As soon as the days get shorter and the temperatures drop, our immune system enters another particularly intense period. Colds and other infections are going around—and yet people react surprisingly differently to the same pathogens. Have you ever wondered why the fall cold season knocks your partner out of commission for days, while you yourself might only notice a brief scratchy throat? Or why some people seem to get through the cold season unscathed, while others catch every infection that comes their way?
For a long time, the answer was sought primarily in our genes. But modern research shows that our immune system carries far more than just the genetic blueprint we inherited from our parents. Our immune system is constantly interacting with our environment—and these experiences can have an impact even at the molecular level.
A recent study demonstrates particularly impressively just how individualized this defense system actually is. Scientists at the Salk Institute have investigated how genetic predispositions and environmental influences shape the epigenetic makeup of human immune cells. Their findings provide new insights into why the immune response varies from person to person. The study was published in the journal *Nature Genetics*.
The Immune System is Not a Rigid Shield
When people talk about the body’s own defenses, many initially think of antibodies, white blood cells, or the next wave of colds. In fact, the immune system is a highly complex network of cells, tissues, and signaling molecules that must constantly switch between different tasks.
Its job is to recognize and fight pathogens while, at the same time, sparing the body’s own tissues as much as possible. Some immune cells respond to a threat within a short time. Others can remember previous encounters with a pathogen and react more quickly upon renewed contact.
The immune system does not remain unchanged over the years. Infections, vaccinations, environmental factors, and other experiences can influence how certain immune cells later respond to stimuli. This is precisely where the new research comes in.
Why Two People React Differently to the Same Pathogen
At first glance, the question seems simple: If two people come into contact with the same virus, why does one develop only mild symptoms, while the other becomes significantly more ill? One possible explanation lies in the individual combination of genetic makeup and life history.
A research team led by scientists at the Salk Institute examined blood samples from 110 people. A total of 171 samples were analyzed. The participants had different genetic traits and different histories of exposure to pathogens and other environmental factors. These included, among others, influenza, HIV-1, MRSA, MSSA, and SARS-CoV-2, as well as anthrax vaccination and exposure to organophosphate pesticides.
The researchers examined various types of immune cells, including T cells, B cells, monocytes, and natural killer cells. They were particularly interested in determining which changes are related to genetic makeup and which are linked to experiences and environmental influences. The result: Both factors leave different molecular traces.
What the Epigenome Has to Do With this
This brings us to a term that is appearing more and more frequently in modern biology: the epigenome. Put simply, our genetic material can be compared to a comprehensive blueprint. But a blueprint alone does not explain which parts of a cell are currently active. This is where epigenetic mechanisms come into play.
Chemical marks on the genome can influence which genes are expressed more or less strongly. The DNA sequence itself is not altered in the process. This means that the genes remain essentially the same, but their activity can change.
This is particularly interesting for the immune system. That’s because immune cells must be able to respond flexibly. They are supposed to recognize a pathogen, initiate an appropriate immune response, and then return to a controlled state.
The scientists found evidence that genetically determined and experience-influenced epigenetic changes do not simply affect the same regions of the genome. Experience-induced changes were found particularly frequently in regulatory regions that are important for the regulation of cell activity.
In a Sense, the Immune System Maintains a Molecular Memory
Particularly fascinating is the idea that our immune cells, in a sense, bear traces of past experiences. An infection that has been overcome is not simply over and therefore biologically insignificant. Certain immune cells possess a memory and can recall previous encounters with pathogens. The current study expands on this picture: even at the epigenetic level, environmental experiences can be linked to changes in immune cells.
This does not mean that every experience permanently “programs” the immune system. Rather, the researchers show that genetic predispositions and environmental influences can leave behind different epigenetic patterns, and that these patterns vary depending on the type of immune cell.
It is precisely this individuality that could play a greater role in the future. A better understanding of why immune cells from different people react differently could, in the long term, contribute to more personalized strategies in prevention, diagnosis, and treatment.
Genes are Important – But they Don’t Tell the Whole Story
For a long time, health was often viewed primarily through the lens of our genes. Our genetic makeup undoubtedly influences numerous traits and disease risks. However, modern research increasingly shows that genes and the environment cannot be considered independently of one another. The immune system is a good example of this.
Over the course of our lives, our genetic makeup interacts with infections, vaccinations, diet, environmental factors, stress, sleep, physical activity, and many other influences. Not all of these factors have the same impact, and not all of them can be easily separated from one another.
Above all, the new study demonstrates how complex this interaction is at the level of individual immune cells. The scientists were able to distinguish between genetically determined and experience-related epigenetic changes and examine their different distributions within the epigenome.
This also makes it clear that a “strong immune system” is not a simple state that one achieves once and then maintains permanently. The body’s immune system is a dynamic system that is constantly interacting with its environment. Digestion also plays an important role, as there is a close connection between the gut and the immune system. The gut microbiome and its metabolites can influence the intestinal barrier and various aspects of immune regulation.
What Diet and Nutrients Have to Do with the Immune System
Naturally, this topic quickly raises the question of how diet influences the immune system. For the immune system to function normally, the body requires an adequate supply of various nutrients. These include, among others, vitamin C, vitamin D, vitamin A, vitamin B6, vitamin B12, folate, iron, zinc, selenium, and copper. They perform various functions in the body and are involved, among other things, in the normal functioning of the immune system.
However, it’s important to note that more is not automatically better. Dietary supplements can be a useful addition to a balanced diet, but they should not generally replace it. What matters most is that the body receives an adequate supply of the nutrients it needs. Nor does the new Salk study provide evidence that certain dietary supplements can prevent or reverse the epigenetic changes observed in the study. Rather, it examines the fundamental relationships between genetic factors, environmental influences, and the epigenome of immune cells. This distinction is particularly important: The fact that lifestyle factors influence the immune system does not automatically mean that a single product can specifically alter this effect.
The Immune System Needs More than a Single Nutrient
The body’s immune system does not function like a single switch that can simply be “turned on.” It consists of numerous interconnected processes. Therefore, general health depends not only on individual nutrients but also on the living conditions under which the immune system operates. Adequate sleep, regular exercise, a balanced diet, and as little chronic stress as possible are among the fundamental factors that make up a healthy lifestyle.
Age also alters the immune response. Over the course of a lifetime, the composition and functioning of various immune cells change. At the same time, the body accumulates more and more experience with pathogens and other environmental factors. This helps explain why our immune system, in the truest sense of the word, has a personal history.
Why Research Is Moving Toward Personalized Prevention
Scientists at the Salk Institute see their newly created atlas as a potential foundation for further research in the long term. The larger such datasets become, the better researchers will be able to investigate which epigenetic patterns are associated with specific infections or disease risks.
In the long term, a more personalized approach is also conceivable: If certain molecular signatures prove to be reliable, they could one day help to better assess individual disease progression or tailor prevention strategies more precisely.
However, medicine is still a long way from that. For now, the current study provides a scientific foundation and highlights correlations. It is not a diagnostic test for individual patients, nor is it a guide that can be used today to predict how someone will react to the next infection.
The Body’s Own Defense System is as Unique as We are
Perhaps this is precisely one of the most interesting findings: Our immune system is not simply a pre-programmed defense mechanism. It arises from the interplay between what we have inherited from our parents and what our bodies experience over the course of our lives. Infections and vaccinations leave behind immunological memories. Environmental factors can be linked to molecular changes. And genetic differences influence how individual immune cells respond to such influences.
Current research thus brings to light what is constantly happening in the body anyway: the immune system adapts to its environment. This knowledge opens up interesting perspectives for health research. After all, the better we understand why the immune response varies from person to person, the more precisely we will be able to investigate in the future how health and disease risks can be influenced on an individual basis.
What Does this Mean for Everyday Life?
Our immune system doesn’t develop overnight. It’s constantly in contact with our environment and reacts to whatever it encounters. The new research therefore makes one thing particularly clear: Health is not a static state, but rather an interplay between our genetic makeup and the experiences our bodies undergo over the course of a lifetime.
That doesn’t mean we can “program” our immune system at will. But it’s worth providing it with favorable conditions in our daily lives. Adequate sleep, regular exercise, a varied diet, and a good supply of essential nutrients are among the simple adjustments that can be integrated into daily life over the long term. Especially during the cold season, it doesn’t have to be complicated: eat a balanced diet, drink enough fluids, stay active, and make sure your body gets enough rest.