They started by gathering a group of kids in the San Diego area who had recurrent tonsillitis, matched them with similar children who got normal tonsillitis, then looked at various markers for their immune systems to see what differed between the two groups. (As an interesting side note, about 75 percent of the kids with recurrent infections were female, even though it was 50-50 in the non-recurrent group. Crotty says he doesn't have any explanation for why that was, but that it's certainly interesting and should be investigated further.) The study got into a lot of detail about the specific types of cells involved in mounting the body's response to strep, but we're going to simplify it down a bit for you. Basically, tonsils have sites inside them called germinal centers, which produce and mature different types of immune cells that are crucial for identifying pathogens. Given how frequently the kids with recurrent tonsillitis had strep infections (12 times more, to be exact), you'd expect to find more evidence of an immune response to Streptococcus—for example, you'd think those kids would have a lot more antibodies against strep. But these researchers found that children with recurring infections actually have less of a response, not more.