T cells and B cells are white blood cells that are important cells for adaptive immunity. Like all blood cells, they are made in the bone marrow. While B-cells mature in the bone marrow, T-cells travel through the bloodstream to the thymus (a small organ between the lungs and behind the sternum) and mature there. Broadly speaking T cells can be divided into two different types, ‘killer T-cells’ and ‘helper T-cells’.
Regulatory T cells (also called Tregs) are
another types of T cells.
Tregs have a role in regulating or suppressing other cells in the immune system. 2018 Nobel prize in Physiology and Medicine is related to negative immune regulation. Find more innobelprize .org
Killer T cells also known as cytotoxic T cells (CTL) hunt down and destroy cells that are infected with germs or that have become cancerous while helper T cells help B cells to make antibodies. T helper (TH) cells express CD4 molecules and are restricted to recognizing antigens bound to class II MHC molecules, whereas T cytotoxic (TC) cells express CD8 and are restricted to recognizing antigens bound to class I MHC molecules. Cytotoxic T cells kill cells that are infected with viruses or altered self-cell with toxic mediators (perforin and granzymes).
B cells are major cells of humoral (antibody-mediated) immunity, effector B cells (plasma cells) produce antibodies that circulate, capture and destroy antigens.
Circulating helper T cells recognize
When a naïve (virgin) B cell first encounters the antigen that matches its membrane-bound antibody, the binding of the antigen to the antibody causes the cell to divide rapidly (clonal expansion); its progeny differentiates into memory B cells and effector B cells called plasma cells. Plasma cells secrete antibodies which act as major effector molecules of humoral immunity.
Some of the major differences between B Cells and T Cells are tabulated below:
| Features | B Cells | T Cells |
| Maturation | Bone Marrow (Bursal equivalent) | Thymus |
| Involvement of MHC molecules | None required | Required to display processed antigen |
| Recognition of Antigen | B Cells can recognize and bind to soluble antigens. | T-cell receptor (TCR) does not recognize the free antigens. T cells can recognize an antigen only when it is associated with self MHC molecule on the surface of a self-cell (either an antigen-presenting cell or altered self cell or on a virus-infected cell and graft). |
| Chemical nature of antigen | B cells recognize an enormous variety of antigens such as proteins, polysaccharides, and lipids. | T cells recognize protein epitopes displayed together with MHC molecules on self-cells, but some lipids and glycolipids are presented on MHC-like molecules. |
| Interaction with antigen | Involves binary complex of membrane Immunoglobulin and Antigen | Involves ternary complex of the T-cell receptor, antigen, and MHC molecule |
| Epitope properties | Accessible, hydrophilic, mobile peptides containing sequential or nonsequential amino acids | Internal linear peptides produced by processing of antigen and bound to MHC molecules |
| Antigen Specificity | Antigen specificity of each B cell is determined by the membrane-bound antigen-binding receptor (antibody) expressed by the cell. | Antigenic specificity of T Cells is determined by antigen-binding T-cell receptor (TCR) on T Cells. TCR genes are capable of generating on the order of 10^9 unique antigenic specificities. |
| Peripheral Blood | 10-15% of total lymphocytes | 70-80% of total lymphocytes |
| Antigen recognition receptors | Membrane-bound immunoglobulin (IgM or IgD complexed with Igα /Igβ) molecules serve as receptors for antigens. | T cell receptors (TCR) complexed with CD3 (signal-transduction element of the T-cell receptor) |
| CD markers | CD32/FcγRII (Receptor for Fc region of IgG), CD35 or CR1 Receptor for complement (C3b), and CD40 (Signal transduction) | CD3, CD4 (adhesion molecule that binds to class II MHC molecules; signal transduction), CD8 (adhesion molecule that binds to class I MHC molecules; signal transduction), CD28 (receptor for co-stimulatory B7 molecule on antigen-presenting cells), CD45 (a signal-transduction molecule) |
References and further reading:
- Cellular and Molecular Immunology, 9th Edition
- Kuby Immunology, 8th Edition
- Roitt’s Essential Immunology, 13th Edition
