Extroverts may have stronger immune systems

The conscientious group ("introverts") had lower levels of inflammation, which is an immune response.

Inflammation can also be caused by stress.

It's a lot more plausible that the conscientious group is just less stressed.

The researchers likely invented the immune hypothesis in order to tie in with another study showing the same immune/extrovert link.

So shake hands with more people, then lick your hands. What doesn't kill you will make you stronger.

Our immune system is adaptive. I find it unbelievable that scientists can draw an un-flawed conclusion considering that our immune system learns over time with the number of exposures.