Part 2: The snapshot of immunity
So, my last post on the perception around Covid vaccines (and the basics of the immune response) seems to have generated a fair amount of interest, and consequently a number of follow-up queries. The primary topic in the messages that I received has centered around the ‘snapshot’ that I referred to: the picture (protein) that the police (immune cells) use to identify the intruder (the infectious agent). The more accurate the snapshot, the better the response.
Well, time for another long post. Grab a protein drink and read on…
We will start with the very basics. Creating and maintaining snapshots is expensive, in terms of time, nutrients and energy. Snapshots may also fade over time (means you haven’t seen the infection in a while), so the body may decide to discard them. At any point in time, it is said the body of an average middle-aged human being can differentiate between around 10 trillion different snapshots (corresponding to the various pathogens/toxins encountered through life).
Think about that for a second. That’s 1,000,000,000,000 different snapshots.
Let’s bring this number down to 1000, just to make things easy to follow. We’ll also simplify things by assuming that all the cells that actually belong to the body look the same, so you either look like you belong or you don’t.
Here’s where the term ‘self vs non-self’ makes its appearance. We now have 1 ‘self’ snapshot (belongs to the body, leave it alone) and 1000 non-self (doesn’t belong and should be eliminated).
Imagine the plight of the foot patrol officer scouring the neighbourhood. He/she would have to carry a book of 1001 photographs. Each time a new person is encountered, you would need to check all 1001. If the person matches any of the non-self, you nab him (or destroy the house he’s in). If the person matches the self, you leave him (or the house he’s in) be. Imagine the energy and resources this would warrant. Mind you, there are thousands of such patrol officers scouring all the streets (millions of cells all through the bloodstream).
Evolution solved this in a very clever and efficient manner. The officer carries a book of just five snapshots. Of these, 1 is self, and 4 are the top repeat offenders (bacteria/fungi/infectious micro organisms that have been seen time and again during evolution). Decisions can now be taken swiftly and effectively. You protect the self, kill the non self.
But what if the person doesn’t match any of the 5? Well, you nab him anyways, because you don’t know if he’s good or bad. You then take him to the precinct (lymph nodes) where the book of 1001 is maintained. If you find a match with any of the 1000 non-self, specialised squad cars (B cells and antibodies) and SWAT teams (T cells) are immediately deployed, all carrying just that ONE snapshot of interest. Chemicals are deployed at the original site of the infection, so the B and T cells can home into the targeted region where the suspect was first picked up, so all the intruders of that type can be flushed out and eliminated (instead of going endlessly and aimlessly all over the body). Swift, efficient, life-saving. Once the job is done, the deployed B/T cells are scavenged for nutrients (and use for other body functions). Why waste energy, after all?
We now come to the million-dollar question. What if the suspect first picked up ‘didn’t’ match any of the 1001? Well, we now need to create a new snapshot. Cells don’t have cameras, so they instead try to recreate the shape of new suspect protein (like a sketch artist building a likeliness). Each time a sketch is created, it is compared to the new intruder AND to the self. If it matches the self, it is immediately destroyed. If it matches the intruder poorly, a new sketch is created. And so on, until after millions of copies and checks, the perfect match is found and added to the book to create 1002 entries (1001 non self and 1 self).
Please read the previous paragraph AGAIN! Before you deploy killer cells, you better have the EXACT (or closest) match to the intruder and the least match to self, else you are looking at the possibility of severe collateral damage. Auto-immune conditions like rheumatoid arthritis fall under this category, where the body attacks its own self, causing swollen joints all kinds of inflammatory issues.
Hopefully, you now understand why it takes 1-2 weeks for a response whenever a completely new infectious agent is encountered, while it is a lot more swift once the snapshot is already in the book. Hopefully, you also understand why it is energy and protein intensive. I gave you an example with a count of 1000, scale that up to a trillion, and you should start to see the enormity of the task at hand.
We will visit vaccines in a subsequent post, but I believe the challenges should have started becoming clear. You want to introduce something into the body that ‘looks’ like the virus, but doesn’t cause the nasty symptoms but still causes a generation of the immune response and finally, an addition of the snapshot to the library.
Regardless, the mantra remains the same. Give your body the nutrients it needs and don’t get in its way (avoid packaged/processed foods that typically contain no useful nutrients and instead trigger inflammation, stress and new detoxification problems for your liver to deal with).
Until next time…..
For the technically inclined (and who may wish to delve deeper into literature), I am listing a few terms here:
The patrol officers carrying the 5 snapshots are the innate immune cells (macrophages, neutrophils, dendritic cells)
The sketch artist drawing millions of sketches are your B cells generating millions of antibodies (before the right one is identified and activated)
The cells regulating the activity at the precinct are helper T cells (also known as CD4 cells)
The cytotoxic (killer) T cells are known as CD8 cells