on a cell that has ingested an invading microbe
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Antibodies and T-cell receptors are not tailor-made for antigens
- B and T cells do not design antibodies and T-cell receptors to fit invading antigens
- Instead, the immune system randomly synthesizes millions of different antibodies and T-cell receptors
- Antigens almost always encounter antibodies or T-cell receptors that will bind them
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The adaptive immune system simultaneously launches two types of attack against microbial invaders:
- Humoral immunity is provided by B cells and the antibodies that they secrete into the blood that attack pathogens outside the body’s cells
- Cell-mediated immunity is produced by a type of T cell called the cytotoxic T cell that attacks infected body cells, killing both the cell and any pathogens inside it
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Humoral immunity
- adaptive immune system
- is provided by
B cells and the antibodies that they secrete into the blood that attack pathogens outside the body’s cells
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Cell-mediated immunity
- The adaptive immune system
- adaptive immune system
- is provided by
B cells and the antibodies that they secrete into the blood that attack pathogens outside the body’s cells
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Cell-mediated immunity is produced by cytotoxic T cells
- The body’s primary defense against cells that are cancerous or that have been infected by viruses
- Cytotoxic T cells in the blood may bump into an infected body cell that is displaying a viral protein on its surface
- The cytotoxic T cell receptor will bind to the viral protein and squirt proteins onto the surface of the infected cell, punching holes in the cell and killing it, sparing new body cells a future infection
- Cancerous cells also display unusual proteins that the cytotoxic T cells recognize as foreign, and are killed as a result
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Antibiotics
- chemicals that help to combat infection
- The occasional mutant microbe that is resistant to an antibiotic will pass on the genes for resistance to its offspring, which results in many antibiotics becoming ineffective in treating diseases
- Antibiotics are not effective against viruses
- Drugs are available that target different stages of the viral cycle of infection, and are used to treat HIV, severe herpes, and in some cases, the flu virus
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Vaccinations
- A vaccine stimulates an immune response by exposing a person to antigens produced by a pathogen
- Vaccines often consist of weakened or killed microbes, or some of the pathogen’s antigens
- an army of memory cells
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Allergies
are immune reactions to harmless substances that are treated as if they were pathogens
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autoimmune disease
- is an immune response against the body’s own molecules
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Immune deficiency diseases
- occur when the body cannot mount an effective immune response
- Severe combined immune deficiency (SCID), a group of genetic defects in which few or no immune cells are formed
- Acquired immune deficiency syndrome (AIDS), where a viral infection destroys a formerly functional immune system
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Severe combined immune deficiency
- a group of genetic defects in which few or no immune cells are formed
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Acquired immune deficiency syndrome (AIDS
- where a viral infection destroys a formerly functional immune system
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Cancer
- Natural killer cells and cytotoxic T cells encounter these new proteins, recognize them as non-self antigens, and destroy the cancer cells
- Some cancer cells do not bear antigens that allow the immune system to recognize them as foreign or, as in leukemia, suppress the immune system
- Vaccination can prevent some cancers
- Attempts to eliminate cancer mostly focus on surgery, radiation, and chemotherapy
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