Organisms must constantly protect themselves from harm caused by pathogens like viruses and bacteria. The immune system delivers this protection via numerous pathways.
The immune response is broken down into innate immunity, which an organism is born with, and adaptive immunity, which an organism acquires following disease exposure.
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Immunity is defined as an organism’s ability to protect itself from a pathogen or toxin.
What is innate immunity?
Innate immunity, also known as genetic or natural immunity, is immunity that one is born with. This type of immunity is written in one’s genes, offering lifelong protection. The innate immune response is fast-acting and non-specific, meaning it does not respond differently based on the specific virus or bacteria that it detects.
The innate immune system encompasses physical barriers and chemical and cellular defenses.
- Physical barriers protect the body from invasion. These include things like the skin and eyelashes.
- Chemical barriers are defense mechanisms that can destroy harmful agent. Examples include tears, mucous, and stomach acid.
- Cellular defenses of the innate immune response are non-specific. These cellular defenses identify pathogens and substances that are potentially dangerous and takes steps to neutralize or destroy them.
Another way to categorize the components of the innate response is by external defenses, like skin and tears, and internal defenses, like stomach acid and cellular defenses. External defenses provide the first line of defense against pathogens while internal defenses offer the second line of defense.
What is adaptive immunity?
Adaptive immunity is an organism’s acquired immunity to a specific pathogen. As such, it’s also referred to as acquired immunity.
Adaptive immunity is not immediate, nor does it always last throughout an organism’s entire lifespan, although it can.
The adaptive immune response is marked by clonal expansion of T and B lymphocytes, releasing many antibody copies to neutralize or destroy their target antigen.
The first time the body encounters a novel disease agent its response is known as the primary immune response. When B lymphocytes, or B cells, encounter a novel antigen, they create antibodies specific to the antigen designed to destroy or neutralize it.
Simultaneously, B cells create memory cells, which are a type of B cell that survives for decades and can detect the pathogen during subsequent exposure.
It takes the body time to create antigen-specific antibodies the first time, and therefore this response takes longer than subsequent responses.
If an organism encounters the same pathogen a second time, the immune system’s response will be faster and more robust than the primary immune response. This increased speed is thanks to memory cells.
The above description of adaptive immunity describes active immunity, which is the immunity that occurs following pathogen exposure.
Another type of adaptive immunity is passive immunity. Passive immunity occurs when an organism receives external antibodies that protect against disease.
This protection can occur from mother to baby through the placenta or via breast milk, or by injection to defend against a specific disease.
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