Biology - Chapter 7 Dealing with Disease

Antigen

a molecule found on the surface of cells either self or non-self.

MHC I marker

found on all nucleated cells in the body

MHC II marker

found on specialised immune cells

Autoimmune disease

Failure to recognise self from non-self cells

Bacteria

Unicellular prokaryotic pathogens

Release toxin and cause cell lysis

Some are beneficial like in the GI tract

Fungi

Cellular, eukaryotic pathogens

yeast or mould that thrive in moist conditions and reproduce via spores

Protozoa

Cellular eukaryotic pathogens and require a host to feed on

Viruses

Non-cellular pathogens that require a host to replicate

Made up of RNA or DNA inside a capsid

Antigens mutate making it difficult for our immune system to respond quickly

Prion

Non-cellular pathogen made up of proteins

causes other proteins to misfold and infects brains of some mammals

Physical barriers in humans

intact skin

mucous secretions

hairs in the respiratory tract

cilia

Chemical barriers in humans

lysozymes in tears

acidic sweat

earwax containing antibacterial compounds

low pH in the female reproductive organ

Microbiological barriers in humans

bacteria on the skin, GI tract and female reproductive organ

Physical barriers in plants

thick bark

waxy cuticles

thorns

stomata closing

Chemical barriers in plants

tannins from tea

phenols

caffeine

other enzymes that disrupt the cell membrane of fungi

Phagocytes

Engulf cells with foreign antigens via phagocytosis

Phagocytosis

1. engulfing of foreign material

2. fusion of lysosome and phagosome

3. enzymes degrade foreign material

4. foreign material broken down to smaller fragments

5. antigen fragments are presented on the MHC II marker on a APC

6. leftover fragments released by exocytosis

Natural killer cells

Large granulated cells which target both abnormal cells and virus infected cells and release cytotoxic chemicals,perforin and granzymes, which create pores in the target cell and trigger apoptosis.

How do natural killer cells kill infected cells?

1. Natural killer cells scan for a MHC I marker

2. If present, the killer inhibitory receptor bind to the MHC I marker, preventing cell death

3. If not present, the natural killer cell does not bind with a MHC I marker and the killer activation receptor is activated

4. The cytotoxic chemicals, perforin and granzymes are released

5. Pores in the target cells

6. Apoptosis

Mast cells

detect injury and when stimulated, release histamine which causes inflammation

The inflammation response

1. pathogen enters the body via a cut or wound

2. platelets surround the area to prevent further entry of pathogens

3. injured cells release cytokines to attract neutrophils to engulf pathogens

4. Mast cells release histamine to cause vasodilation in neighbouring vessels which causes an increased blood flow to the site and increases the permeability for immune cells to enter the damaged tissue.

5. Vasodilation allows phagocytes such as macrophages and neutrophils to the injured site to phagocytose

6. Complement proteins are attracted to pathogens to assist phagocytosis

7. pus forms (dead immune cells)

8. response continues until the site is cleared of pathogens

Excessive inflammation

allergic reactions

Eosinophils

large, granulated cells containing toxic chemicals which help destroy pathogen that are too large to be engulfed through phagocytosis

Cytokines

Group of signalling molecules made of proteins which aids in communication between immune cells and helps protect against pathogens

Released by immune cells to help guide other immune cells to the site of infection

Interferons

Type of signalling molecule that is released by virus-infected cells and they interact with receptors on neighbouring cells causing them to undergo several changes that make them less susceptible to viral infections.

can block translation of virus-infected cell and prevents the spread

Complement proteins

Group of proteins in the blood that assists other immune cells by opsonisation, chemotaxis, and lysis.

Opsonisation

Stick to pathogens to allow phagocytes to recognise them as foreign

Chemotaxis

Attracts more phagocytes to the site of infection

Membrane attack complex (lysis)

Forms pores on the surface of a pathogen or foreign cell which ultimately leads to apoptosis

Fever

Rise in temperature in response to an infection to kill pathogen by elevating the temperature

helps the immune system by activating certain proteins that bolsters the body’s defences

however, prolonged fevers can have a negative effect since cells are not functioning at the optimal temperature.

Plasma B cell

Produces thousands of antibodies for a specific antigen

Memory B cell

Provides immunological memory

Memory T cell

Provides immunological memory

Cytotoxic T cell

leave the lymph node to kill the infected cells at the site of infection

Humoral response

1. An antigen on the surface of a pathogen interacts with a complementary B cell receptor of a naive B cell, selecting the B cell.

2. Antigen-presenting cell engulfs the pathogen and presents its specific antigen on its MHC II marker. A T helper cell with a complementary T cell receptor will interact with the antigen on the MHC II marker. Cytokines will be released by the selected T cell.

3. The cytokines signal the B cell to undergo clonal expansion and differentiation into memory B and plasma B cells.

4. Memory B cells provide immunological memory whilst plasma B cells produce thousands of antibodies that are complementary to the antigen on the specific pathogen.

Cell-mediated response

1. An antigen-presenting cell presents a specific antigen to a naive T cell with a complementary T cell receptor, selecting the T cell.

2. Antigen-presenting cell engulfs the pathogen and presents its specific antigen on its MHC II marker. A helper T cell with a complementary shape to the antigen on the antigen-presenting cell interacts with it, selecting the helper T cell. Cytokines are released by the T helper cell.

3. Cytokines signal the selected B cell to undergo clonal expansion and differentiation into memory T and cytotoxic T cells.

4. Memory T cells provide immunological memory. Cytotoxic T cells arrive at site of infection. The specific T cell receptor of the cytotoxic T cell locate the specific antigen of the infected cell. If a complementary antigen is located, it bind to the cell’s MHC I marker and will release perforins and granzymes to induce apoptosis.

Antibodies

Quaternary structures that assist in neutralising pathogens by activating complement proteins, immobilisation and opsonisation.

Activation of complement proteins

antibodies attach to pathogens to facilitate the actions of complement proteins like a membrane attack complex.

Immobilisation

Antibodies can restrict the movement of pathogens

Opsonisation (antibodies)

Antibodies can bind directly to the surface of pathogens making them easier to identify to phagocytose

Primary lymphoid tissues

Bone marrow and thymus

Secondary lymphoid tissues

Tonsils, spleen and lymph nodes

Lymphatic system

transports antigen-presenting cells to the secondary lymphoid tissues for antigen-presenting recognition and initiation of the adaptive immune system and produces B and T lymphocytes in the primary lymphoid tissues.