B-cells are a type of white blood cell that play a crucial role in the immune system. They are responsible for producing antibodies, which are proteins that help identify and neutralize harmful invaders like bacteria and viruses. When B-cells encounter these pathogens, they can quickly multiply and create specific antibodies tailored to fight off the infection. Once B-cells are activated, some of them become memory B-cells. These cells remember the specific pathogens they have encountered, allowing the immune system to respond more rapidly if the same invader attacks again in the future. This memory is what makes vaccinations effective, as they train B-cells to recognize and combat specific diseases.