Why are we able to develop lifelong immunity to some infectious diseases like measles but not others like syphilis, gonorrhea, or throat infections/strep throat?

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Does our immune system not work with STDs? I am learning about our immune system and how our antibodies work. I don’t understand what happens in which we are able to get re-infected with certain infectious disease if we should have immunity. Im guessing our immune system just doesn’t work properly against these infections?

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There are big swaths of this we don’t understand and are still studying.

But one thing that affects it is how our body decides to respond. There are organs your body considers very important and if it detects infection there it will mount a very strong response. But it turns out your upper respiratory system isn’t considered a big deal by your body, so it responds to infections there with a weaker immune response. (This may be because your nose/throat is a first line of defense against stuff getting into the lungs, so it’s constantly being exposed to bad junk and if your body reacted strongly to every incoming threat you’d be exhausted. Or be a person suffering from allergies.)

That explains why flus and throat infections tend to take hold consistently. Our body sends in the B-team at first and waits until it realizes things are bad to mount a larger-scale response. This is a big part of how COVID gets its foot in our doors!

Some viruses mutate quickly. That means even if we did see it before and make antibodies for it, the new mutations might “look” differently enough our immune systems don’t recognize it. One of the few breaks we got from COVID is the protein we target with vaccinations is crucial to how COVID infects people, so it’s very unlikely COVID can mutate in a way that fully evades vaccines AND still be able to infect us. That’s why despite new variants, the vaccines are still pretty effective at giving our immune system a head start.

But we still get sick, what gives?

Reproduction speed. Some viruses (and some mutations) replicate FAST. If they can reproduce faster than our immune system can make antibody cells, they’ll overwhelm us. That’s why Omicron seems to “evade” the vaccine. Our immune system can detect Omicron just fine, but our body sees a viral infection in our upper respiratory system and doesn’t mount a very strong response. Then Omicron reproduces like crazy and by the time our body knows there’s a problem we’re already “behind” and the virus can move to other organs.

So we’re the worst at handling diseases that mutate a lot, reproduce quickly, and target “unimportant” parts of the body. STDs usually qualify here because despite reproduction being a big goal for biological organisms, we can still live a quality life without those organs so they’re treated as low priority by many survival systems.

You’re mostly talking about the difference between viruses and bacteria, which drives how our immune system has to respond.

Bacteria, which cause things like syphilis or gonorrhea or strep, are independently alive entities. As soon as they get into a part of our bodies they like, they start to eat and multiply. Your immune system has to kill them. Every time. They don’t like being killed and fight back (hence the existance of antibiotic resistance). You can keep getting re-infected as many times as the bacteria can get in you. It takes time for your body to see/recognize the infection and respond.

Viruses, on the other hand, use our own cells to reproduce. If they can’t get into our cells they can’t reproduce and we can’t get infected. Your body doesn’t kill viruses in the same way it kills bacteria, your immune system develops antibodies matched to a particular virus and, once it figures that out, that binds to the virus and inactivates it. Once that antibody is in your system it’ll bind to any matching virus that shows up…once you’ve had that first infection, your body can kill the virus very easily/quickly if it ever shows up again.

The short answer is : it has to do with your memory B cells and memory T cells, probably

The long answer : whenever our immune system comes in contact with a pathogen (disease causing micro-organism), neutrophils and lymphocytes ( among other WBCs) come into action and depending on the type of pathogen (bacteria vs virus) different cells come into play.

Neutrophils are fast acting and ‘eat’ (phagocytose) the foreign organism quickly and without any specificity IF THE IMMUNE SYSTEM IS ABLE TO DETECT IT EARLY( will come back to this part later) —— so it is called innate immunity.

Lymphocytes (both B and T) forms what we call active/adaptive immunity. If exposed to a very specific pathogen (or a part of it/its product called an antigen) they form antibodies which attack the said pathogen. Now the thing about these lymphocytes, when exposed to an antigen in a sufficient amount (by natural infection or vaccination) a small portion of them instead of forming antibody cells, form what we call memory cells which remembers that specific antigen/pathogen and if encounters it again produces a MASSIVE response that the person won’t even feel a little sick.

It just so happens that against measles, mumps and certain viruses these lymphocytes have a tendency to form more memory cells as compared to infections with bacteria like syphilis, gonorrhea and strep. Now why these memory cells choose to form memory cells for some pathogens and not others comes down to genetics and the individual’s physiology.

The thing is and this is where speculation comes in ,bacterial infections (syphilis, strep, etc) don’t really need these energy expensive memory cells because they are easy to detect and kill because they are living cells with easily detectable biological processes and life cycle and the way they cause the disease, so it’s a lot easier to just attack them randomly with neutrophils and hence the immunity is short lasting and re-infection with the same strain might occur and different bacteria have some similarities in their structure so fast, non-specific approach works.

Viruses on the other hand are non-living until they infect a host cell when they become alive and part of the cell/body they infected (us), since viruses assimilate their DNA into our cells it might have been harder for the immune system to detect that something is off or wrong because well the cell the virus infected TECHNICALLY belongs to us and by the time the immune system kicks in, virus has multiplied a lot and have killed the cell and spread to other parts through blood.

So evolutionarily, it might have made sense to save these memory cells for these kind of viruses/pathogens that are not detectable easily, so if and when they get detected, the response is strong. Also, it might also be possible we keep getting infected with these from time to time and each time the memory cell kick in and kill them before we even get sick and the immunity kinda resets.

As I said it’s mostly speculation after the genetics of the memory cells part. But these are my thoughts

Hope this helps, feel free to ask any questions:)

What I’m reading here is not exactly correct and more importantly does not correctly answer your question. Bacteria and viruses *can both* be candidates for lifelong immunity or limited/no lasting immunity. The reasons for this come down to antigenic variation- ie the ID tags that the bacteria/virus carry that your body use to identify it. Basically some viruses and bacteria are stable in design. They look the same. Measles is measles is measles (To be comprehensive, over 20 types of measles have been identified per the WHO, but they all show the same ID tags, so our body recognizes them as all the same). However, some bacteria or viruses have lots and lots of variations of ID tags, often ones that recombine and mix together to make new ones (This is where the seasonal flu comes from) (Sometimes the genetics of species specific strains mix and create those really really bad flu outbreaks like the “swine flue” and “bird flu” pandemics that happens years ago.)

With Neisseria gonorrhoeae, it regularly changes its ID tags (It’s pili genes get spliced into new, novel ones). The end result is that every gonorrhea infection is unique. Or at least unique enough that you haven’t had it before. I’ve never looked into just how many variations of pili antigens it can express but safe to say its way more than the number of times any given human would contract gonorrhea (I hope….). The viruses that cause Hepatitis C work the same way. They regularly change their external ID tags so that our bodies can’t recognize them if they were to infect us again (though Hep C tends to be a very chronic disease). This is the main reason there is no effective vaccine for Hep C (but there is for A and B).

Syphilis is an interesting one. I had to read a little bit to answer but in layman’s terms. Syphilis is hard to study, incredibly invasive, and also has enough genetic variation that making a vaccine is challenging (but not impossible), however, because it responds so well to penicillin, need for a vaccine is lessened so it’s taken a bit of a back seat. Someone can feel free to correct me if I’m wrong. Additionally, regarding syphilis, it can establish a ‘latent infection’ in your body, essentially hiding for a time and then returning with a vengeance. While this means nothing on its own, it does speak to the resilience syphilis has as a bacteria and its ability to evade your immune system. I think an easy way to think about this is that something that can hide in the belly of the beast can certainly find its way in again. Common herpes viruses work the same way. If you have chicken pox as a kid, that virus never goes away, it hides in your nerves and can come back out as shingles when you are older.

Finally, with Strep throat (which is caused by a group of bacteria called “group A streptococcus,” it’s the similar issue to gonorrhea. The virus has too many subtypes, too many ID tags, and can change its ID tags over time. You never heard of a kid getting strep throat 200+ times. But that’s what it would take to become immune to all the versions of it, rendering you properly “immune” to strep throat.

As bonus, the common cold works the same way. Typically caused by a class of viruses called rhinoviruses, there’s simply way way too many types floating around, all carrying different ID tags so your body doesn’t recognize them as the same punk kids who tried to sneak into the bar with fakes just last month. If someone caught the common cold enough times, you’d probably eventually become immune to all of them (assuming your immune system is healthy).

This in part explains the admittedly anecdotal phenomenon I’ve heard told time and time again by my medicine colleagues that pediatricians that just start out practice tend to get sick a lot in their first year of practice but then slowly stop getting sick over time. They see a bunch of kids with colds and other viruses and catch them themselves, but as they practice over time, they start to have caught most of the ones endemic to the area and so get sick very rarely. Hence many stories of the 70 year old pediatrician picking up sneezing, slobbering sick children and not getting sick while the new blood keeps their distance, washes their hands carefully and still gets it.

Anyways, hope that helps.

Edit: Clarity and a missing clause.