Infection and the nonspecific immune response

How do pathogens enter the body?

• through wounds in the skin

• through the digestive system in food or drink

• through the respiratory system (inhaled)

• through mucosal surfaces (nose, mouth and genitals

What are the barriers used by the body to prevent infection?

• stomach acid

• skin acts as a physical barrier to pathogen

• gut and skin flora

• lysozymes

What would happen if you damage your skin?

• pathogens on the surface can enter your bloodstream

• blood clots at the area of damage to prevent other pathogens from entering

• however some may enter before the clot forms

How does stomach acid prevent infection?

will kill most pathogens (however some will make it through and pass into the intestines and enter cells of the gut wall)

How does gut and skin flora prevent infection?

• the intestines and skin are lined with billions of harmless microorganisms

• they compete with the dangerous pathogens for nutrients and space

• this limits the number of pathogens living in the gut and skin

• make infection difficult

How can lysozymes prevent infection?

• mucosal surfaces produce secretions like tears saliva and mucus

• they all contain lysozyme enzymes

• lysozymes kill bacteria and damage cell walls

• bacterial cells will burst (cell lysis)

How is an immune response triggered?

• pathogens have antigens on their surface

• the antigens are recognised as foreign

• activates immune system

• can be either specific and non specific

Which immune response occurs first?

nonspecific

What happens in a non specific immune response?

• Inflammation at the site of infection

• Production of antiviral proteins (interferons)

• Phagocytosis and Lysozyme action

Inflammation at site of infection

• Immune system recognises the pathogens as foreign

• Release molecules that trigger inflammation

• Causes vasodilation around the site of infection

• Increasing blood flow to the area

• Molecules increase the permeability of blood vessels

• Increased blood flow brings the immune system cells to the site of infection

• These move out of the blood vessels into the infected tissue

• The immune system cells can start to destroy the pathogen

Production of antiviral proteins called interferons

• When cells are infected with viruses they produce proteins called interferons

• Interferons prevent spread of virus to uninflected cells

• They prevent viral replication - inhibit production of viral proteins

• They activate cells in the specific immune response to kill the infected cells

• They activate other mechanisms of the non specific immune response e.g. promote inflammation to bring immune system cells to site of infection

Phagocytosis and Lysozyme action

• phagocyte is a white blood cell that engulfs pathogens

• found in the blood and tissues

• phagocyte recognises the antigens on pathogen

• phagocyte engulfs the pathogen

• pathogen is now in a phagocytise vacuole in the cytoplasm of the phagocyte

• a lysosome (contains digestive enzymes like lysozymes) fuses with the vacuole with the pathogen

• the enzymes break down the pathogen

• (MHC protein will bind to the antigen fragment and present the antigen on the different

• the phagocyte presents the pathogens antigens on its surface to activate other immune system cells

• this is an APC