Transcript The Immune System

The Immune System
Non-Specific Immunity
What You Should Know
• The human body has the capacity to protect itself against
pathogens, some toxins and cancer cells through the immune
system.
• Non-specific defences include physical defence as the epithelial
cells form a physical barrier and chemical defences – chemicals
are produced and secreted against infection.
• Inflammatory response includes the release of histamine by
mast cells causing vasodilation and increased capillary
permeability.
• The increased blood flow and secretion of cytokines leads to an
accumulation of phagocytes and the delivery of antimicrobial
proteins and clotting elements to the site of infection.
• Phagocytes and NK (natural killer) cells release cytokines
which stimulate the specific immune response.
• Phagocytes recognise surface antigen molecules on pathogens
and destroy them by phagocytosis.
• NK cells induce the pathogen to produce self-destructive
enzymes in apoptosis.
Non-specific Cellular Defence
• The body has an immune system for defence
against
– pathogens
– some toxins produced by living things
– cancer cells
• Immunity is the ability of the body to
– resist infection by a pathogen
– or to destroy the pathogen if it invades the
body
First Line Defence-Non Specific
• Barriers defence
– The skin is composed
of layers of epithelial
cells which provide a
physical barrier
against bacteria and
viruses
– Mucus membranes
that line the digestive
and respiratory tracts
are also composed of
epithelial cells
• Chemical defence
- Secretions from the skin’s sweat glands and
sebaceous glands keep the pH of the skin too low
for many organisms
- Secretions such as tears and saliva contain
lysozyme which digests bacterial cell walls killing
them
- Cells in mucus membranes secrete
mucus which traps microorganisms
- Ciliated cells in the trachea sweep
mucus and trapped microbes up and
away from the lungs
– Acid secreted by the epithelial cells
lining the stomach destroys many of the
microbes which have been swallowed
bacteria (yellow) sticking to the
mucus (blue) on the hair-like cilia
Inflammatory Response
• Prevents
– spread of injurious agents to adjacent tissues
– disposes of pathogens and dead tissue cells
– promotes tissue repair
Mast Cells and Histamine
• Histamine –
– released from mast cells
and promotes
vasodilation of local
arterioles and increased
permeability of local
capillaries
• Signs: redness, pain, heat
and swelling
• Increased blood flow and
permeability of capillary
walls enhances the
migration of phagocytes to
the damaged area
Cytokines
•Cytokines are cell signalling proteins released by
phagocytes and natural killer cells when in contact with a
pathogen
•They are important in both non specific and specific
immunity
•Secreted from white blood cells at the site of injury
•The increased blood flow and secretion of cytokines
leads to
o an accumulation of phagocytes which carry out
phagocytosis
o the delivery of antimicrobial proteins and clotting
elements to the site of infection
Phagocytes
• Phagocytes also release
cytokines which stimulate
the specific immune
response by activating
lymphocytes
• Phagocytes recognise
surface antigen molecules
on the pathogens and
destroy them by
phagocytosis
Natural Killer Cells
• Natural killer cells also
release cytokines which
stimulate the specific
immune response by
activating lymphocytes
• NK cells attack virus
infected and cancerous
cells
• NK cells release proteins
that cause the cell to
produce self-destructive
enzymes resulting in cell
death by apoptosis