B2b and B1b Cells

• B2b cells are conventional B cells distributed throughout the body and continually replaced in the bone marrow.
• B2b cells can recognize a vast range of epitopes.
• Immunoglobulin isotype changes accompany B2b cells and are associated with immunologic memory.
• B2b cells depend on T cells for activation.
• IgG and IgD are produced at high levels by B2b cells
• IgD is the dominant isotype on the surface of naive B cells.
• Continuous replacement in B-2 B cells refers to cells being regularly replenished from a source (bone marrow),
• B-2 B cells do not exhibit self-renewal.

B1b Cells

• B1b cells arise from the fetal liver and represent a transitional lymphocyte type.
• B1b cells are thought to be transitional.
• B1b cells assist during innate-related immunity and autoimmune disorders.
• The BCR repertoire and recognition in B1b cells are limited.
• More than half of IgA-secreting cells are of the B1b cell lineage.
• B1b cells self-renew in the periphery.
• B1b cells do not require T cell assistance or activation.
• B1b cells produce high levels of IgM.
• IgM, not IgD, is the dominant surface isotype on B1b cells.
• The cells result in very little memory

Follicular B cells

• Follicular B cells and marginal zone B cells are subsets that differentiate from B2b cells
• Follicular B cells dwell in lymph nodes.
• Follicular B cells maintain high diversity for antigen recognition.
• Follicular B cells are memory cells.
• Follicular B cells produce high levels of IgG.
• All follicular B cells are B-2 B cells

Marginal Zone B cells

• Marginal zone B cells migrate to the marginal zones of the spleen.
• Marginal zone B cells maintain limited diversity and antigen recognition.
• IgM is the primary isotype produced by marginal zone B cells.
• Memory antibody production in marginal zone B cells is unknown.
• Marginal zone B cells are considered a subset of B-2 B cells.
• B-2 B cells are the conventional B cells playing a central role in adaptive immunity.
• Marginal zone B cells are involved in rapid, innate-like immune responses, particularly against blood-borne pathogens.

B1 vs B2 Cells

• B1 and B2 cells originate from mature B cells.
• The cells leave the bone marrow and enter secondary lymphoid tissue.
• B 1b cells (transitional B cells) reside in the periphery.
• B 2b cells condense to follicular B cells in the lymph nodes or marginal zone B cells in the spleen.

Comparing B-1 and B-2 B Cells

• B-1 and B-2 B cells represent distinct B cell subpopulations with different locations, developmental origins, BCR diversity, antibody production profiles, and immune roles.
• B-1 B cells contribute to innate-like immunity and early protection, especially in mucosal tissues, focusing on natural antibody production.
• B-2 B cells are essential for adaptive immunity, producing diverse and highly specific antibodies tailored to encountered antigens and playing a critical role in long-term immune memory.

B-1 B Cells

• B-1 B cells are found in body cavities (peritoneal and pleural) and mucosal tissues.
• The cells are considered a self-renewing population arising during fetal development and persisting throughout life.
• The cells typically express BCRs with limited diversity, primarily producing antibodies with germline-encoded variable regions.
• The cells are known for producing natural antibodies, often polyreactive, recognizing common pathogens and self-antigens.
• The cells mainly produce IgM and some IgA antibodies.
• The cells are involved in innate-like immune responses, providing early protection against infections, especially in mucosal tissues.
• B-1 B cells contribute to the clearance of dying cells and participate in tissue repair and homeostasis.
• B-1 B cells can self-renew, maintaining their population and contributing to long-term antibody production.

B-2 B Cells

• B-2 B cells are found in secondary lymphoid organs like lymph nodes and spleen.
• B-2 B cells are generated from hematopoietic stem cells in the bone marrow throughout life.
• The cells express BCRs with diverse variable regions generated through V(D)J recombination, resulting in a wide range of antigen specificities.
• B-2 B cells are the main producers of antibodies in the adaptive immune response.
• They can switch antibody classes (isotype switching) and produce high-affinity antibodies, including IgM, IgG, IgA, and IgE, tailored to specific antigens.
• B-2 B cells play a central role in adaptive immunity by generating antigen-specific antibody responses.
• They participate in the formation of memory B cells and long-lasting immunity against pathogens.
• B-2 B cells are highly efficient at recognizing and responding to a wide variety of foreign antigens through their diverse BCRs.

Follicular B Cells and Marginal Zone B Cells

• These are subpopulations of B-2 B cells with distinct locations, functions, and roles in the immune system.
• Follicular B cells are central to adaptive immunity, generating specific, high-affinity antibodies.
• Marginal zone B cells play a role in innate-like immunity, providing rapid, initial protection against common pathogens, especially in the spleen's marginal zone.
• Both populations contribute to the overall immune response.