Ask the Expert

Professor Covert says: All cells, even single-celled organisms like bacteria, are incredibly complicated systems that live in an even more complex environment. Individual cells frequently communicate with their neighbors. Cells don’t talk or think, of course, but they certainly have evolved similar ways of cooperating. One common method of communication is by producing signals, such as chemicals or electrical pulses, which can be detected by other cells, who respond by producing signals of their own. This ability to communicate and work together enables cells to do amazing things – with results that profoundly affect our lives.

For example, the immune system consists of many different cell types, which work together to rid our bodies of harmful viruses and bacteria. Preventing these invaders from causing disease is a complicated task, and accordingly, there are many types of cells which contribute to the immune response. First, immune cells called antigen-presenting cells find the invading cells. To let other cells know that they have found a threat, they produce a chemical message and send it out to the body. This signal alerts another kind of cell, called a helper T cell, which is able to recruit cells called phagocytes to swallow and destroy the invaders. This division of labor allows the immune system to be able to react and adapt to new harmful pathogens, and is only possible through cell communication.

Another great example is in the brain, where neurons communicate with neighboring cells by electrical coupling or chemical transmitters through cell-to-cell connections called synapses. The pattern and strength of these synaptic connections influence our sight, smell, thoughts, learning, memories, and emotion – just to name a few. And the brain and the immune system are far from the only examples. If you look into the biology of almost any interesting thing your body can do, from your hearing to your heartbeat, you will find that cell communication plays a vital role.

Recently, scientists have been very surprised to discover that this cellular teamwork is not limited to complex animals like humans but seems to be almost as ancient as life itself. For example, scientists have learned that microscopic bacteria, with far fewer genes than we have, can also communicate. Why would such simple cells want to talk to each other? One reason has important consequences for our health. Individual bacteria living in your body are too small to give you a disease by themselves, but a large gang of them can make you sick. Because of this, some bacteria like to know how many of their “friends” are around before they attack. Each individual bacterium sends out a chemical signal, kind of like a roll call in class. When enough of them are “present” — when the concentration of that chemical signal goes above a certain level – they turn on the genes to start the process of making their host sick. This phenomenon of cells communicating with each other to find out how many cells are nearby, and changing their behavior accordingly, is called “quorum sensing.”

Ultimately interactions between different cells, as well as the complex behaviors that result from this communication, are very difficult to determine or predict. Systems biology is a new field that focuses on using mathematics and engineering tools to simulate these networks of cells and signals in a computer, in order to better understand the underlying biology behind cell behaviors. By understanding cell communication more completely, we may be able to design drugs which block bacterial messages, or give a megaphone to the warning signals created by your immune system.