Swelling as an indicator of immune activity

When you got your last vaccine, did your arm swell up locally?  You may have assumed that this meant your immune system was working hard in response to the vaccine, but is the relationship between swelling and immune activity really so straightforward?

External swelling is used as an indicator of the internal workings of the immune system in skin-prick allergy tests; similar tests are done on wild birds to see if immune function is affected by environmental contamination.  In our research, we aim to investigate the validity of the assumed relationship between swelling and immune activity.