CELLS THAT GENERATE THE IMMUNE RESPONSE IN VERTEBRATES - BIOLOGY - 2025

What are the cells responsible for generating the immune response in vertebrates? These include leukocytes, which are blood cells produced in the bone marrow. These are classified into various cells, such as phagocytes, granulocytes, and lymphocytes.

These cells integrate the innate and acquired immune systems, which are present in vertebrates. The innate system includes, among others, the killer or NK cells, mast cells, and eosinophils. The adaptive system is made up of T and B lymphocytes and antibodies.

Monocyte Source: Bobjgalindo, from Wikimedia Commons

The immune system of vertebrate animals is a complex network of cells and organs that function in coordination, defending the body against viruses, bacteria or tumor-like cells.

All immune cells work together, complementing and strengthening immune function. To achieve this synchrony, these cells communicate with each other, through secretions of a molecule called cytokine. This soluble mediator also activates cell membrane receptors.

When these cells detect an antigen, they attack and kill it. In this way they create a "memory", which is used to attack immediately if the pathogen threatens the body again.

Innate immune system

-Leukocytes

They are cells with a nucleus, which have the ability to move through pseudopods. They can leave the bloodstream where they are, through a mechanism called diapédesis. In this way they could have contact with the different tissues of the body.

Leukocytes or white blood cells originate in lymphatic tissue and bone marrow, deriving from hematopoietic stem cells. The function within the immune system is to be the executors of the immune-type response against infectious agents or foreign substances.

These cells are classified into:

Phagocytes

These cells are found in tissues and in the blood. Its function is to capture cellular debris and microorganisms, introducing them inside to eliminate them. This process is called phagocytosis.

The types of phagocytes are:

Mast cells

Mast cells, also known as mast cells, possess Toll-like receptors. These cells can destroy and engulf Gram negative bacteria, processing their antigens. In addition, they induce the inflammatory response, since they produce cytokines.

Monocytes

These cells develop in the bone marrow and reach maturity when they are in the blood. The vast majority of these leave the bloodstream, going to the different tissues and organs. When they pass through the capillary epithelium and enter the connective tissue, they become macrophages.

Macrophages

This cell is the first to identify and trap antigens. Its function is to break down these substances and present the smaller proteins to T lymphocytes.

Dendritic cells

These cells are considered the most efficient in presenting antigens, being able to interact with T lymphocytes and initiate the immune response. They are located in the lungs, nose, stomach, intestines, and on the skin.

Granulocytes

They are cells that have granules, inside which contain enzymes. They are released during conditions such as asthma and allergies, in addition to infections.

Granulocytes, also known as polymorphonuclear leukocytes, comprise three types of immune cells:

Eosinophils

These granular proteins are responsible for the vast majority of inflammatory functions, mainly those related to the origin and development of allergic diseases. They contain the enzyme histamine, responsible for the hydrolysis of histamine, thus contributing to the regulation of the allergic response.

Neutrophils

Neutrophils are the most abundant of the group of leukocytes found in the bloodstream. In the acute phase of inflammation, as part of bacterial infection, neutrophils are the first to arrive and act.

Basophils

Basophils are found in the blood and only occasionally can they accumulate in some tissues. In the case of a parasitic infection, basophils clump together in the lung mucosa, the skin, and the nasal mucosa.

From those areas of the body, they release the substances they contain in their granules. These will contribute to the inflammatory process and the elimination of the infectious agent.

Natural killer cells

This type of lymphocyte, also known as NK cells, does not directly attack invading agents. They destroy cells that are infected, recognizing them by low levels of MHC antigens. This condition is called "lack of identity" due to low levels of MHC antigens.

Normal cells are not attacked because their MHC antigens are not altered.

Adaptive immune system

-Lymphocytes

Lymphocytes are special types of white blood cells that are derived from hematopoietic stem cells, located in the bone marrow. There are two types: T and B lymphocytes.

T lymphocytes

These play a very important role in the cell-mediated immune response. T cells recognize a pathogen, after it has been processed by the histocompatibility complex (MHC) molecule.

There are several types of T lymphocytes, among which are:

Auxiliaries

Helper T cells contribute to other white blood cells in immunological processes, thus regulating immune-type responses in the innate and adaptive systems. The cytokine signals they produce increase the activity of killer T cells, in addition to activating the microbicidal function of macrophages.

Auxiliary lymphocytes do not eliminate pathogens directly; their function is to control and encourage other cells to carry out these tasks.

Murderess

The cytotoxic or killer T cell attaches itself to the infectious agent, spreading over it. It then dumps the chemicals found in its gallbladder, destroying the target cell. Subsequently, the killer cells move to find and attack another tumor or infected cell.

Memory

Memory T cells are generated after a primary infection has occurred. They are in charge of mediating the body's defense against possible new infections caused by the same pathogen.

Due to this characteristic, they constitute the cornerstone of vaccines, since they keep the information of the inactive antigen to which the organism was exposed. In addition to these functions, memory T cells work against cancer cells.

Suppressor

The suppressor or regulatory T cells are in charge of closing, once the reaction has finished, the T cell-mediated immunity.

Gamma delta T cells

Gamma delta T cells can be found in tissues that are associated with the gut, skin, and lining of the lungs, where they accumulate during inflammation. Consequently, these cells are involved in immune actions against a wide range of viruses and bacteria.

T gamma delta immune cells are rare in humans, being abundant in chickens, rabbits, sheep and cattle.

B lymphocytes and antibodies

B lymphocytes are responsible for humoral immunity. Its main function is to defend the host against germs. For this, they produce antibodies that are responsible for recognizing the antigenic molecules present in pathogens.

In addition to these, B lymphocytes present antigens to T cells and participate in the regulation of the body's responses to autoantigens, and to those of an inflammatory nature.

Antibodies

Antibodies, also known as immunoglobulins, are glycoproteins that are found in blood or any other type of body fluid. These are part of the immune system, identifying and neutralizing bacteria and viruses, as well as other foreign elements that could attack the organism of vertebrates.

References

1. Prieto Martína J. Barbarroja, Escuderoab H. Barcenilla, Rodrígueza D. Díaz Martín (2013) Functions of B lymphocytes Science direct. Recovered from sciencedirect.com
2. Wikipedia (2019). Immune system. Recovered from en.wikipedia.org.
3. Mario Riera Romo, Dayana Pérez-Martínez, Camila Castillo Ferrer (2016). Innate immunity in vertebrates: an overview. NCBI. Recovered from ncbi.nlm.nih.gov.
4. Carlos Ramón Bautista Garfa (2010). Importance of γδ T lymphocytes in the immune response of bovines. Scielo. Recovered from scielo.org.mx.
5. Joana Cavaco Silva (2018). What are lymphocytes and what are healthy levels to have? Medical news today. Recovered from medicalnewstoday.com