The Beautiful Immune System Lesson 2: Protective Immunity

When our bodies become sick with a virus, bacteria, fungi, parasite, etc., our adaptive immune system, the one that “remembers” microbes, not only fights off the microbe but creates protective immunity against it.

Protective immunity is the body’s ability to resist a certain disease. The body’s source of protective immunity against microbes comes from the antibodies created by B cells, as well as the memories stored in the body’s specialized lymphocytes (B and T cells). By “specialized”, I mean they hold a special memory of the particular microbe the protective immunity is against.

Before the lymphocytes have seen a particular microbe are said to be naive, or immunologically inexperienced to that microbe. Once the body has been exposed to the microbe, killed, and remembered it, you would be said to be “immune”to that microbe. Therefore, if the microbe should enter the body again, circulating antibodies would readily identify it and it would be targeted by the lymphocytes for attack.

When the body is forced to make this type of response to a natural microbe, we call this active immunity, because the immune system plays an active role in responding to a microbe.

Vaccines can force the body to make a response to weakened, killed, or bits and pieces of microbes in order to create protective immunity. Therefore, vaccines also induce an active form of protective immunity.

Protective immunity can also be given passively. In this case, the body does not need to actively make a response to a microbe. This happens in two particular cases.

Antibodies are transferred from mother to baby via the placenta or through breast milk. This gives the baby passive immunity–maternal antibodies that the baby’s body did not make itself–to many diseases for a short period of time to protect the baby in its first few months.

Immunizations are the second form of passive immunity. Now, I said “immunizations” not “vaccines”. “Vaccines” are, as stated above, weakened, killed, or bits and pieces of microbes injected into the body for the body to make a protective active response to. “Immunizations” are injections of serum containing pre-made antibodies or pre-made lymphocytes with specificity to a particular disease. “Immunizations” are for making a person instantly immune to a disease. There is a difference!

Immunizations are particularly important if a person needs to become immune to a disease right away and does not have time to allow the body to make a proper immune response.

An example:

Let’s say you get the live DTaP vaccine. The “T” refers to tetanus, here, and because the vaccine is live, you know that your body will be making a response to a live, but weakened form of the tetanus bacteria. Good for you if you got this vaccine; you’re covered for 10 years! Should something happen, like you fall on a rusty nail and get a nasty cut, you don’t really need to worry so much about contracting the tetanus bacterium and falling very, very ill.

However, if you’ve never had this vaccine and you clumsily fall into say, a rusty barbed wire on a farm near lots of animals (double threat, but I will explain more about tetanus in a later post), you should be a little worried about tetanus. But, just because you haven’t been vaccinated doesn’t mean there is no hope. Some diseases, NOT ALL, have licensed immunoglobulin (antibody) immunizations. Should you need it, and in this case you may, you can be given antibodies to tetanus right away to help fight off the disease. And you can thank your lucky stars.

Resources:

  1. Abbas, Abul K., Andrew H. Lichtman, and Shiv Pillai. Cellular and Molecular Immunology. Philadelphia: Saunders Elsevier, Inc., 2010.
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