B1 cells are a sub-class of B cell lymphocytes that are involved in the humoral immune response. They are not part of the adaptive immune system, as they have no memory, but otherwise, B1 cells perform many of the same roles as other B cells: making antibodies against antigens and acting as antigen-presenting cells. These B1 cells are commonly found in peripheral sites, but less commonly found in the blood. These cells are involved in antibody response during an infection or vaccination. [1]
There are two types of B1 cells subsets, B1a cells and B1b cells.[1] B1b cells have been shown to be capable of memory responses.[2] B1b cells also can recognize protective antigens in bacteria, which is unique because they are targeting something internal.[1]