Why do we take antibiotics if our immune system already produces them? Is it because our body doesnt make enough or the specific complementary antibody to fit with the antigen?
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Since people and animals routinely get sick, it is obvious that our immune system (which includes but isn't limited to antibodies) doesn't always protect against pathogens. There are many reasons for this, far too many to summarize here, but one common reason is that it takes several days for the adaptive part of the immune system (which includes antibodies, among other things) to gear up and control an infection. Therefore, early treatment with antibiotics can help limit an infection before the immune system is fully engaged.
Pathogenic bacteria are often resistant to immunity in many ways as well; that's one of the adaptations that makes them pathogenic. That means that even later in an infection, antibiotics can supplement the immune response and help eliminate bacteria. Note that many antibiotics require a functional immune system to be completely effective.
We take antibiotics when our own immune system is insufficient to control infections. We do make antibiotics as localized defence systems
Defensins and cathelicidins belong to antimicrobial peptides (AMP), called also the natural antibiotics. They are found in Prokaryotes and Eukaryotes, also are synthesized in plants. These molecules were described in bacteria, invertebrates, vertebrates, also in mammals including humans.
But clearly these can be overwhelmed by bacteria resistant to their action, or by overwhelming rates of reproduction of invading bacteria
Our mammalian physiology has further evolved the innate immune system, and the adaptive immune system to cope with invasions that bypass these simple non-adaptive molecular defenses.
I assume from your question (and your pseudonym) that you are confused by terminology. Our adaptive immune system does not make antibiotics, it makes antibodies. Antibiotics are small molecules that interfere with bacterial metabolism. Antibodies are proteins that recognise foreign macromolecules. (You could regard both as “anti-bacterials” — perhaps this is what you were thinking of — but the immune system is not restricted to recognizing bacteria.)
We take antibiotics when we have an infection from bacteria that have evaded the immune system.