Specific internal defences Flashcards
Define an antigen
Found on a pathogen
Any substance capable of producing an immune response.
Explain how specific immunity involves non-specific cells.
Specific pathogen enters the body, which has a specific antigen which a specific antibody binds to, forming an antigen-antibody complex, thereby activating the immune response.
Immune response involves recruitment of non-specific cells (e.g. macrophages and lymphocytes)
Contrast B-lymphocytes and T-lymphocytes
B-lymphocytes
- produced in bone marrow
- mature in bone marrow
- “final” location is lymph nodes
T-lymphocytes
- produced in bone marrow
- mature in thymus
- “final” location is lymph notes
What are the two mechanisms of specific internal defence?
Humoral (antibody-mediated) and cell-mediated
What is the process of a humoral/antibody-mediated immune response?
Macrophage ID’s antigen as non-self
Engulfs antigen, breaks down w lysosomes
Becomes antigen-presenting cell
Travels in lymphatic system to lymph nodes
Presents to helper T-cell
Helper T-cells activate B-cells via chemokines
B cells are sensitised, enlarged and divide
Clones are produced from cloned B-cells
Clones become plasma cells (produce antibodies) and B-memory cells (assist in 2nd exposure)
Antibodies travel via bloodstream targeting specific antigens.
Antigen-antibody complex is formed.
Different antibodies target specific antigens through different mechanisms/
1) Coating bacteria (more easily ID’ed by phagocytes)
2) Agglutination (clumping of bacteria/virus/foreign blood cells, increases phagocytosis)
3) Soluble substances (mainly bacteria) become insoluble, more easily ID’ed by phagocytes
4) Dissolving bacteria
5) Inactivation of bacterial toxins (cannot attach to cells)
6) Prevents virus from uncoating (can’t inject DNA into cells)
What are the 6 mechanisms used by antibodies to target specific antigens?
1) Coating bacteria (more easily ID’ed by phagocytes)
2) Agglutination (clumping of bacteria/virus/foreign blood cells, increases phagocytosis)
3) Soluble substances (mainly bacteria) become insoluble, more easily ID’ed by phagocytes
4) Dissolving bacteria
5) Inactivation of bacterial toxins (cannot attach to cells)
6) Prevents virus from uncoating (can’t inject DNA into cells)
When would a humoral/antibody-mediated immune response be mounted?
Extracellular infection (bacteria + toxins) Incompatible blood transfusion
When would a cell-mediated immune response be mounted?
Intracellular infection (viral)
Cancer
Transplant
What is the process of a cell-mediated immune response?
1) Pathogen enters the body and is ID’ed as non-self by macrophages
2) Macrophage breaks down pathogen with enzymes from lysosomes, and displays antigen on cell membrane, becoming an antigen-presenting cell (APC)
3) APC travels through the lymphatic system and encounters a helper T-cell, which splits into clones (memory T-cells and more helper T-cells)
4) Helper T-cell clones release cytokines, which activate B-cell response and activate cytotoxic T-cells
5) Cytotoxic T-cells “search and destroy” infected cells. B-cells produce antibodies.
By what method, other than a cell-mediated immune response, can cytotoxic T-cells be activated?
Presence of an infected host cell, which displays the antigen on its surface.
How do cytotoxic T-cells work?
Travel in bloodstream to site of infected cells and secrete toxins which kill the cells on contact.
They can also trigger apoptosis.
What would be most likely to kill extracellular bacteria?
Macrophages (humoral response)
What would be most likely to kill intracellular bacteria?
Cytotoxic T-cells (cell-mediated response)
What are suppressor T-cells?
Suppress immune system to regulate its response.
What are memory T-cells?
Assist in secondary exposure to an antigen.
