Immune system reacts to threats

DEAR DOCTOR K: A friend heard about a study that said a person’s immune system changes with the seasons. That seems incredible to me. Do you know what she is talking about?

DEAR READER: I think I know the study she is referring to. Before describing what it found, it’s worth talking a bit about the immune system and also about genes.

First of all, that the immune system should change in response to any external circumstance should not be surprising. The immune system is constantly changing as it responds to a changing set of foreign threats. Different germs, different non-infectious foreign substances (such as pollen, animal hair, dust) are entering our bodies all the time. A healthy immune system is always refocusing its attack.

The immune system is like an army; it has many different types of cells that have different functions. Think of each group of cells as a platoon that does a particular job. It also has a hierarchy, with the cells at the “top” directing the actions of all the other cells.

For the cells of the immune system to function properly, the right genes in those cells need to be turned on (and others turned off) at the right time. In the past 30 years, scientists have developed ways of determining which genes in a cell are turned on and off.

The study was conducted by a scientific group in Europe that obtained blood samples from thousands of people. Some people lived well north (or south) of the equator, where the seasons are most dramatic. Others lived near the equator all year, where the seasons are the least dramatic.

In the blood samples, the researchers measured which immune system genes were turned on. They found some genes were turned on all year, without any seasonal variation. But in both hemispheres, some immune system genes were turned on differently during summer than during winter.

There are no practical applications that follow from this study. But I’m glad you asked about it. It underlines just how dynamic our immune system is to do its job.