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Immune system and cell recognition - Coggle Diagram
Immune system and cell recognition
Defence mechanisms
non-specific:
immediate response that is the same for all pathogens
physical barrier e.g. skin
phagocytosis
Specific:
slower response as it is specific to each pathogen
cell-mediated response - T lymphocytes/cells
humoral response - B lymphocytes/cells
lymphocytes:
each one recognises a different chemical shape
collide almost exclusively with body's own material
some have receptors that fit those of the body's own cells - die or are supressed
only ones left respond to foreign material
in adults - produced in bone marrow, initially only come across self AGs
any that show a response to self AGs undergo apoptosis (cell death)
no clones of anti-self lymphocytes appear in the blood
Phagocytosis
phagocyte attracted to pathogen's chemical products - moves towards it along a concentration gradient
phagocyte has receptors on cell-surface membrane to attach to chemicals on pathogen's surface
Lysosome in phagocyte migrate to phagosome formed by emulsifying bacteria
lysosomes release lysozymes into phagosome where they hydrolyse the bacterium's cell wall, destroying it
Hydrolysis products of bacterium are absorbed by phagocyte into the cytoplasm
Cell mediated response
Involve T lymphocytes
AG presenting cells:
a cell that presents a non-self AG on their surface
infected cells present viral AG on their surface
Macrophage which has engulfed and destroyed pathogen, it will present the AGs on their surface
pathogen invades body and infects body cell
phagocyte places AGs from pathogen on surface
receptors on specific T helper cells fit exactly onto these AGs
the attachment activates T cells to divide rapidly by mitosis and form a clone of identical cells
T cells develop into memory cells, stimulate phagocytes to engulf pathogens, stimulate B cells to divide and secrete their ABs or activate cytotoxic T cells.
Cytotoxic T cells release a protein which embeds itself in the cell membrane creating a pore so anything can enter or leave, this causes cell death. Most common in viral infections as they infect body cells. Cells are sacrificed to prevent viral replication. e.g. sore throat - killer T cells killing body cells
Humoral response
involves B lymphocytes and ABs.
surface AGs of an invading pathogen are taken up by B cells
B cell processes AG and presents them on its surface
Helper T cells attach to the processed AGs on the B cell, activating the B cell
B cell now divides by mitosis to give a clone of plasma cells
cloned plasma cells secrete specific ABs that fits the AG on the pathogen's surface
AB attaches to AG on pathogen and destroys it.
some B cells develop into memory cells - can respond to future infections of the same pathogen by faster division and secretion of ABs
Antibodies
Proteins with specific binding sites synthesised by B cells. Reacts with specific AG on surface of non-self material. Made of 4 polypeptide chains - 2 heavy chains, 2 light chains. Binding site is different on each one so is called a variable region. Rest is the constant region - binds to receptors on B cells. Cause agglutination, clumps cells together making it easier for a pahgocyte to locate them as they are less spread out. Serve as markers which stimulate phagocytes.
Monoclonal ABs:
a single type of AB that can be isolated and cloned
Targeted meds:
Direct:
Cancers can be treated with them which are designed with a binding site complementary to the AG on the surface of a cancer cell. ABs attach to cancer cell, meaning other chemicals can’t bind to the cancer cell so it can’t divide.
Indirect:
attaching cytotoxic drug to monoclonal AB, when AB attaches to cancer cells it kills it, reduces harmful side effects of chemo
Can be used to diagnose diseases such as influenza, chlamydia, HIV, Covid-19, prostate cancer
Pregnancy testing:
placenta produces hormone hCG, found in mother’s urine. If hCG present in urine, monoclonal ABs on test strip bind to it. hCG-AB-colour complex moves along strip until trapped by a different type of Ab creating a coloured line.
Ethics:
creating them requires mice - deliberate induction of cancer in mice.
Patient should have all + and —. Testing presents dangers to humans
Vaccines
HIV