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HS bio refresh pt 2-- let's keep going! The immune system.

Let's keep going! Last blog post we reviewed viruses and herd immunity. Let's brush up on our general knowledge of the immune system.

Ok. Let's go back a bit. Remember when you hung out for 9-10 months in mommy's warm belly and then you finally got to join the rest of us on planet earth

only to find out that there were germs and diseases everywhere that wanted to kill you. And you had to figure out how to stay alive pretty darn quickly? Well, here's your chance to say: "Thank you immune system".

The immune system is a large, complex system that works to protect you from foreign threats that want to cause illness, infection, or disease. The immune system is essentially your very own military defense system. There are two main layers of the immune system. The first layer of defense is the innate immunity and the second is the acquired immunity.


Innate immunity.

Let's explain immunity using a simple cold virus as an example.

Innate immunity refers to the part of the defense system with which you were born. It's pretty generic. Everyone has the same components of innate immunity. It refers to things like: skin that protects you from germs, nose hairs that keep debris out of the airways, eyelashes that keep things out of your eyeballs, mucous membranes that act as a physical barrier for the organs beneath them. It also refers to things like the acid in the stomach that make it hard for some bacteria to survive or enzymes in tears and saliva that do the same, or the cough reflex that attempts to keep you from inhaling foreign debris into your lungs. The innate immunity also refers to special immune system cells and proteins that are triggered if germs get past the skin and mucous membranes. This is sometimes referred to as the second line of defense behind the physical barriers of skin, hair, mucosa, saliva, etc. This second line of defense includes things like your white blood cells (neutrophils, macrophages, lymphocytes), interleukins, and cytokines (*we'll get back to cytokines later when we talk about COVID-19*). This is a rapid inflammatory response to a foreign pathogen, an enemy, an invader, an antigen, a bacteria, a virus, a parasite... you get the point. [By the way, it's during this rapid inflammatory response that you usually get symptoms like fevers]. Ok. So let's stop here for a second. Let's use a common cold virus as an example.

An enemy cold virus attacks you. Your innate immune system's first line of defense is the skin, mucus, little nose hairs, cough reflex. HANDWASHING. All right. Let's say your military is a little weak on the front line and the enemy cold virus gets past that first echelon. Here we go. Rally your innate immune system's second line of defense: the troops-- the white blood cells, the interleukins, the cytokines. OPERATION INFLAMMATION! This is when you "get sick". You feel "yucky", "under the weather", "flu-like", "viral-y", "I'm coming down with something". You've said those things right? That's OPERATION INFLAMMATION. That's the part of the immune system that kicks in when your defense is trying to attack a foreign pathogen. [**by the way, bonus lesson. This is why an antibiotic like a Z-pack, isn't always the magic pill for when you feel like you're coming down with something. Operation inflammation occurs for lots of reasons, not just bacteria. An antibiotic is a medicine that works only on one specific foreign pathogen: bacteria (not viruses, not parasites, etc.) So just remember that the next time you ask your doctor for a Z-pack because you feel like you have a cold. A cold is a virus, not a bacteria. #science].


Acquired Immunity

WHAT IF your military defense is really crappy. What if that little foreign pathogen makes it past your first line of defense AND past your second line of defense? That little foreign pathogen really, really wants to inflict harm. It really wants to cause disease. Well, good thing for you, you have acquired immunity!

As a baby, you had acquired immunity from the get-go in the form of passive immunity for at least a very short period of time. You received already-formed antibodies to certain diseases from mom through the placenta while you were warm and snug in the womb. You also received some already-formed antibodies through breast-milk. These antibodies were able to get you through the transition period from the safety of the womb to the war-zone of the outside world. But now you have to make your own antibodies and there are a few ways to do it.

BUT FIRST. What are antibodies? Big buzzword-- important to understand. Also called immunoglobulins. Antibodies are proteins/molecules/things that are produced by specific cells in your body in reaction to those foreign pathogens (also called antigens) we talked about above. These antibodies are actually produced during OPERATION INFLAMMATION! And once you've made the antibodies to a specific antigen, it's in the memory books. So, if your military defense ever gets hit with that same foreign pathogen/antigen again, the memory cells of your immune system immediately make those specific antibodies again. These antibodies then connect with the antigen and mark it for destruction/termination/death. Fool me once, shame on you. Fool me twice, shame on me.

The other way to get antibodies is through vaccinations/immunizations. Traditionally, vaccinations confer immunity by exposing a person to a weakened version of the antigen or a part of the antigen and that creates the same sort of response. That immune system then learns how to produce antibodies to that antigen and puts that information into the memory bank for future use. We will go way more into detail about vaccinations in the next post.

So let's look at an example about this third layer of defense-- acquired immunity. Let's take the Measles virus. Measles is a disease that spreads through the air by respiratory droplets produced from coughing or sneezing. In children under 5 years old, adults older than 20 years old, pregnant women, and immunocompromised patients, measles can have serious consequences including pneumonia, encephalitis, and death. In the 1920s, the death rate for measles pneumonia was 30%. Measles is highly contagious, and in 1980 2.6 million people died from Measles related complications. By 2014, global Measles vaccination programs had reduced the number of deaths from Measles to 73,000.

So now we have reviewed the basic science behind viruses, herd immunity, and now the immune system. Hopefully this helps when we talk about our last topic: vaccinations. Again, this is all meant to keep everyone in the same conversation, using the same language, and having informed and intelligent discourse about the weighty topics that are no doubt at the center of everyone's dinner conversations and zoom watercooler talks.

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