I put in the quote from the Tysabri page but since you can't cut and paste here with out providing the link, I had to provide the link to where I got the information.

If you go to the link and scroll down, or use the search function with the key word "antibodies" you will find the information I was referring to when you said they were sending off your blood to be testing for antibodies.

Also, in the same part of the medication guide, there is some information about allergic reactions.