B cell

B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system by secreting antibodies. Additionally, B cells present antigen (they are also classified as professional antigen-presenting cells (APCs)) and secrete cytokines.

In mammals, B cells mature in the bone marrow, which is at the core of most bones. In birds, B cells mature in the bursa of Fabricius, a lymphoid organ. (the "B" from B cells comes from the name of this organ), where it was first discovered by Chang and Glick, and not from bone marrow as commonly believed.

B cells, unlike the other two classes of lymphocytes, T cells and natural killer cells, express B cell receptors (BCRs) on their cell membrane. BCRs allow the B cell to bind a specific antigen, against which it will initiate an antibody response.

Development

B cells develop from hematopoietic stem cells (HSCs) that originate from bone marrow. HSCs first differentiate into multipotent progenitor (MPP) cells, then common lymphoid progenitor (CLP) cells. From here, their development into B cells occurs in several stages (shown in image to the right), each marked by various gene expression patterns and immunoglobulin H chain and L chain gene loci arrangements, the latter due to B cells undergoing V(D)J recombination as they develop.

B-1 cell

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. Notably, most B1 cells do not develop into memory B cells.

Origin

B1 cells are first produced in the fetus and most B1 cells undergo self-renewal in the periphery, unlike conventional B cells (B2 cells) that are produced after birth and replaced in the bone marrow.

Types

In January 2011, human B1 cells were found to have marker profile of CD20+CD27+CD43+CD70- and could either be CD5+ or CD5-, which has been debated since. CD5-CD72 is thought to mediate B cell-B cell interaction. B-1 B cells, in the mouse, can be further subdivided into B-1a (CD5⁺) and B-1b (CD5⁻) subtypes. Unlike B1a B cells, the B-1b subtype can be generated from precursors in the adult bone marrow. The B1a and B1b precursors have been reported to differ in the expression levels of CD138.