Lecture 15 & 16 : Immunity

Question 1

What is immunity and what types are their?

Answer 1

Immunity is the body’s ability to defend itself against infectious agents, foreign cells and abnormal body cells.

• innate and adaptive immunity

Question 2

What is innate immunity?

Answer 2

• first line of defence
• present before exposure to pathogen & effective from birth
• nonspecific,quick recognition and response to variety of microbes

Question 3

What is adaptive immunity?

Answer 3

• the second line of defense
• activated after exposure to pathogens
• pathogen specific
• retains memory

Question 4

What are the external and internal defenses of non-specific innate immunity?

Answer 4

External defenses:
- barriers to entry

Internal defenses:

• inflammatory reaction
• phagocytic and natural killer cells
• protective proteins

Question 5

Explain how the skin and mucous membrane are barriers to entry:

Answer 5

• Intact skin cannot be penetrated by viruses or bacteria except for small cuts
• the mucous membrane lining the digestive, respiratory and genitourinary tracts prevent entry of harmful microbes, with some cells secreting mucus, a fluid that traps microbes and particles.

Question 6

How does washing action and secretions act as barriers?

Answer 6

• the washing action of saliva, tears and urine inhibit infection by microbes
• secretions from sebaceous (oil) glands and sweat glands give the skin a 3-5 pH range, acidic enough to kill certain bacteria and prevent colonization by bacteria

Question 7

How does the stomach and upper respiratory tract as barriers? What else is a barrier?

Answer 7

• the URS is limed by ciliated cells that sweep mucus and trapped particles or microbes up into the throat, where they can be swallowed or coughed out.
• the acidic environment of the stomach destroys most pathogens before they enter the intestines
• harmless bacteria (normal flora) in the intestine also prevent colonization by pathogens

Question 8

what are the internal innate defenses and when are they activated?

Answer 8

• when external innate defenses fail, internal innate defences are activated
• inflammatory reaction
• phagocytic cell
• natural killer cells
• protective proteins

Question 9

How does an inflammatory reaction work?

Answer 9

• characterized by redness, heat, swelling and pain.
• mast cells release inflammatory chemicals (histamine and kinky) that dilate capillaries bringing blood to the site
• inc. permeability allows protein and fluids to escape into the tissue, causing swelling
• swollen area and kinins stimulate free nerve endings, causing pain

Question 10

How do phagocytes work?

Answer 10

• phagocytes attach to microbes and engulf them by endocytosis
• a vacuole is formed, fusing with a lysosome
• the lysosome kills microbes by producing nitric oxide and free radicals (toxic) that degrade them into smaller fragments
• the degraded products are secreted out by exocytosis

Question 11

How do Natural Killer cells work?

Answer 11

• NK cells patrol the body and attack virus infected cells and cancer cells
• stress-induced molecules are produced and are put on the surface of these cells
• NK receptor (killer activating receptor) recognized these stress induced molecules
• a positive signal is sent to enable the NK cell to kill the bound cell

Question 12

How do protective proteins work?

Answer 12

Lysozymes: present in saliva, tears and mucous secretions can destroy bacteria

Interferons ( a and b ) : produced by virus infected cells to protect non-infected cells (used to treat certain viral infections such as hepatitis C)

Question 13

What is the complement system?

Answer 13

• 30 proteins in plasma, that are activated by bacterial infections ( C5b) to participate in the inflammatory response by attracting phagocytes to the site of inflammation
• some complement proteins (C3b) bind to surface of pathogens and help the phagocytosis of the pathogen by macrophages and neutrophils
• other complement proteins (c5-c9) join to form a membrane attack complex that makes holes in the cell walls and plasma membranes of bacteria

Question 14

When is adaptive immunity activated ?

Answer 14

It is activated when innate immunity (external and internal) have failed to prevent an infection & consists of lymphocytes.

Question 15

What is an antigen?

Answer 15

• Antigen : any foreign molecule that is recognized by lymphocytes and induces a response from them
• most antigens are large molecules ( proteins and polysaccharides )
• the immune system is able to differentiate from self and non-self (antigens)

Question 16

What is the role of Lymphocytes in adaptive immunity?

Answer 16

• lymphocytes recognize antigens through antigen receptors attached to their plasma membrane
• so adaptive immunity thus requires this recognition of antigens by lymphocytes

Question 17

What occurs when lymphocytes interact with antigens?

Answer 17

• a specific defense, either a humoral immune response or a cellular immune response

Question 18

What is humoral immunity?

Answer 18

• B lymphocytes (from bone marrow) recognize antigens
• undergo activation and proliferation (mitosis) and differentiate to become plasma and memory cells
• plasma cells secrete antibodies for extra cellular pathogens
• called humoral due to presence of antibodies in body fluids (humor)

Question 19

What are antibodies?

Answer 19

• a glycolic protein produced in response to an antigen and binds with it via non-covalent interactions
• antibodies are also known as immunoglobulins
• 5 types : igM,igG,igG,igE and igD

Question 20

What is the structure of an antibody?

Answer 20

• Y shaped with two arms
• each arm has a heavy long polypeptide chain and a light short polypeptide chain with variable and constant regions.
• the antigen combines with the antibody at the antigen bonding site in and a lock and key manner and forms antigen-antibody complexes.

Question 21

What are the functions of an antibody?

Answer 21

• neutralize viruses and bacteria
• agglutinate bacteria (clump)
• inactivate toxins and soluble antigens
• facilitate uptake of pathogen and soluble antigens by phagocytic cells
• activate the complement system to kill the pathogen

Question 22

What is cell mediated immunity and what does it give rise to?

Answer 22

• CMI is mediated by T-cells (produced in bone marrow and mature in thymus)
• involves activation and colonial selection of T cells resulting in helper, cytotoxic and memory T cells.

Question 23

What is the process of CMI?

Answer 23

• T cells recognize antigens on surface of antigen presenting cells (APC) through T cell receptor, with help from self proteins ( major histocompatibility complex molecules )
• after recognition, helper T cells are activated and secrete cytokines that stimulate other cells

Question 24

What do these cytokines stimulate?

Answer 24

• helper T cells for proliferation by cell division
• B cells to proliferate and differentiate into plasma cells to secrete antibodies
• cytotoxic cells to proliferate and kill virus infected cells and cancer cells
• macrophages and neutrophils to kill intracellular pathogens

Question 25

What is immunization, and it’s two types and what are vaccines?

Answer 25

• immunization is used to provide immunity against disease using vaccines
• active immunization: long lived immunity
• passive immunization: short lived immunity
• vaccines are substances that do not cause disease, but contain pathogen specific antigens or antibodies

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Question 26

What is active immunization?

Answer 26

• the use of vaccines in the form or pathogen specific antigens which the immune system responds by activating T cells and/or producing antibodies
• leads to memory cell generation which respond faster and stronger next time pathogen is encountered

Question 27

What is passive immunization?

Answer 27

• the use of vaccines that contain pre-formed antibodies

- immediate short term protection ( few weeks to months )

Question 28

What are the protective effects of passive immunization?

Answer 28

• lgG antibodies ofpregnant