T cells, also known as T lymphocytes, and B cells, also known as B lymphocytes, are two types of lymphocytes that play essential roles in the immune system. While both cell types contribute to the body’s defense against pathogens, they have distinct functions and characteristics. Understanding the differences is crucial for comprehending the complexity of immune responses. In this article, we will explore the functions, structure, and properties of, highlighting their unique roles in the immune system.
T cells, also known as T lymphocytes, are a type of lymphocytes that play a crucial role in the immune system. They originate in the bone marrow and undergo maturation in the thymus. T cells can be further divided into three main types: helper T cells, cytotoxic T cells (also known as killer T cells), and suppressor T cells.
Functions of T cells:
- Helper T cells: These recognize antigens presented by antigen-presenting cells (APCs) and play a key role in coordinating the immune response. They stimulate B cells to produce antibodies and assist in the development of killer T cells.
- Cytotoxic T cells: They are responsible for directly killing infected or cancerous cells. They recognize specific antigens displayed on the surface of infected cells or cancer cells and induce cell death (apoptosis) in these target cells.
- Suppressor T cells: Suppressor T-cells, also known as regulatory T cells, have a regulatory function in the immune system. They help maintain immune tolerance and prevent autoimmune responses by suppressing excessive immune reactions.
Structure of T cells
- T cells have specific receptors called T cell receptors (TCRs) on their surface that allow them to recognize antigens presented by APCs.
- TCRs are composed of two polypeptide chains, either alpha and beta or gamma and delta chains, linked together by disulfide bonds. Complementary determining regions (CDRs) within the variable region of the TCR provide specificity in antigen binding.
Cytokines are messenger molecules produced by T cells and used to communicate with other immune cells. They help regulate and coordinate the immune response. T cells are involved in immunotherapies such as checkpoint inhibitors, which enhance the immune response against cancer cells, and CAR T-cell therapy, where T cells are genetically engineered to target specific cancer cells expressing certain proteins. In summary, T cells play a vital role in immune responses by recognizing antigens, coordinating immune reactions, killing infected or cancerous cells, regulating immune tolerance, and producing cytokines to communicate with other immune cells.
What are B cells?
B cells, also known as B lymphocytes, are a type of lymphocytes that play a crucial role in the immune system’s humoral response. They mature in the bone marrow and are responsible for producing antibodies in response to antigens. Here are the functions:
Functions of B cells
- B cells produce antibodies that mark pathogens for destruction by other immune cells.
- They mediate humoral immunity by generating specific antibodies to neutralize invading pathogens.
- B cells differentiate into plasma cells (effector cells) and memory cells upon encountering antigens.
- They can be activated through T cell-dependent or T cell-independent pathways.
- They have a complex relationship with cancer, sometimes inhibiting tumor development and other times suppressing the anti-tumor response.
Structure of B cells
The structure of B cell receptors consists of four peptides, namely two light chains and two heavy chains. These chains together form two regions that are responsible for binding to antigens. Light chains are categorized as either kappa or lambda, while the heavy chains can belong to different isotypes such as IgG, IgA, IgM, IgD, or IgE.
Differences between B Cells and T Cells
|Property||B Cells||T Cells|
|Name||B lymphocytes||T lymphocytes|
|Position||Outside Lymph Node||Interior of Lymph Node|
|Membrane Receptor||BCR (Immunoglobulin) for antigen||TCR for antigen|
|Connections||Connect to antigens on the surface of invading viruses or bacteria||Connect to viral antigens on the outside of infected cells|
|Tissue Distribution||Germinal centers of lymph nodes, spleen, gut, respiratory tract; also, subcapsular and medullary cords of lymph nodes||Parafollicular areas of cortex in lymph nodes, periarteriolar in spleen|
|Surface Antibodies||Present||Absence of surface antibodies|
|Secretion||Secrete antibodies||Secrete Lymphokines|
|Function||Form humoral or antibody-mediated immune system (AMI)||Form cell-mediated immune system (CMI)|
|Blood||20% of lymphocytes||80% of lymphocytes; CD4 > CD8|
|Formation||Form plasma cells and memory cells||Form killer, helper, and suppressor cells|
|Movement to Infection Site||Plasma cells do not move to the site of infection||Lymphoblasts move to the site of infection|
|Reactivity against Transplants and Cancer Cells||Plasma cells do not react against transplants and cancer cells||Killer cells react against transplants and cancer cells|
|Inhibitory Effect on Immune System||Plasma cells have no inhibitory effect on the immune system||Suppressor cells inhibit the immune system|
|Pathogen Defense||Defend against viruses and bacteria that enter the blood and lymph||Defend against pathogens including protists and fungi that enter the cells|
Similarities between B Cells and T Cells
- Both originate in the bone marrow.
- Both are involved in adaptive immunity.
- Both are a type of lymphocytes.
- Both are nucleated and motile cells.
- Both protect the body’s immune system and help fight infections.
- Both are non-phagocytic cells.
- Both are part of the lymphatic system.
- Both are responsible for recognizing various pathogenic antigens.
- Both play a crucial role in the immune response.
Frequently Asked Questions
Q: What are T cells and B cells?
A: These are, types of lymphocytes, play vital roles in the immune system. T cells perform cell-mediated immunity, while B cells participate in humoral immunity.
Q: Where do they originate?
A: They originate in the bone marrow, with T cells maturing in the thymus and B cells maturing in the bone marrow.
Q: What is the main function of T cells?
A: T cells have diverse functions, including coordinating immune responses, activating cytotoxic T cells, and regulating immune responses through suppressor T cells.
Q: What is the main function of B cells?
A: B cells produce antibodies, recognizing and neutralizing specific pathogens, and contributing to the humoral immune response by generating antibodies and differentiating into plasma and memory cells.
Q: How do T cells and B cells recognize antigens?
A: T cells recognize antigens using T cell receptors (TCRs), while B cells utilize B cell receptors (BCRs) on their surface to bind antigens.
Q: Can T cells and B cells activate each other?
A: Certainly, they interact and activate one another. Helper T cells stimulate B cell activation by recognizing antigens presented by B cells, and activated B cells can in turn stimulate helper T cells and other immune cells.
Q: Can B cells and T cells target cancer cells?
A: Yes, both can target cancer cells. B cells produce antibodies that can attack cancer cells or oncogenic viruses, impeding tumor growth. Cytotoxic T cells directly recognize and kill cancer cells.
Q: Can B cells and T cells cause autoimmune diseases?
A: In some cases, malfunctioning of these cells can contribute to autoimmune diseases. Autoimmune diseases occur when the immune system mistakenly attacks healthy cells and tissues. Regulatory T cells help maintain immune tolerance to prevent autoimmune responses.
Q: Can B cells and T cells be used in immunotherapies?
A: Absolutely, Both are employed in various immunotherapies. Checkpoint inhibitors enhance the immune response against cancer cells by targeting specific molecules on T cells. CAR T-cell therapy involves genetically engineering T cells to express receptors that target specific cancer cells.
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