How does an immune system work?

 

The workings of a human immune system ?
All animals/organisms have an immune system – it is not unique to humans!

List some external barriers of the innate system that prevent infection
– invertebrates — exoskeleton (tough, dry barrier that keeps out bacteria and viruses)
– vertebrates — skin and mucous membranes

What cells are part of the innate system?
– neutrophils
– macrophages

neutrophils
functions in innate immunity as a type of phagocytic cell that tends to self-destruct as it destroys foreign invaders (most abundant type of white blood cell)

macrophages
a large, amoeboid, phagocytic white blood cell that functions in innate immunity by destroying microbes and in adaptive immunity as an antigen-presenting cell

What does activation of the complement system do to invading pathogens?
– complement system — group of about 30 different proteins that circulate in an inactive form in the blood
– these can act together (in complement) with other defense mechanisms — lysis (bursting) of invading cells, enhance phagocytosis, chemical signals to recruit more immune cells to the site of infection, some also trigger inflammatory response

Why is widening (dilation) and leakiness of blood vessels useful for an inflammatory response by the immune system?
dilation needed for interstitial fluid and neutrophils to migrate out of capillaries to the infected area

What chemical is responsible for dilation/leakiness of blood vessels?
– histamine

What are some clues that there is a systemic inflammatory process (infection) taking place in the body?
– redness, heat, and swelling (all localized)
– systemic — number of white blood cells increase, fever, septic shock (leakiness leads to widespread fluid accumulation in tissues and low blood pressure, which may lead to poor circulation to vital organs and organ failure)

Why is the inflammatory response considered part of the immune system?
because it mobilizes the innate immune response (neutrophils)

innate immunity
rapid response, recognizes broad ranges of pathogens, no “memory”

adaptive immunity
slower response, recognizes specific pathogens, has “memory”

Why does adaptive immunity differ from individual to individual?
depends on what pathogens they have been previously exposed to

antigen
a foreign (nonself) molecule that elicits and adaptive immune respone

antibody
a protein dissolved in blood plasma that attaches to a specific kind of antigen and helps counter its effects (secreted by plasma cells)

lymphocytes
a type of white blood cell that is chiefly responsible for the adaptive immune response and is found mostly in the lymphatic system

If you have swollen lymph nodes, what is likely going on in your body?
infection

What are two important features of adaptive immunity?
– it is highly specific
– has memory

feature of adaptive immunity: highly specific
antibodies attach to ONE particular kind of antigen and helps counter its effects (specific to that antigen…ineffective against any other foreign substances)

feature of adaptive immunity: has memory
it can “remember” antigens it has encountered before, sometimes even many decades earlier, and reacts against them more quickly and vigorously on subsequent exposure

What are two ways to achieve immunity to a specific pathogen?
– natural exposure
– vaccines (immunization)

active immunity
person’s own immune system actively produces antibodies

passive immunity
receiving pre-made antibodies…temporary because recipient’s immune system is not stimulated by antigens (only lasts as long as the antibodies do)

ex. fetus obtains mother’s antibodies through placenta before birth and after birth from breast milk

ex. injection of antivenom

What are the two types of lymphocytes?
– B cells
– T cells

B cells
completes its development in the bone marrow and is responsible for the humoral immune response

T cells
matures in the thymus…includes both effector cells for cell-mediated immune response and helper cells required for both the humoral and cell-mediated adaptive responses

humoral immune response
involves the activation of B cells and that leads to the production of antibodies, which defend against bacteria and viruses in body fluids (extracellular)

cell-mediated immune repsponse
involves the activation of cytotoxic T cells, which defend against infected cells (intracellular)

What happens after a selected B cell is activate?
– it grows and divides, forming identical cells specialized against the very antigen that triggered the response
– some of these B cells differentiate into memory cells
– others differentiate into effector cells (plasma cells)…these secrete antibodies into blood and lymph

Effector cells can be B or T cells, yet in the clonal expansion of B cells, effector cells that produce antibodies are specifically known as ___________ cells.
plasma

What is the role of memory B cells in the humoral response?
remain in lymph nodes, and can be activated by a second exposure to the antigen

Primary versus secondary humoral reponse
– primary response doesn’t start right away (usually takes several days for the lymphocytes to become activated by an antigen and form clones of effector cells
– secondary exposure — starts earlier, produces higher levels of antibodies, and is more prolonged

Antibodies themselves do not kill pathogens. How do they help to kill pathogens though?
– mark a pathogen by combining with it to form an antigen-antibody complex
– once marked, other immune system components bring about the destruction of the antigen

What type of cell is responsible for activating both the B cells (humoral response) and the cytotoxic T cells (cell-mediated response) of the adaptive immune response?
activated helper T cells

What type of cell does the helper T cell have to interact with to become activated?
antigen-presenting cell — binds to self-nonself complex

What does a cytotoxic T cell do to destroy infected body cells?
– releases perforin which makes holes in the infected cell’s membrane
– also releases enzymes that promote apoptosis — infected cell is then destroyed

Describe how loss of helper T cells (as in HIV/AIDS) causes a decreased ability to fight infection.
severely impairs the cell-mediated and humoral responses which drastically compromises the body’s ability to fight infections

Written by Lauren-Wiltsek