Memory B-cells are a type of immune cell that play a crucial role in the body's defense against infections. After the body encounters a pathogen, such as a virus or bacteria, B-cells can differentiate into memory B-cells. These cells remain in the body long after the infection has cleared, providing long-lasting immunity. When the same pathogen invades again, memory B-cells quickly recognize it and produce specific antibodies. This rapid response helps the immune system eliminate the pathogen more efficiently than during the first encounter, leading to a faster and stronger immune response.