Download Immune response

2.2.2 Health and Disease
•Define the terms immune response, antigen and
antibody;
• Describe the primary defences against pathogens
and parasites (including skin and mucus membranes)
and outline their importance. (No details of skin
structure are required);
2.2.2 Health and Disease
•Immune response is any defense mechanism of the body that is
initiated against a perceived foreign object.
•Some primary defences against invasion are:
Skin – water proof and impervious to most types of bacterial
attack. Oil on surface of the skin is toxic to bacteria.
Mucous membranes: Trap dirt hair and bacterial particles.
This is then ejected from the body helped by cilia which waft
to aid movement.
Tears, saliva and urine: Contain chemicals toxic to bacteria.
2.2.2 Health and Disease
•Antigen: Large, complex molecule such as a protein,
long sugar molecule and glycoprotein which allows
immune system to recognise pathogens.
•Antibody: Protein molecule secreted by B
lymphocytes. Made of 4 polypeptides joined
together.
2.2.2 Health and
Disease
•
Describe, with the aid of diagrams and
photographs, the structure and mode of action of
phagocytes;
• Describe the structure and mode of action of T
lymphocytes and B lymphocytes including the
significance of cell signalling and the role of memory
cells
The immune response
• If our body’s barriers to infection are bypassed our
immune system will step in and try to fight off the
pathogen.
• There are 2 main types of cells in our immune system:
Phagocytes and lymphocytes
Phagocytes
There are two types of phagocytic white blood cells:
Neutrophils
and
macrophages
which engulf and digest foreign particles of almost any
size or type
Macrophages
• Also leave the blood
• When IN the blood called
“monocytes”
• When in liver (which they
often are in large
quantities) called “Kupffer
cells”
• Long lived, surviving after
taking in foreign particles
Break foreign particles up into their component molecules then place some
of these in their plasma membrane. Cells that behave in this way are called
“antigen-presenting cells” (APCs) This helps other cells identify invaders
Neutrophils
• 60% of white blood cells
• Short lived
• Often destroyed after
killing bacteria
• Constantly being remade
in the bone marrow
• Often leave the blood to
actively patrol parts of
the body with invaders
Phagocytosis
Pathogens are taken in by phagocytosis and fused with
lysosomes that break the bacteria up and then
removed from the cell.
Lymphocytes
There are 2 types of lymphocytes:
B Lymphocytes
and
T Lymphocytes
Which look identical but differ in their functions, both are
stimulated
by ANTIGENS and produce
ANTIBODIES (this action is SPECIFIC)
B Lymphocytes
• Develop in bone marrow
• Meets specific antigen in blood or on an APC
• Responds by dividing repeatedly to form a large number
of clones
• (1) Some will differentiate into plasma cells which rapidly
produce more antibody which is released by exocytosis
• Antibodies spread around the body and bind with
bacterial antigen, resulting in their destruction
• (2) Other cloned cells don’t secrete antibodies but
instead remain as MEMORY CELLS which persist and can
respond quickly if the same pathogen invades again
T Lymphocytes
• Spend time developing in thymus gland during childhood
(this gland disappears by teenage years)
• Only respond to their specific antigen if presented in the
plasma membrane of another cell, then replicate to make
clones
• There are different types of T lymphocytes;
Memory
cells
T helper cells divide to replicate
themselves then secretes
CYTOKINES, chemicals that
stimulate other cells to fight the
invaders. Helper cells also
stimulate killer cells
T Killer cells actually destroy
the cell they’re bound to by
secreting chemicals such as
hydrogen peroxide. These
are our main defence.