We often get sore throats once or twice a year, and it clears in a few days sometimes without any antibiotics. I was wondering why doesn't our body become immune after clearing a sore throat?
It should be noted that there are many non-pathogenic causes of sore throat, and I would suspect that you are not always distinguishing these causes from actual illness.
- In most cases, it would not be possible to build a response (immunological or otherwise) to avoid reacting to these stressors.
Bacteria and viruses mutate frequently in ways that make your immune system unable to properly recognize them to ward off initial infection.
- Your immune system recognizes specific pathogens based on structural characteristics. If those characteristics change when pathogens mutate (which happens fairly frequently), your immune system will not recognize it as readily (or initially at all).
Sore throats can be caused by many things. (e.g., see here, summarized below):
First off, a sore throat can be the result of many things unrelated to illness:
- Excessive talking,singing,shouting,etc.
- Muscle Strain
- Gastroesophageal reflux disease (GERD)
As a result, at least 30+% (higher in adults) of reported sore throat cases (and supposedly many more unreported cases) are not due to any type of illness.
Further, a number of pathogens can cause a sore throat:
- Rhinovirus, coronavirus, influenza, parainfluenza, adenoviruses, Epstein–Barr, etc.
- (see here for one estimate of relative etiologies).
- A number of bacterial infections can cause a sore throat. The most common is Streptococcus pyogenes (aka "Strep A").
It turns out that pathogen-caused pharyngitis is fairly common. Supposedly 10% of adults with sore throats have strep, and around 70% of children pharyngitis cases seen by doctors are either virally or bacterially caused.
- However, it should be noted that only 20-30% of children and just 5-10% of adults have bacteria to blame for their sore throat, with viral infections being much more common. (source: IDSA).
Sore Throat Frequency
It turns out that sore throats are fairly common; Jones (2004) determined that about 7.5% of people have a sore throat in any three-month period. Further, on average, adults get a sore throat two to three times a year and children about five times a year (Tamparo 2011 and Rutter & Newby 2015), so your personal experience is fairly average.
Because viral causes and non-pathogenic causes make up an overwhelming percentage of overall sore throat cases, it shouldn't be surprising that most sore throats clear up without the use of any antibiotics.
As for those that are caused by pathogens:
Why no Immunity?
Bacteria and viruses both mutate fairly quickly (see Antigenic Variation, Antigenic Drift and Antigenic Shift), so it shouldn't be surprising that you're capable of having an immune response to pathogens throughout life.
If we consider just strep alone, it mutates/reemerges with improved fitness frequently (e.g., see Bao et al 2016 and their citations)
And see Sanjuán et al. (2010) for a reviewof viral mutation rates.
So not only are there a number of pathogens that can cause sore throat, but each of these pathogens can mutate. That leaves you with a fairly sizable number of potential invaders that can illicit a sore throat.
Let's See How Your Immune System Responds:
Your immune system contains cells that can be split into two broad groups: cells that belong to the adaptive immune system, and cells which belong to the innate immune system. [See here for a simple explanation].
Innate Immune system: consists of cells responsible for initial detection of pathogens, recruitment of other immune cells, activation of the complement system, engulfment and (more immediate) destruction of pathogens.
Adaptive immune system: consists of cells which coordinate to develop a memory of the infections they've seen previously in order to mount a faster, more pronounced immune response to repeat pathogens.
Depending on the kind of foreign invasion, two different immune responses can occur in either of these 2 broader "systems": either a humoral response involving antibodies or a cell-mediated repsponse.
A general feature of the immune system is that these mechanisms rely on detecting structural features of the pathogen or toxin that mark it as distinct from host cells (see Chaplin 2010 for a review). The mechanisms permitting recognition of pathogenic/toxic foreign structures can be broken down into two general categories:
hard-wired responses encoded by genes that recognize molecular patterns shared both by many microbes and toxins that are not present in the mammalian host. This is the innate system described above.
responses that are encoded by gene elements that somatically rearrange to assemble antigen-binding molecules with extreme specificity for individual unique foreign structures. This is the adaptive system described above.
- Antibodies recognizes a unique/specific molecule of the harmful agent, called an antigen, and binds to it to tag it for immune attack.
Because the adaptive system is composed of small numbers of cells with specificity for any individual pathogen the responding cells must proliferate after encountering the antigen in order to attain sufficient numbers to mount an effective response against the microbe or the toxin. [Source: Chaplin 2010].
- This means that you can still experience some mild symptoms due to the invading pathogen.
The important take-away from all this, though, is that your immune response relies on structural "markers" on pathogens in order to recognize them. This is true for both innate and adaptive immune responses. If the physical/structural properties of a pathogen change (due to antigenic processes and mutations as mentioned above) your immune system will be slower (and possibly ineffective) in responding to an attack.
- The result, then, could be another one of those sore throats...
Bao, Yun-Juan et al. “Phenotypic Differentiation of Streptococcus Pyogenes Populations Is Induced by Recombination-Driven Gene-Specific Sweeps.” Scientific Reports 6 (2016): 36644. PMC. Web. 17 Mar. 2017.
Chaplin, D. D. (2010). Overview of the immune response. Journal of Allergy and Clinical Immunology, 125(2), S3-S23.
Jones, Roger (2004). Oxford Textbook of Primary Medical Care. Oxford University Press. p. 674. ISBN 9780198567820. Retrieved 4 August 2016.
Rutter, Paul Professor; Newby, David (2015). Community Pharmacy ANZ: Symptoms, Diagnosis and Treatment. Elsevier Health Sciences. p. 19. ISBN 9780729583459.
Sanjuan, R., Nebot, M. R., Chirico, N., Mansky, L. M., & Belshaw, R. (2010). Viral mutation rates. Journal of virology, 84(19), 9733-9748.
Tamparo, Carol (2011). Fifth Edition: Diseases of the Human Body. Philadelphia, PA: F.A. Davis Company. p. 356. ISBN 978-0-8036-2505-1.