Some are also marked by CD5 surface Ag. If do a transplant with fetal liver, get both. B-1 cells are found predominately in the peritoneal and pleural cavities, not in LN and spleen. Tend to display a much more limited V region repertoire than B-2 cells, with lots of self reactivity and recognition of bacterial antigens. Many lack N region insertion and there is little to no somatic mutation.
Reactivity is broad specificity, low affinity.
In mice and humans, B cells at birth are mostly B-1. Ab they make is heavily skewed toward self Ags. But within short time, B-2 come to dominate. In autoimmune disease the B-1 proportion rises and they now show up in LN and spleen. Ab they make is mostly directed to self Ags.