Humoral and Cell-Mediated Immunity
Humoral immunity and cell-mediated immunity is a part of active immunity. They are
the mechanisms which protect our body against diseases when our innate immune
system fails. As a part of active immunity, they take place after a couple of days the
The Functions Include:
- Recognition of specific non-self-antigens and presence of self-antigens.
- Generate responses to eliminate specific pathogens or pathogen-infected cells.
- Development of immunological cells.
In this topic, we will further discuss humoral immunity and cell-mediated immunity
and their differences.
What is Humoral Immunity?
Humoral immune activity is one of the mechanisms of the active immune system and is associated with circulating antibodies in contrast to cellular immunity. The wide range antibody activities is a response to rapid production of antigen-specific B cells during infections which increases antibody titres with enhanced affinity for the inciting agent and more directed and effective response.
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What is Cell-Mediated Immunity?
Cell-mediated immunity is a type of adaptive immune response that does not involve antibodies but it does involve the activation of NK cell and macrophages and the production of antigen-specific cytotoxic T-lymphocytes and the release of several cytokines in response to a foreign antigen. Cell-mediated immunity plays an important role in controlling viral, chlamydia, rickettsia and protozoan infections such as trypanosomes as antibodies cannot penetrate and attack intracellular pathogens which multiply within the host cells.
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Humoral and Cell-Mediated Immune Response
The humoral immune system starts with the production of proactive antibodies against infection or reinfection by common microorganisms such as staphylococci and streptococci. B- Lymphocytes, which have specific antigen receptors react when they come to contact with the specific antigen by producing plasma cells. These plasma cells produce antigen-specific antibodies and memory cells which enable the body to rapidly produce antibodies if the same antigen appears later. The differentiation of B-cells is stimulated by interleukin-2 (IL-2) which is secreted by CD4+ T cells and foreign antigens processed by macrophages.
Antibodies which are produced by plasma B-cells are found mainly in the blood spleen and lymph nodes and they eliminate antigens in several ways. Some of them are, by activating the complement system and neutralising viruses and bacterial toxins. Another method is by coating the antigen by opsonization or forming an antigen-antibody complex to stimulate phagocytosis which promotes antigen clumping and prevents antigens from attaching to host cells.
The mechanism of cell-mediated immunity takes a different approach than humoral immunity. This mechanism protects the body through the following activities:
- The response starts by activating antigen-specific cytotoxic T-lymphocytes or CTLs which can destroy body cells which show epitopes of foreign antigen on their surfaces such as cells with intracellular bacteria, cancer cells which show tumour antigens and virus-infected cells.
- It also activates NK cells and macrophages which enable them to destroy intracellular pathogens.
- The response stimulates the cells to produce a wide range of cytokines that regulates the function of other cells involved in adaptive immune responses and innate immune responses.
Cell-mediated immunity is directed primarily towards microbes which survive phagocytes and microbes that infect non-phagocytic cells. It also plays a major role in delayed transplant rejection.
Difference between Humoral Immunity and Cell-Mediated Immunity
There are various differences between humoral immunity and cell-mediated immunity and we will discuss them below.
Cell-Mediated Immunity vs Humoral Immunity
|Characteristics||Humoral Immunity||Cell-Mediated Immunity|
|Definition||Humoral immunity is mediated by macromolecules which are found in extracellular body fluids.||This type of immunity is mediated by the T-lymphocytes, NK cells and other immune system cells of the body.|
|Mediator||B-cells are involved in humoral immunity.||T-cells are the primary mediators of Cell-mediated immunity.|
|Components||The components include macrophages, B-cells and T-cells.||The components include T cells, cytotoxic T-cells, NK cells and macrophages.|
|Pathogen||Humoral immunity protects the body against extracellular pathogens and their toxins.||Cell-mediated immunity protects the body against intracellular pathogens.|
|Pathogen recognition||Recognises pathogens in circulating in blood or lymph.||It responds to any cell that displays aberrant MHC markers which include cells invaded by pathogens, transplanted cells or tumour cells.|
|Antigen detectors||Antibodies and phagocytes are used to detect antigens.||MHC molecules on the cell surface and receptors are used to detect antigens.|
|Antigen binding||Antigens are not processed.||Antigens are processed and presented for T-Lymphocyte response.|
|Receptor involved||B-cell receptors are involved.||T-cell receptors are involved.|
|Accessory surface receptors/ molecules||Fc receptors, Igα, Igβ, , CD21, CD40||Integrins, CD3 molecular complex
Dimer of ∑ chain, CD4, CD8, CD2, CD28,
|T-cell involved||CD4+ T helper cells are involved.||CD4+ and CD8+ T cells are involved.|
|Antibodies formation||Antibodies are produced in the humoral response.||Antibodies are not formed.|
|Onset||The onset is rapid.||The onset is delayed.|
|Result||Plasma B cells are differentiated and secrete antibodies.||Cytokines are secreted.|
|Immunological surveillance||Immunological surveillance is absent.||Immunological surveillance is present.|
|Hypersensitivity reactions||Humoral immunity mediates hypersensitivity type I, II and III||Cell-mediated immunity regulates type IV hypersensitivity.|
|Role in grafting and organ transplantation||It may be involved in early graft rejection due to preformed antibodies.||Cell-mediated immunity participates in rejection of organ transplant.|
|Cancer immunity||Does not offer immunity against cancer.||Destroys cancerous and tumour cells and offers protection against cancer.|
|Assessment method||From plasma level of antibodies||Skin test for the development of a delayed type of hypersensitivity|
Similarities Humoral and Cell-Mediated Immunity
The similarities between humoral and cell-mediated immunity are:
- Both types of immunity systems are active immunities and have a lag period
- Both humoral and cell-mediated are active against several types of pathogens.
- Both immunity systems are not effective in immune-deficient individuals.
FAQ (Frequently Asked Questions)
Q: What is Active Immunity?
Ans: The immunity which results from the production of antibodies by the immune system in response to the presence of an antigen. Active immunity in a human body also takes place after immunisation. Active immunity can be classified into two categories. These are
- Natural Immunity: In this type of immunity, antibodies develop in response to an infection.
- Artificial Immunity: Antibodies are developed in response to vaccination.
Active immunity involves the production of memory cells and is usually permanent. The individual is protected from the disease throughout their life.
Q: What is the Primary Function of Humoral Immunity and Cell-Mediated Immunity?
Ans: The primary function of the humoral, or antibody-mediated, immunity is to control freely circulating pathogens. Pathogens which travel across the body through the blood and lymph are destroyed by humoral immunity. The major cells involved in this type of immunity are B-cells, CD4+ T cells and macrophages.
As for antibody-mediated immunity, it protects the body which invades cells. The cells involved in this type of immunity are T cells, cytotoxic T-cells, NK cells and macrophages.