The COVID-19 pandemic has highlighted something doctors have always been clear about in the general population: the human immune system is highly variable. How can a virus cause cold symptoms in one person, and instead send the person next door to the ICU, if the infectious agent is the same and the body's basic defense mechanisms are the same?
The easy-to-understand explanation is that these defenses do not work the same way for everyone. The problem is trying to explain the reason for these differences, because it is not simple. There's clearly a genetic basis that makes some people better protected against certain threats than others from the start, although we don't know all the details yet. But it is known that very diverse external factors also affect it.
Something unexpected has just been discovered: tobacco. According to a recent article published in the magazine natureSmokers suffer from weak immunity, especially those who remember infections, and this certainly makes them more susceptible to diseases.
Innate and adaptive defenses
The human immune system, like that of other mammals, is a complex network of proteins, cells and components that work in a perfectly coordinated way to quickly destroy not only microbes that invade us, but also cells that do not behave as they should. They should (for example, those that are about to become malignant or those that have grown old and no longer function properly). Without this protection we will not last long. That's why it's so important that it works well.
Our defenses are divided into two large groups, according to the way they work: those that belong to the innate immune system (which is non-specific but fast and evolutionarily older) and those that belong to the adaptive system (more subtle, and relies on cells called Lymphocytes Which make antibodies that recognize specific invaders and have a memory for future reinfections).
For the response to be appropriate for each situation, they must be able to act independently or together. Cytokines are a family of proteins made by blood cells that are precisely involved in coordinating the two pathways.
Tobacco, obesity and cytomegalovirus
The group of Dr Violine Saint-André, a computational biologist at the Pasteur Institute in Paris, set out to measure the difference in the production of thirteen different types of cytokines from blood samples taken ten years ago from a thousand healthy volunteers from Brittany, with the aim of better understanding personal differences in responses. Immunostaining.
To activate immunity, both innate and adaptive, researchers exposed blood to dozens of microbes and similar agents, then measured the different types of cytokines made. The final step was to compare the results with the clinical information of the volunteers in the data bank.
Thus they found an association with smoking: smokers had reduced production of cytokines, especially those related to the adaptive system, even if they had quit smoking years ago. The blame for these prolonged effects appears to be tobacco-induced epigenetic changes (chemical modifications to DNA that are, in principle, reversible), which alter the functioning of genes important for immunity.
The same study found two other factors that can interfere with the functioning of the immune system: having a body mass index (BMI) higher than what is considered healthy (i.e., obesity) and infection with cytomegalovirus, a microbe that usually gives mild symptoms.
Confirm with more details
The results still need to be confirmed in a larger and more diverse group. The same researchers are studying samples from Africa and Asia to compare them with European samples, in addition to new samples from the original volunteers, to find out how their immunity developed after a decade.
However, these data fit with previous clinical observations, such as a study published at the end of the 1990s by Dr. Jordi Almiral and other members of the Mataró Health Federation had already seen a link between smoking and susceptibility to diseases such as pneumonia, which persisted for years after quitting smoking.
There are many factors that can modify the immune response. Gender is the most well-known: We have known for a long time that women's immunity is very different from men's because of the role played by hormones. The other reason is aging: with age, immunity loses its strength. Now we can add some other factors to the list.
The good news is that, contrary to what we already know, some of these diseases can be controlled. Quitting smoking and maintaining a balanced BMI not only protects against cancer, cardiovascular disease and aging, but also helps keep the immune system functioning at full capacity. A good reason to strive for it.
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