Chapter 5 Cell recognition and the immune system Flashcards
What is a phagocyte?
It is a macrophage (type of white blood cell) that carries out phagocytosis.
Describe the stages of phagocytosis
- Phagocytes are in blood and tissue and chemical or debris released by pathogens or abnormal cells attract phagocytes and they will move towards these cells.
-Many receptor binding points on surface of phagocytes. They will attach to chemicals or antigens on pathogen via these receptors.
-Phagocyte changes shape to move around and engulf pathogen.
-Pathogen contained with a phagosome vesicle.
-Lysosome within phagocyte will fuse with phagosome and release its contents.
-Lysozyme enzymes is released into phagosome. Enzyme hydrolyses the pathogen.
-This destroys pathogen.
-Soluble products are absorbed and used by the phagocyte.
What are lymphocytes involved in?
Specific immune response.
Where are lymphocytes made and matured?
Made in bone marrow but lymphocytes are matured in thymus gland.
What are the stages of cell-mediated response?
-Once pathogen has been engulfed and destroyed by phagocyte, antigens now positioned on cell surface. This now called an APC.
-Helpter T cells have receptors on their surface which attach to antigens on APC.
-Once attached, this activates helper t cells to divide by mitosis to replicate and make clones.
-Cloned helper T cells differentiate into different cells.
Some remain as helper T cells and activate B lymphocytes.
Some stimulate macrophages (phagocytes) to perform more phagocytosis.
Some become memory cells for shaped antigens.
Some becomes cytotoxic T cells.
What do cytotoxic T cells do?
They release a protein, called perforin, which embeds in the cell surface membrane and makes a pore so substances can enter and leave a cell.
This causes cell death.
Describe stages of B cell activation.
-Antigens in blood collide with complementary antibody on on B cell. B cell takes in antigen by endocytosis and presents it on it’s cell surface membrane.
-When this B cell collides with helpter T cell receptor this activates B cell to go through clonal expansion and differentiation.
-B cells go under mitosis to make large number of cells, they differentiate into plasma cells or memory B cells.
-Plasma cells make antibodies.
-B memory cells divide rapidly into plasma cells when reinfected with same pathogen to make large number of antibodies rapidly.
How long do plasma and memory B cells live for in your body?
Plasma- a few days
Memory B cells- Decades
What is agglutination?
Antibodies are flexible and bind to multiple antigens to clump them together.
This makes it easier for phagocytes to locate and destroy the pathogens.
How can lymphocytes distinguish between pathogens and self-cells?
Each cell has specific molecules on its surface that identify it. These molecules are usually proteins as their 3D tertiary structures enable lots of unique and identifiable shapes to be made.
What non-self cells can lymphocytes detect?
Pathogens
Cells from other organisms of the same species
abnormal cells (cancer cells)
Toxins
What are antigens?
Molecules that generate an immune response by lymphocytes when detected in the body.
They are usually proteins and are located on the surface of cells.
Explain antigen variability.
Pathogens DNA mutate quite frequently. If mutation occurs in the gene that codes for the antigen, then the shape of the antigen will change.
Any previous immunity to this pathogen is no longer effective, as all memory cells in the blood will have a memory of the old antigen shape.
What is passive immunity?
Antibodies are introduced into the body.
The pathogen does not enter the body, so plasma cells and memory cells are not made.
There is no long term immunity.
eg. antibodies passed to fetus through placenta or through breast milk to a baby.
What is active immunity?
Immunity created by your own immune system following exposure to pathogen or its antigen.
