Main Difference – Humoral Immunity vs Cell mediated immunity
Humoral immunity and cell mediated immunity are two types of adaptive immunity. Adaptive immunity generates an antigen-specific immune response. During adaptive immunity, the antigen is first recognized through receptors of the lymphocytes, and immune cell clones are produced to attack that particular antigen. Humoral immunity is triggered by B cells while cell mediated immunity is triggered by T cells. The main difference between humoral and cell mediated immunity is that antigen-specific antibodies are produced in humoral immunity whereas antibodies are not produced in cell mediated immunity. Instead, T cells destroy the infected cells by inducing apoptosis.
Key Areas Covered
1. What is Humoral Immunity
– Definition, Characteristics, How it Acts
2. What is Cell Mediated Immunity
– Definition, Characteristics, How it Acts
3. What are the Similarities Between Humoral and Cell Mediated Immunity
– Outline of Common Features
4. What is the Difference Between Humoral and Cell Mediated Immunity
– Comparison of Key Differences
Key Terms: Antibodies, Cell mediated immunity, Cytotoxic T cells, Extracellular Pathogens, Helper T Cells, Humoral Immunity, Intracellular Pathogens, Opsonization, Phagocytosis, Plasma B Cells
What is Humoral Immunity
Humoral immunity is the immunity generated by circulating antibodies. It is a component of adaptive immunity, which generates specific immune responses to a particular foreign material. The extracellular spaces of the body are protected by humoral immunity. Most pathogens that invade the body multiply in the extracellular spaces. Intracellular pathogens move from one cell to another through the extracellular space. Therefore, extracellular space is an important place to destroy pathogens. Antibodies are produced and secreted by plasma B cells. Typically, the activation of B cells occurs in T helper cells.
Figure 1: Opsonization
Antibodies destroy pathogens in three ways. They bind to the specific molecules on the surface of the pathogen, neutralizing the pathogen. This neutralization prevents the entering of the pathogen to the cells. It is also important to prevent bacterial toxins. The antibody-caught pathogens are subjected to phagocytosis by macrophages and other cells. This process is called opsonization. The binding of antibodies to the pathogens activates the complement system. The complement proteins bind to the antibody-bound pathogens and recruit phagocytic cells. The opsonization is shown in figure 1.
What is Cell Mediated Immunity
Cell mediated immunity is the immunity mediated by antigen-specific T cells. T cells are produced in the bone marrow and are matured in the thymus. After they enter the bloodstream, T cells occur can be found in the blood as well as in lymphoid tissue. The antigens should be presented on the surface of the antigen-presenting cells (APCs) along with the major histocompatibility complexes (MHC). Once T cells encounter an antigen, they proliferate and differentiate into armed effector cells. The cytotoxic T cells destroy the infected cells by inducing apoptosis. T helper cells stimulate plasma B cells to produce antibodies.
Figure 2: Cell Mediated Immunity
The IgG and IgM are the main two types of antibodies produced by T helper cells in response to plasma B cells. The memory T cells are differentiated T cells, but their action requires the activation by the specific antigen. The major characteristic feature of the cell mediated immunity is that it destroys intracellular pathogens. The cell mediated immunity is shown in figure 2.
Similarities Between Humoral Immunity and Cell Mediated Immunity
- Humoral immunity and cell mediated immunity are two types of adaptive immunity.
- Both humoral immunity and cell mediated immunity produce a specific immune response to a particular pathogen.
Difference Between Humoral and Cell Mediated Immunity
Definition
Humoral Immunity: Humoral immunity refers to a component of the adaptive immunity where B cells secrete antibodies, which circulate in the blood as a soluble protein.
Cell Mediated Immunity: Cell mediated immunity refers to the other component of the adaptive immunity, which is mediated by the activated, antigen-specific T cells.
Main Cells
Humoral Immunity: The humoral immunity is mediated by B cells.
Cell Mediated Immunity: The cell mediated immunity is mediated by T cells.
Cell Types
Humoral Immunity: Humoral immunity is mediated by T cells, B cells, and macrophages.
Cell Mediated Immunity: Cell mediated immunity is mediated by helper T cells, cytotoxic T cells, natural killer cells, and macrophages.
Action
Humoral Immunity: The humoral immunity acts on the extracellular microbes and their toxins.
Cell Mediated Immunity: The cell mediated immunity acts on intracellular microbes such as viruses, bacteria, and parasites and tumor cells.
Receptors
Humoral Immunity: The BCR receptors are involved in the humoral immunity.
Cell Mediated Immunity: The TCR receptors are involved in the cell mediated immunity.
Accessory Surface Molecules
Humoral Immunity: The Igα, Igβ, CD40, CD21, and Fc receptors are the accessory receptors of the humoral immunity.
Cell Mediated Immunity: The CD2, CD3, CD4, CD8, CD28, and integrins are the accessory receptors of the cell mediated immunity.
Role of MHC Molecules
Humoral Immunity: The unprocessed antigens are recognized by the humoral immunity.
Cell Mediated Immunity: The antigens are processed and presented by MHC complexes in the cell mediated immunity.
Secretion
Humoral Immunity: The plasma B cells secrete antibodies in the humoral immunity.
Cell Mediated Immunity: The T cells secrete cytokines.
Onset
Humoral Immunity: The humoral immune response is rapid.
Cell Mediated Immunity: The cell-mediated immune response is a delayed type of hypersensitivity.
Tumor Cells and Transplants
Humoral Immunity: The humoral immunity does not act on the tumor cells and transplants.
Cell Mediated Immunity: The cell mediated immunity acts on tumor cells and transplants.
Conclusion
Humoral immunity and cell mediated immunity are two types of adaptive immunity in which a specific immune response is produced for a particular pathogen. Antibodies are produced by the plasma T cells in the humoral immunity. In cell mediated immunity, T cells induce the apoptosis of the infected cells. Humoral immunity destroys the extracellular pathogens whereas cell mediated immunity destroys the intracellular pathogens. This is the difference between humoral and cell mediated immunity.
Reference:
1. Janeway, Charles A, and Jr. “The Humoral Immune Response.” Immunobiology: The Immune System in Health and Disease. 5th edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here. Accessed 20 Sept. 2017.
2. “Cell mediated immunity.” Wikipedia, Wikimedia Foundation, 31 Aug. 2017, Available here. Accessed 20 Sept. 2017.
Image Courtesy:
1. “Opsonin” By GrahamColm at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “2218 Clonal Selection and Expansion of T Lymphocytes” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
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