Cell recognition and the immune system

Question 1

Lymphocytes

Answer 1

a type of white blood cell that identifies the presence of pathogens and potentially harmful foreign substances in the body to neutralise them and destroy them to prevent harm
* they can recognise millions of different antigens
* produced by stem cells in bone marrow
* 2 types: B-lymphocytes and T lymphocytes

Question 2

Non-specific defence mechanisms

Answer 2

reponse is immediate and the same for all pathogens, occcur whatever the infection
1. physical barriers
2. phagocytosis

Question 3

Specific defence mechanisms

Answer 3

reponse is slower and specific to each pathogen and specific responses to specific antigens
* provide long-term immunity
1. Cell mediated response- T-lymphocytes
2. Humoral reponse- B-lymphocytes

Question 4

Physical barriers

Answer 4

our bodies have defence mechanisms that reduce the chance of entry by a pathogen
1. Skin- made up of epidermis, structural barrier that produces sweat + sebum
2. Eyes- contain lysozymes which form tears,
3. Respiratory system- mucous membranes in lungs and nose trap nucous upwards through cilia, coughing and sneezing
4. Ear canal- lined with wax, which traps pathogens

Question 5

How do lymphocytes recognise self and non-self cells?

Answer 5

• 10 million different lymphocytes in body- each recognise different shaped antigen
• made when you are a foetus- unlikely to be exposed to any other cells than self cells
• lymphocytes complementary to antigens on self-cells die or suppress to prevent lymphocytes from attacking their own cells
• sometimes that process doesnt work and lymphocytes which attack their self-cells are produced
  1. Lymphocytes have a complementary receptor to the pathogens antigens
  2. Its stimulated to divide so its able to make more
  3. Clonal selection occurs
  —……………………………………………………………………….——

Question 6

Autoimmune diseases

Answer 6

immune system stops recognising ‘self’ cells and starts to attack healthy body tissue
* may be due to genetic tendancy in some families
* e.g. type 1 diabetes, rhematic arthritis, lupus

Question 7

Phagocytosis

Answer 7

Phagocytes engulf and recognise foreign pathogens
1. Chemical products of pathogen attract phagocyte
2. Phagocyte receptors attach to chemicals
3. Cytoplasm of phagocyte engulfs pathogen
4. Pathogen is contained in a phagosome (vesivle) in the cytoplasm of phagocyte
5. Lysosome fuses with the phagosme and the lysozymes (enzymes) inside break down/hydrolyse the pathogen
6. Phagocyte presents antigens by sticking them on its cell surface to activate other immune system cells

Question 8

Immune system

Answer 8

a group of cells, tissues, organs + membranes that defend an organism against pathogens and foreign substances

Question 9

Immune repsone

Answer 9

a complex series of specific and non-specific processes involving a range of cells and chemicals
* if body successfully fights an infection, it will respond more quickly and effectively if the same pathogen is re-encountered

Question 10

Why are lymphocytes specific..

Answer 10

• each type of cell has its own specific molecule on it’s cell that identify it
• molecules are usually proteins so their 3D tertiary structure enables lots of unique and identifiable shapes to be made

Question 11

Antigen

Answer 11

any part of an organism or substance that is recognised as non-self (foreign) by the immune system and stimulates an immune response
* usually proteins found on the surface of cells
* generates immune response by lymphicyte when detected in body
* triggers the production of an antibody

Question 12

B-lymphocytes

Answer 12

associated with humoral immunity, involving antibodies that are present in bodily fluids or ‘humour’
* mature in bone marrow
* there are many types, and each of them have their own specific antibody

Question 13

T lymphocytes

Answer 13

associated with cell-mediated immunity, immuntity involving body cells
* only respond to antigens that are presented on a body cell
* mature in the thymus gland
* receptors on T cell respond to single antigen

Question 14

Cell mediated immunity

Answer 14

T-lymphocytes respond to an organisms own cells that have been infected by non-self material from a different species e.g. virus
* respond to cells from other individuals that are genetically different
* have different antigens on their cell-surface membrane from the antigens on the organisms own cells

Question 15

Antigen presenting cells

Answer 15

any cell that presents a non-self cell on their surface
1. Infected body cells- present the viral antigens on their surface membrane
2. Macrophage- phagocytes engulf and destroy pathogens so present the antigens on their surface membrane
3. Cells of a transplanted organ- from individuals of the same species have different antigens on their cell surface membrane
4. Cancer cells- different from normal body cells so present themselves on their own cell surface

Question 16

Stages of T-lymphocytes/cell mediated immunity

Answer 16

1. Pathogens invade body cells/ taken in by phagocytosis
2. Phagocyte places antigens from pathogen on its membrane
3. Receptors on specific helper T cell fit onto these antigens
4. Attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
5. Cloned T cells-
   * develop into memory cells- enable rapid response to future infections by same pathogen
   * stimulate phagocytes to engulf pathogens by phagocytes
   * stimulate B cells to divide and secrete their antibody
   * activate cytotoxic T cells

Question 17

Cytotoxic T cells (T-killer cells)

Answer 17

kill abnormal cells and body cells that are infected by pathogens producing a protein called perforin that makes holes in the cell membrane
* holes mean cell membrane become freely permeable to all substances
* cell slowly dies

Question 18

Humoral immunity

Answer 18

involves antibodies

Question 19

Antibodies

Answer 19

proteins made up of 4 polypeptide chains that binds to an antigen
* produced by B-lymphocytes
* soluble in the blood and tissue fluid of body
* produces a specific antibody that responds to one specific antigen
* attaches to complementary antigen
* do not destroy the antigen directly, but instead prepare antigen for destruction:
* they cause aggulation of bacterial cells in this way clumps of bacterial cells are foremed, makinf it easier for phagocytes to locate them as they are lessspread-out within the body
* they serve as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached