Safe from harm: this is the prime directive for the immune system. This system in the body is not perfect, but it’s pretty good. Automatically, spontaneously, vigilantly, and mindlessly, this system monitors the body for enemies—domestic and foreign—for credible threats, expertly ignoring the innocent and relentlessly pursuing the dangerous. At least, in a perfect world.
If the immune system is so good at what it does, why is my nose running?
As stated above, it’s not perfect. We live in a much cluttered world. Any deep breath indoors is liable to take into the body dust motes of insect parts, insect waste, dirt, dead skin from others, viral particles, fungus, bacteria, and particulate pollution from cooking and smoke.1 Go outdoors and one inhales pollen, diesel pollution and other smog, dust, burn soot, a variety of microorganisms, and even burnt meteorite particles.2 But where does the immune system draw the line between friend and foe?
The thickness of that line is thin in some people, thick in others. If there is some recognition overlap confusing the immune system, it is in degrees, such that there is a range of immune reactions, from runny nose (e.g., allergic rhinitis with seasonal allergies) all the way to death (e.g., anaphylactic shock from a bee sting). Then there are others who live their entire lives without so much as a single hive or used tissue.
Below is a discussion of the immune system, but it is simplified for the purposes of an overview. Actually, there are entire textbooks that describe the enormous breadth of the immune system, and that is just of what we know so far!
What are the components of the immune system?
There are several components, making up primary defenses, secondary defenses, and so on. More accurately, there is an innate immune system, the first responders, with which we are born. The adaptive immune system, fine-tuned throughout life, is slow, taking days to fight a bacterium, so it is the innate system that covers the situation until the adaptive system can kick in.
Innate immune system
- This is the system with which everyone is born. Inflammatory proteins, antimicrobial molecules, and other first-line sentinels that work at first contact but also signal the adaptive immune system to engage. The microbiome—our normal bacterial friends with whom we co-exist—help to maintain a balance between normal bacteria and overgrowth of others.
- Mast cells release inflammatory substances against bacteria and viruses when exposed to them. They are like hand grenades, releasing (“degranulating”) molecules harmful to invaders. When mast cells overreact, they are among the “usual suspects” in allergic reactions. Mast cells release histamine which attracts more mast cells but also eosinophil white blood cells (one of the “usual suspects” in allergies. It also mobilizes the T-cell reaction of the adaptive immune system.3
Adaptive immune system
- Lymphocites, a type of white blood cell, as well as neutrophils, come in “T” and “B” varieties. (“The hounds,” see below.) With exposure to a harmful invader, the surfaces of these cells develop receptor sites that match the shapes of the intruders, then clone themselves to create armies specialized for specific invasions, armed with antibodies.
- Phagocytes—other white blood cells (leukocytes) that literally eat the enemy (neutrophils, monocytes, and macrophages). An important property of phagocytes is that when they eat the enemy, they swallow (surround and encapsulate) normal dead cells whole so that one doesn’t form an immune response to normal cells. Dead cells are “out of sight, out of mind” before any immune stimulus even begins for these. Other leukocytes include the basophils that signal the release of T-cells and B-cell antibodies (“Release the hounds!”)
- Natural killer cells. Yep, naturally born killers that attack viral infections and malignant cells.
What is an allergic reaction?
Allergic reactions are overreactions of the body’s immune system.4 Things that trigger allergic reactions are called allergens. Allergens—for example, a bee sting—will cause a local reaction (the innate immune system), but exposure to the toxin will mobilize the adaptive immune system, which prepares for the next sting and is ready to spring into action. B-cells of the adaptive immune system make a particular type of immunoglobulin, IgE, well known for provoking its allergy-caused reactions.
If one were to have an overreaction of the adaptive immune system, a second bee sting could cause anything from hives to trouble breathing, even death if an extreme reaction is launched. Most people merely get the local irritation again, but some have time bombs in their system, just waiting for the second strike. (“Fool me once…)
What are types of allergic reactions?
With the varied defenses contained within the immune system, it is logical to assume that there are many types of allergic reactions, including:
- Seasonal allergies: sneezing, stuffy or runny nose, or itchy eyes from exposure to insects, animal dander, mold, pollen, etc.
- Drug allergies: drugs are just as much an invader as cockroach waste. However, drug synthesis is focused on allowing therapeutic benefit without angering (triggering) the immune system, but this is not always successful.
- Infections, not normally thought of as allergies, nevertheless are related because the response to infection is an immune response. Typically, an allergy has calling cards with a certain type of antibody, IgE, and a certain type of white blood cell, the eosinophil. Infections generally involve IgG and IgM and the white blood cells called neutrophils and lymphocytes. The different amounts of these immunoglobulins and white blood cell types can be tallied in lab studies to help differentiate between infections and allergic reactions.
- Anaphylaxis: this is an overwhelming IgE antibody response. Also, IgG (immunoglobulin G) and mast cells can cause it as well. There is massive collapse of the cardiovascular system resulting in severe fluid shifts at the cellular level and resulting shock (severe hypotension).
Who is at risk for allergic reactions?
Two factors are recognized:
- Genetic. This is the most blameworthy.
Allergies simply run in families. Atopic dermatitis, lactose intolerance, seasonal rhinitis, asthma, and other miseries can usually have a family history rife with similar complaints. This could be either a straight inheritance of oversensitivity or even an “acquired” oversensitivity that is passed on (see epigenetics, below).
- Environmental. This is complicated.
It spans a gamut—from too much hygiene in infancy and the early years (not enough exposure to allergens to make “friends” with them) to epigenetics (genes turning on and off while living life, which is then passed on to offspring). There may be a value to toddlers rolling around in the dirt with Fido or eating mud. (Make sure it’s just mud!) Also, there is definite value to a wide assortment of diet choices. The earlier the better—the peanut industry will thank you.
How are allergies treated? How are severe reactions prevented?
If an allergy is an overreaction, then avoidance strategies (staying away from the allergen—which is the best policy in preventing severe reactions—and calming down the overreaction are the ways to treat it.
Steroids stabilize the cells that release the immunological substances that cause the trouble. In essence, the put out the fuse.
Physicians, dermatologists, and immunologists can “desensitize” an individual, exposing him or her to small amounts of the suspect allergen and then increasing the exposure until there is no more overreaction.
For treating severe reactions, it’s a matter of catching one’s own tail, usually with adrenaline (epinephrine) by injection to reverse the ongoing allergic mechanisms. Having an EpiPen around can make the difference between life and death.
Allergies and allergic reactions are overzealous immune responses, ranging from mild irritability of the innate immune system to zero-tolerance on the part of the adaptive immune system. Asthma, seasonal allergies, and drug hypersensitivity can soften over years, but can also remain as immunological baggage with which one must be saddled for an entire lifetime.
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