Passive Immunity: Definition and Example

Passive Immunity Definition

A passive immunity is a resistance to a disease or toxin where the resistance was gained without the immune system producing antibodies. Any foreign body, whether it be a virus or a toxin, is likely to harm an organism’s cells. To preclude this outcome, organisms have developed both passive and active immunities to combat everyday threats. Unlike active immunities, passive immunities are present from birth.

A passive immunity can stop a malicious foreign body in various ways. It can provide a barrier that prevents harmful substances from gaining access to the organism, or it can be an untrained cell that attacks invaders directly. Antibodies can also be passed from one organism to another. This can happen in many natural and artificial ways. In babies, a passive immunity is given in the form of antibodies from the mother to the baby via the umbilical cord. The baby, having a weak and newly developing immune system, requires antibodies from the mother to fend off infections until the immune system is strong enough to provide an active immunity to the same diseases.

A passive immunity can come in many forms, from the barriers that separate the inside of an organism from the outside, to the further divisions that separate the blood stream from critical areas, including the brain. Still other methods of passive immunity, including genetic immunities, can be used by organisms as simple as bacteria to provide immunity to antibiotics and other chemical threats.

Examples of Passive Immunity

Skin as a Passive Immunity

A fundamental form of passive immunity in most animals is the skin. The skin is an organ made up of many layers of flattened cells. These epidermal cells form bonds between each other, and make an almost impenetrable surface. In fact, it is very unlikely that a virus or bacteria could ever make it through a section of healthy, intact skin. The problem is that viruses, bacteria, and many toxins are very small. It only takes a microscopic tear of the skin to allow millions of viruses and bacteria through. In the case of a passive immunity failure such as this, the active immunities must be produced to combat the reproduction of viruses and bacteria and the spread of toxins.

While the skin may have its downsides, it is indispensable in protecting your body from the constant bombardment of environmental dangers it is subjected to every day. Without your skin, toxins and disease could be absorbed directly from the air, water, and soil you touch. Just by separating your internal cells from these dangers, a barrier is established, providing one passive immunity for a variety of different potentially harmful foreign bodies.

However, when a large amount of toxin gets through your skin, you could be in trouble. Passive immunity is meant to block a disease or toxin before it enters your system, and active immunity is able to develop a resistance to a disease after an initial infection. If a large amount of toxin is able to get into your body past your passive immunity, how can you survive?

Antivenom as a Passive Immunity

If you were bitten by a rattlesnake, there would be a chance you could be injected with the snake’s venom. Rattlesnake venom is hemotoxic, meaning it destroys your tissues and doesn’t allow your blood to clot, causing you to bleed out. Given enough exposure to small amounts of rattlesnake venom, your body would gain the ability to produce antibodies, and you would eventually be able to survive small doses of the venom. However, in a typical rattlesnake bite, large amounts of venom are injected into the wound.

In this case, your best hope for survival would be the administration of an anti-venom. These serums contain a high number of venom antibodies, or proteins, that are able to bind to the venom, removing it from the bloodstream and tissues. In this way, the high load of venom delivered to your system can be dealt with by a shot or series of shots. Unfortunately, antivenoms are extremely expensive to produce because the antibodies are usually created in live animals and collected for use in humans.

Passive Immunity in Bacteria

Some bacteria have been shown to be able to incorporate foreign DNA into their own systems. In doing so, they can often gain an advantage over other bacteria, and thus reproduce more. One threat to bacteria is antibiotics. Antibiotics work in different ways to destroy bacterial DNA or deprive bacteria of a food source.

If one bacteria can produce a mutation that counteracts the antibiotic, it will be able to reproduce many times. These bacteria, as they die, leave remnants of the DNA that allowed them to survive. Other bacteria are sometimes able to incorporate these segments of DNA into their DNA, providing them with the ability to survive the antibiotic. Thus, they are given a new passive immunity to the drug, in much the same way a baby would receive immunity to a disease.

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