Doughnut though we may be, our digestive tract is infinately more sensitive to the outer world than our skin is. Many of the things that we eat and/or breathe do find their way into our bodies, if for no other reason than there was nothing particular about them that made the digestive system reject them. If the antigen itself is as small as a common monomer, I doubt it would find much resistence. I am not saying we should deliberate introduce potentially harmful things into our bloodstreams, but a good does of everyday bacteria and other anigens and pathogens is healthy. You can build up a full library of memory cells that will fight off sicknesses before you even have a chance to notice them. Btw - it's not all trash science, and being a microbiologist as you so claim, I would expect you to know all about the effects of anit-bacterials/anti-biotics on our delicate internal fauna as well as how they toughen up enviornmental bacteria. 0.o