The immune system in a nutshell

The immune system in a nutshell

Imagine you have a $3M house smack in the middle of nowhere. Bad stuff goes on outside your perimeter. A tall concrete fence topped with barbed wire surrounds your property; strategically placed cameras provide 360 degree views of the periphery. The gate that can only be opened electronically.

All of the open yard area is equipped with motion detectors. The house itself is protected by a security system that sounds an impressive alarm when anyone or anything attempts to enter a door or a window.

A 24 hour security detail is camped out on your roof. They maintain visual patrol plus monitor the cameras and motion alarms. At any sign of trouble the guards release several mean Doberman Pinschers and prepare, if necessary, to call in the national guard.

You live happily within the confines of your house, confident you are protected from bad stuff happening outside.

The innate immune system

Consider what I have just described as your “innate” immune system. That is the first of two parts of your complete immune system.

The innate system is on patrol at all times, getting signals from your various cells in your body when something shows up that doesn’t belong. Just like the Doberman’s mentioned above, the innate system doesn’t know exactly who the invader is but it responds immediately, doing its best to kill anything dangerous before it gets into your cells and starts an infection.

The adaptive immune system

While the innate system just blindly moves out, the adaptive does just what you might think. It assesses and adapts to the situation. The innate system alerts the adaptive immune system to gear up in case the innate response isn’t enough.

Look at it this way. Somehow the intruder has evaded the dogs. The security detail now calls in the national guard. There are two national guard troops called T-cells and B cells. Each has their own specialty. However they cooperate and coordinate with each other. This is your adaptive immune system.

The adaptive system, the T-cells and B-cells, both take a few days to respond. In the meantime the security detail on the roof is shooting and the dogs are still hunting. Why so long?

All cells are made of protein. T-cells and B-cells are looking for the proteins in invaders which are different from human proteins. The presence of foreign proteins tell the immune system which cells to attack. Attacks on human proteins are bad.

There are an infinite number of protein possibilities and identifying the right ones will take some time. The T and B cells’ job is to fight an active infection that the innate system fails to prevent. They are your last source of defense and they need to get it right.

Invaders could be a lot of things that don’t belong. Some could be one of 208 viruses, 538 bacteria, 317 fungi, 287 worms, and 57 parasites. At least that was the number the last time I looked.

Baby T-cells and B-cells are being continuously created in bone marrow and dumped into circulation. whether there is an invader or not. When they are signaled to activate by the innate system, they begin looking for mismatched proteins.

I won’t explain how the adaptive immune system works in depth because it would take too long and be too complicated. This link provides the simplest explanation I could find.

However, here are links from the Kahn Academy that provide excellent detail. — Innate immune system and adaptive immune system. This link just focuses on differences between T-cells and B-cells. And if you really want to work hard at it, this youtube video gets deep into the detailed operation of the immune system.

For our purposes here, suffice to say the adapted T-cells move in force through your blood and lymph system checking every one of your cells for mismatches and take steps to destroy infected cells. There are several different kind of T-cells that employ different strategies.

Once matured, the B-cells, on the other hand, arrive with antibodies attached. Once again the mismatched protein has to be found so that the antibody can attach to it. A protein with antibodies attached is thus marked for destruction by the T-Cells.

Once a B-cell encounters an invader that matches its antibody, it divides and replicates into two forms. One type becomes a memory cell, the other circulates in the body secreting the antibodies.

Replicated memory cells are stored in bone marrow for future use. This means should this particular invader, whatever it is, show up again on another day, the response to that invader can happen much faster. Vaccines are antibodies “on ready”.

Next time the same somebody manages to get over your fence and approaches your house, the national guard unit called memory is standing by to attack without delay. However, if the intruder is different (say the flu as opposed to COVID-19) that particular memory cell won’t respond.

When the immune system isn’t tied up responding to invaders that might kill you it also repairs wounds, disposes of dead cells, and removes abnormal cells (such as those that can become cancer). Abnormal cells don’t belong either.

Why the Immune System might not work correctly

When it comes to the security system for your house, stuff can go wrong. Maybe the quality of the concrete was poor, deteriorates and develops holes. The barbed wire was purchased on sale, rusts and breaks before its time. A power failure takes down the motion detectors. The dogs don’t get fed, the national guard troops don’t have ammunition or the ammunition is inadequate to the job.

I have described what will happen in a person whose system is in good working order. On occasion some portion of a person’s immune system can be faulty due to genetics. Plus some invaders are worse than others.

For example, the HIV virus typically infects T-cells themselves. Remember that the T-cells are supposed to be the killers in the immune system. An infected T-cell can’t do its job. Plus the HIV virus mutates at warp speed. This helps explain why, after all these years, a vaccine has not been identified, thus requiring instead drugs that will stop the virus from replicating.

On occasion the system seems to get confused, thinking that some human protein (called self) is foreign (not self) and attacks. This is a bit like the national guard shooting the dogs instead of the intruder. This results in an autoimmune condition.

That brings us to the “underlying conditions” (including autoimmune conditions) that challenge the immune system all on their own. These belong to unhealthy people and are frequently present in older folks. Obesity, diabetes, cardiovascular disease, lung conditions, the list goes on.

Finally, nutritional requirements may not be met. Every single cell in your body, including immune cells, has a requirement for the right vitamins and minerals, proteins and healthy fats. The typical American diet fails rather badly in providing for these requirements. “Underlying conditions” most often occur for the same reason.

When it comes to fighting off infection, being sick is not a good thing. Being old and sick is worse still.


Covid-19 is a new virus not seen before. None the less so far we know that the innate immune system seems to handle Covid-19 for a large percentage of younger people. We know that 70-80% of those who die are old folks with underlying health conditions. Sometimes the COVID-19 infection is the straw that broke the camel’s back. We also know that there have been miraculous survivals in old folks without underlying health conditions. Health seems to be the key.

Pat Smith is the author of “It’s All about the Food,” a book that guides nutritious food choices as the way to avoid illness and maintain a healthy weight. Proceeds from her book benefit the Montgomery County Food Pantry. Her website is She can be contacted at, 870-490-1836. Her Facebook page is