Define 1st, 2nd, 3rd, line of defense.

First line: mechanical, chemical and microbial
Second line: internal/non-specific, involves the immune system
Third line: internal/specific

Not sure exactly what kind of answer you are looking for so i hope this able to be a effective listener and also being  a good conversationalist. and most of all just being there when someone needs you.i hope this .

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