by Daniel Mendelson
While you laugh at your uncle’s corny dad jokes at the Thanksgiving table, your immune system is given a boost. This may not protect you from the terrible jokes, but it can certainly protect you from infections (1) and even some cancers! (2) Indeed, beyond reducing stress (1), laughter seems to reduce inflammation (2) and activate natural killer cells (NK cells), which are crucial immune cells (1-3).
A 2003 study by Bennett and colleagues found that people who laughed when watching comedy specials had more activated NK cells right after being humored than before. In addition, those who didn’t watch a comedy or who didn’t laugh at it did not exhibit this change in NK cell activation! (1) Similarly, another study found that those who watched a humorous film had 25% more activated NK cells after they watched the film (2). These findings suggest an association between laughing and the activation of NK cells.
That is interesting, but what are natural killer cells anyway?
NK cells are one of the many cell types that the immune system depends on to prevent, detect, and deal with infections from bacteria, viruses, and other unwelcome guests. Like all cells in our body, immune cells are like factories: they contain many workers in the form of proteins and other molecules that produce a variety of products. For example, NK cells have the machinery to produce molecules that send messages between cells and other molecules that can kill infected or cancerous cells (4). What a cell produces, though, depends on what is going on within and around the cell.
To detect what is happening inside and around them, cells have receptors that decorate the inside and outside walls of these factories. You can think of receptors as bells that can only be rung by specific molecules. There are several types of bells, each with a unique signal, and each detecting a specific type of molecule. When rung, the cell can deduce the presence of the specific molecules that ring this specific bell. In response to these signals, the cell produces—or stops the production of—specific molecules.
Already, this is a dizzying image. Yet, it gets more complex: different types of receptors might ring at the same time and influence the activities of the cell in complex ways. What’s more, cells are decorated with more than just receptors, and all these features are constantly being rearranged, added, and removed depending on the signals that the cell is receiving. Despite this intricacy, one thing is constant: every healthy cell has something called the Major Histocompatibility Complex I (MHC-I for short). Like a window, MHC-I displays what the cell is making to the outside world (4).
In an effort to conceal their presence from the immune system, viruses and cancers make the cells they infect remove these windows — just like vandals defacing and breaking factory windows (4). Luckily, NK cells have special receptors that can detect cells of yours that are missing MHC-I (4). When NK cells come across such a cell, they act quickly to kill the dangerous cell by releasing toxic molecules; this ensures that viruses don’t replicate and cancers don’t proliferate (4). In short, NK cells kill the fun of viruses and cancers so that ultimately, your body can get the last laugh!
While there are always some NK cells that are active, as Bennett’s study and others indicate, your uncle’s jokes encourage more of these NK cells to be on the lookout for danger (1,2).
While it is not yet clear how NK cells detect laughter, behaviours and moods beyond laughter clearly influence our immune systems. Stress, sleep, exercise, diet, and many other things you can control affect your immune system (3). While researchers continue to dig deep into these secrets, use the current understanding of our immune systems as a reason to laugh and enjoy life; after all, dying of laughter may really be keeping you alive!