Good correction, thanks. I must have been thinking of hops that was added later to preserve the beer. Boiling is a much simpler answer.

Alcohol is an immunosuppressant, yes. To clarify my point, It's proper function is as a solvent in, say, cough syrup, to ensure correct mixture. It can change the rate at which medicines are broken down by the body to some degree while also acting as an extremely mild sedative as well.