H! In the past, whenever I felt a bit under the weather and thought I was coming down with something, going for a run sometimes worked for me and the illness just went away. Maybe it's because I sweated out the germs? However, I don't think it's an ideal solution, and as I've gotten older, I don't do it anymore. If I don't feel well, I don't run.
An athlete is definitely more resilient than a non-athlete. For example, I run in the winter, breathe cold air, get rained on, and sometimes feel freezing, which probably toughens the body up quite a bit. I can't even remember the last time I was sick—like really, properly sick. I don't count mild colds.