Tracy suffered from chicken pox in her childhood. at the age of 25, she gets it again. however, this time she recovers with minimal treatment or medication. this was possible due to what cells produced by what immune response.

So its acquired immunity and the cells responsible are the B lymphocytes that produces antibodies against the virus. Memory is keep since first encounter of the virus by the immune system by way of the antibodies that was initially produced. The antibodies are there already, which makes it fast to act upon when expose again.