exam revision - responding to antigens

Question 1

define pathogen

Answer 1

disease causing cellular or non cellular agent

Question 2

define infection

Answer 2

invasion and/or growth of a harmful agent

Question 3

define carrier

Answer 3

an individual that is a host to a pathogen but may not experience any symptoms

Question 4

define vector

Answer 4

an animal, usually insect, that transmits the pathogen from host to host

Question 5

What is the bodies system of defence against disease

Answer 5

1st line of defence (non specific) - PHYSICAL, intact skin, mucous membranes/ secretion, enzymes, hair, etc.
2nd line of defence (non specific) - CELLULAR, macrophages, dendritic cells, natural killer cells, mast cells, leukocytes
3rd line of defence (specific) - MICROBIOLOGICAL, production of antibodies from B cells.

Question 6

macrophages

Answer 6

phagocytic cells, large white blood cells, identify and eliminate pathogens by phagocytosis (engulfing them)

Question 7

neutrophils

Answer 7

most abundant white blood cells, phagocytic cells, first cell to arrive to site of infection, identify and mount phagocytic attack on microbes.

Question 8

mast cells

Answer 8

contains histamine, found in tissues close to external environment, release chemical signals that attract other cells, release chemicals to attract other cells and histamine to trigger an allergy reaction.

Question 9

dendritic cells

Answer 9

phagocytic cell, mainly in surface cells, mobile cells that identify pathogens and secrete antiviral cytokines.

Question 10

complement proteins

Answer 10

is a set of 30+ proteins in the blood plasma that can be activated by the presence of microbes or antibody antigen complex. They can; 1. opsonise pathogens, 2. attract phagocyte, 3. create pores in bacteria membrane to destroy them.

Question 11

natural killer cells

Answer 11

recognise and attack cells that lack self markers, induce programmed cell death (apoptosis)

Question 12

T helper cells

Answer 12

deliver cell mediated immune defences that include direct elimination of pathogens, infected cells, and other abnormal cells

Question 13

T cytotoxic cells

Answer 13

to monitor body cells for the presence of foreign antigens that have been generated within the body cell by intracellular pathogens.

Question 14

explain the first line of defence

Answer 14

a variety of physical and chemical barriers surround the body in order to make up the first line of defence in immunity. These barriers are non-specific or innate meaning they do not form any memory of the pathogens when attack occurs, and the defence pre-exists.
Examples of chemical barriers include; acids (stomach); enzymes (saliva); mucus (traps microorganisms); sweat (acid/ dehydration factor); sebum (secreted from glands/ contains antiseptic)
Examples of physical barriers include; intact skin; mucous membrane (line surfaces internal/ external); cilia (small hairs that filter air); earwax (trap pathogen)

Question 15

explain the second line of defence

Answer 15

includes cellular and non cellular components that act as non specific defences against pathogens. Defensive molecules include cytokines which act as signalling molecules of the immune system that act locally. interferons and complement proteins also are activated.
Cellular defenses such as phagocytes which engulf and digest foreign material (macrophages) and natural killer cells which target virus infected cells by releasing proteins that causes them to induce a programmed cell death.
Protective responses also occur such as inflammation from the release of histamine from mast cells, the prevention of blood loss from platelets and proteins, and a fever can be initiated.

Question 16

explain the third line of defence

Answer 16

two possible pathways can occur after the initial response of the immune system, which are specific immune responses. Cell mediated and humeral immunity.
Cell mediated immunity involves the use of T cells, which have specific T cell receptors which are activated by encountering a specific antigen that may be displayed on a macrophage or other immune response cell. After activation, T cells increase in size and multiply to produce cytotoxic T cells (killer T cells) which attack the specific foreign cells, and helper T cells, which release cytokines which stimulate the right B cells to divide into plasma cells, and to attract more phagocytes. Also memory cells are produced for the specific antigen to cause faster response the second time.
Humeral immunity involves the use of B cells, which have specific B cell receptors which can only be activated by a specific antigen. When the B lymphocyte binds with a specific antigen, a helper T cell is activated to bind to the B cell which is presenting the antigen that has binded to it, and interleukin is secreted. This interleukin is stimulates the B cell to divide repeatedly to form few memory B cells and many plasma B cells. The specialised plasma cells produce many specific antibodies that will attach to the stimulating pathogen, and these antibodies have many processes to render the pathogen harmless. The few memory cells that are produced will remain in circulation of the body for many years after the initial infection and produce small quantities of antibodies, this leads to faster response if the antigen is presented again.

Question 17

what are antigens

Answer 17

are a type of protein that are present on all types of cell, and they are different depending on the cell that is expressing them. They distinguish the cell type, including as self or non self. Humans have a cluster of genes on chromosome 6 (major histocompatibility complex MHC) that produce two types of antigens called human leakocyte antigens either class I or II. HLA class I are found on all human cells, while HLA class II are found on cells of the immune system. These distinguish the cell as self, if a cell does not have these antigens then they are recognised by the body as non self and the immune system is triggered.

Question 18

What is passive immunity

Answer 18

because infants are born with relatively weak immune responses, they are protected during the first few months of life by antibodies they receive from their mothers through the placenta or through breast feeding etc.

Question 19

what is active immunity

Answer 19

there are two ways to become immune to something, either to get the disease and survive, or to be vaccinated.

Question 20

What is a vaccine

Answer 20

vaccines work by injecting small amounts of antigens from a disease into the body (dead or altered micro-organisms). This triggers an immune response and antibodies and memory cells are produced. The memory cells mean that if there is a second intrusion with the antigen it would be vastly quicker response time due to the memory cells.

Question 21

what are autoimmune disorders including example

Answer 21

autoimmune disorders are diseases caused by the body producing an immune response against it’s own tissues. It appears that there is a genetic predisposition to develop autoimmune diseases in many cases. In some cases a bacteria or virus triggers an immune response, and the antibodies or T cells attack normal cells as they have some part of their structure that resembles a part of the infecting antigen.
Multiple sclerosis is an immune mediated disease in which the body immune system attacks the central nervous system

Question 22

What is hypersensitivity

Answer 22

hypersensitivity refers to an immune system response to an antigen that is beyond what is considered normal. It is a response to an external factor called an allergen (eg pollen, dust, nuts, eggs). The body responds to an allergen by sending an army of immunoglobulin E (IgE) which is an antibody specific for fighting allergens. The IgE attaches itself to mast cells which when activated by the allergen a second time releases histamine and cytokines into the surrounding environment which causes allergy symptoms such as a runny nose or a swollen windpipe.