B Lymphocytes

Author: V. Dimov, M.D., Allergist/Immunologist and Assistant Professor at University of Chicago
Reviewer: S. Randhawa, M.D., Allergist/Immunologist and Assistant Professor at NSU

B-cell development


Hematopoiesis. Image source: Wikipedia.

B cells undergo only negative selection, whereas T cells undergo both positive and negative selection.

B Cell Types (click to enlarge the image).

B cells are CD45+ CD3- CD19+ or CD20+ cells.

Naive B cells are CD19+ surface IgM (sIgM)+ cells.

Mature B cells are CD19+ CD20- sIgG+ cells.

Memory B cells are CD19+ CD27+ sIgM+ cells.

Switched memory B cells are CD19+ CD27+ sIgM- cells (the majority of B cells in CLL are CD5+).

B-Cell Activation by Antigen (Ag)

Activation of B cells. Image source: Wikipedia.

The activation of B cells occurs when 2 Ig receptors are bridged (cross-linked) by antigen (Ag). This process transmits a signal to the cytoplasm via 2 molecules (Igα and Igβ). All these structures together form the B-cell antigen receptor (BCR) complex.

The T cells regulate B-cell proliferation and differentiation which takes 3-7 days. Thereafter, some activated B cells (called centroblasts) migrate deep into the lymphoid follicles and proliferate rapidly, forming the dark zone of the germinal center. B cells also give rise to a generation of plasma cells and memory B cells. Those memory B cell enables the host to mount a rapid and stronger secondary immune response with a subsequent encounter with the same antigen.


Germinal Centers. This video describes the formation and function of germinal centers. This video is from: Janeway's Immunobiology, 7th Edition, Murphy, Travers, & Walport. Source: Garland Science.


Lymphocyte Trafficking. This video describes how lymphocytes travel through the blood stream and into a lymph node. This video is from: Janeway's Immunobiology, 7th Edition, Murphy, Travers, & Walport. Source: Garland Science.

B-cells are the only cell types that synthesize antibody molecules.

The earliest B cell that produces immunoglobulins is the pre-B lymphocyte. An adult produces 2-3 grams of immunoglobulin every day

Light chains κ and λ are encoded on diffrent chromosomes - κ is encoded on chromosome 2 and λ is encoded on chromosome 22. An immunoglobulin molecule has either κκ (60%) or λλ (40%) but never one of each. An individual B lymphocyte will produce only κ or λ chains but never both.

CDs on Different Cells

CD25 and CD3 are found on all T cells. CD25 is a receptor for IL-2.

CD19 and CD21 are found on all B cells.

CD16 are found on natural killer (NK) and NK T cells. CD16 is a receptor for IgG.

IL7 activates naive T cells. BAFF activates naive B cells.


T and B Cells - Naive and Memory Cell Markers (click to enlarge the image).

What chemokine attracts naïve B cells to lymph nodes?

CXCR5. CXCL13 binds to CXCR5.

What chemokine attracts naïve T cells to lymph nodes?

CCR7. CCL19 and CCL21 bind to CCR7.

Mnemonics

T cells have CD 3, 4 and 8 (double, 4 x 2)
B cells have CD 19, 20 and 40 (double 20 x 2)

Stem cell CD34+
Plasma cell CD 38+

Surface Markers

L
Ligands on
Lymphocytes

CD40L on T helpers (CD4+)
FAS-L on CTL 9CD8+)

CD40 on B cells
FAS ("death signal") on cells to be killed by CTLs


Gene Recombination. This video shows how gene recombination affects immunoglobulins. This video is from: Janeway's Immunobiology, 7th Edition Murphy, Travers, & Walport. Source: Garland Science.

B cell activation

Complement receptor CD21 (CR2) activates BCR if the antigen is opsonized by C3b component of the complement. CR2-CD19-CD81 complex is expressed on the surface of B lymphocytes. CD19 is probably the best marker of B-lymphocytes. CD19 is a co-receptor with CD21.

When CD21 (CR2) interacts with C3d, the complex is brought into the BCR. CD19 has an ITAM that is phosphorylated, thus recruiting Lyn to enhance phosphorylation.

Complement receptors (click to enlarge the image).

Related Reading

Medical Immunology Syllabus. Columbia University.
In the Clinic - Dr. Robert Wood, MD, Discusses the IgE Blood Allergy Test. InsiderMedicine.ca (video).
Variations in Receptor Gene Contribute to Asthma Exacerbations. Medscape, 01/2008; J Allergy Clin Immunol 2007;120:1285-1291.
Anti-IgE (omalizumab): A new therapeutic approach for chronic rhinosinusitis. JACI, Volume 121, Issue 1, Pages 257-258 (January 2008).
FIT Corner Q & A from 5th edition of Cellular and Molecular Immunology, edited by Abul K. Abbas and Andrew H. Lichtman. ACAAI, 2004.
Nuocytes are previously unknown members of the lymphoid lineage. Nature, 2012.

Video

3D Medical Animation: Antibody Immune Response

Published: 12/13/2007
Updated: 02/05/2012