6.7 Response to infection

Mode of action of macrophages,lymphocytes and neutrophils

Mode of action of macrophages,lymphocytes and neutrophils

Macrophages and neutrophils are both phagocytes (non specific immune response and inflammation)

Lymphocytes are involved in the specific immune response (humoral and cell mediated response)

Process of phagocytosis

1. Neutrophils or macrophage recognises foreign antigens on a pathogen (non-self)

2. The cytoplasm of the phagocyte then engulfs the pathogen,containing it in a phagocycotic vacuole

   (phagosome)

3. Lysosomes fuses with the vacuole and releases lysosomes ehuch break down the pathogen

4. Macrophage then combined the antigen with the MHC protein presenting the pathogens antigens on the cell

   surface

5. It then becomes an APC (antigen presenting cell)

6. Chemicals called cytokines are produced which signal more phagocytes to the area raising the temperature

7. This is the inflammatory response

B-cells

B cells

• They are mainly involved in the humoral responses

• They are produced in the bone marrow

• When mature they are found in the lymph glands

• They have membrane receptor proteins which are identical to antibodies (immunoglobulins)

T cells

T cells

• Mainly involved in the cell mediated response

• produced in the bone marrow a

• Mature and become active in the thymus gland

• T cell receptors bind to antigens on infected body cells, more T cells are then produced

B memory cells

B memory cells- provide immunological memory to specific antigens allowing for a rapid immunological response if the same antigen is present again

B effector cells

B effector cells - divide to form plasma cells which produce antibodies particular to antigens

T killer cell

T killer cells- produce chemicals and destroy body cells

T helper cell

T-heller cells- activate plasma cells causing them to produce antibodies against antigens ln pathogens, secrete opsonises tagging the pathogen for phagocytosis

T memory cell

T memory cells- part of immunological memory so if the same pathogen is encountered they will divide rapidly into t killer cells to destroy pathogens

T helper cell activation

• T cells have receptors on their cell surface

• These receptors bind to the antigen present on the surface of the APC activating the t cell

• These activated T cells will then carry out multiple functions, T helper, killer and memory function as well as

  secreting cytokines causing b cell differentiation

Humoral response

T helper cell activation

1. Pathogen is engulfed by a macrophage,into phagosome,lysosomes are released breaking down pathogen

2. Lysosomes break down the ingested pathogen into antigens

3. These antigens are presented on the surface of the macrophage with MHC proteins making the cell an APC

4. The T receptor cells bind to the antigen on the APC activating it

• B cells with surface antibodies specific to the pathogen bind to the antigen

• The B cell then engulfs the pathogen (phagocytosis) and displays its antigen in the surface of the cell using

  MHC proteins making it an antigen presenting B-cell

• The activated T helper cell with a complementary receptor bind to the APC, and then producing cytokines

• These cytokines stimulate colonial expansion of B cell into B memory and B effector cells

• B effector cells differentiate into plasma cells which produce antibodies (immunoglobulins)

• These antibodies can agglutinate pathogens making them clump together and easier to phagocytose

• They can tag antigens with opsonin making them easier to phagocytose

• And bread them down in cell lysis

• The memory cells provide an immunological response carrying specific antibodies for test pathogen if

  its encountered again

Cell mediated response

1. A pathogen invades a host cell

2. The host cell displays the pathogen is antigens on MHC molecules, making the cell an APC

3. Tea killer cells with the complimentary receptor will bind to the antigens on the MHC

4. Cytokines are released by activated T-helper cells, which stimulate T cells to divide by mitosis and produce

   more T killer cells or T memory cells

5. These T killer cells bond to the APCs and secrete an enzyme called perforin which breaks down and destroys

   the cell

Active immunity vs passive immunity

Active immunity is when antibodies are produced by the body as the result of an antigen

Passive immunity is the introduction of antibodies from another person or animal

Natural active vs natural passive

Natural active immunity is when you are exposed to an infection/ pathogen naturally e.g chicken pox and produce antibodies fo fight against them

Natural passive is when the antibodies are passed from the mother to her offspring through breast milk or the placenta

Artificial active vs artificial passive

Artificial active immunity is when the introduction of a pathogen into the body e.g vaccination causes an immune response

Artificial passive is when the antibodies themselves are injected onto the body

What is her immunity

When a large proportion of the population (80-90%) have been vaccinated against it makes the transmission of that vaccinated disease highly unlikely since there is a much faster secondary response I’d that disease is encounters again due to the immunological memory causes by B and T memory cells

What is the problem when a large proportion of the population isn’t vaccinated against

• A large portion of the population will be susceptible to infection

• Infection can spread rapidly in the population

• Pathogens may develop resistance to treatment/prevention measures due to a lack of vaccinations

• controlling the spread can be more difficult if no vaccines are made/people don’t take the vaccines