The first lines of defences are the barriers on the surface that protect the body from pathogens. This includes skin and mucous membranes. The first line of defence helps because if the pathogens cannot enter our bodies, they can not cause diseases.
Innate Immune System
The second line of defence is a cellular and molecular response to the innate immune system. This defence responds the same way with every infection of the pathogens. In this line of defence, phagocytic leukocytes travel to infection areas and overtake foreign bodies.
Acquired Immune System
The third line of defence is against infection. This line is the lymphocytes that make antibodies to stop antigenic fragments. Each B cell produces a specific antibody. The body has many different B cells that are capable of finding distinct antigens. The T cells help control what the B cell does. They both remember a particular pathogen so it knows what to do if that type of pathogen enters the body again.
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The innate immune system is the system that we are born with. The 2 stages are physical barriers and defense mechanisms, which are the 1st and 2nd line of defenses. Some examples of physical barriers are skin and mucus. Some defense mechanisms include secretions.
The acquired immune system is the system that develops inside of our bodies as we grow up. The stage that is considered a part of it is the 3rd line of defence. The third line of defence is against the infections that enter our bodies. These infections enter our bodies as we grow up and we are not born with it. This line of defence develops when certain pathogens arrive.