DENDRITIC CELL: TYPES, FUNCTIONS AND HISTOLOGY - BIOLOGY - 2025

The dendritic cells are a heterogeneous group of hematopoietic cells, which play an important role in innate immunity and adaptive immunity. They are cells that are responsible for detecting, phagocytizing and presenting toxins or pathogens (antigens) that enter the body.

Dendritic cells perform their function very efficiently, which is why they are known as professional antigen presenting cells. Its functions are not only important as a defense barrier in the innate immune system, but also as a link for the activation of the adaptive immune response mediated by antibodies.

Section of the skin showing a large number of dendritic cells (Langerhans) in the epidermis.

In order to fulfill their function properly, these cells must be able to discriminate between the body's own molecules and foreign molecules, in order to maintain self-tolerance. Dendritic cells guide the specificity, magnitude, and polarity of immune responses.

Due to its role in the immune system, there is great interest in exploiting its properties to develop immunotherapies against cancer, chronic infections and autoimmune diseases, as well as for the induction of tolerance to transplantation.

Types of dendritic cells

Langerhans cells

Langerhans cells are the dendritic cells of the skin. They are usually found in stratified epithelia and constitute approximately 4% of epidermal cells where they fulfill their primary defense function. Inside they have granules called Birbeck.

They were first described by Paul Langerhans in 1868 and were thought to belong to the nervous system, due to their star shape. They were later classified as macrophages and are the only type of epidermal cell with characteristics of cells of the immune system.

Interdigitating dendritic cells are widely distributed throughout the body and have a high degree of maturation, which makes them very effective for the activation of naive T lymphocytes. They are most often found in the secondary lymphoid organs, where they exert their function of activating lymphocytes.

Anatomically, they have characteristic folds in their cell membrane, which has co-stimulating molecules; they do not have granules.

However, they are essential in the presentation of viral antigens, which are subsequently presented to a type of lymphocyte called CD4 T.

Follicular dendritic cells

Follicular dendritic cells are distributed among the lymphatic follicles of the secondary lymphoid organs. Although morphologically similar to other dendritic cells, these cells do not share a common origin.

Follicular dendritic cells do not come from the bone marrow, but from the stroma and mesenchyme. In humans, these cells are found in the spleen and lymph nodes where they meet with other cells called B lymphocytes to present antigen to them and initiate an adaptive immune response.

Interstitial dendritic cells

Interstitial dendritic cells are located around vessels and are present in most organs, except the brain. Dendritic cells that are present in lymph nodes include interstitial, interdigitating, and epithelial cells.

Dendritic cells are characterized by being highly efficient antigen presenting cells, which is why they are capable of activating different cells that activate the adaptive immune response and, consequently, the production of antibodies.

These cells present antigens to T lymphocytes when they are found in the lymph nodes.

Plasmacytoid dendritic cells

Plasmacytoid dendritic cells are a specialized subset of dendritic cells characterized by detecting antigens from viruses and bacteria, and by releasing many type I interferon molecules, in response to infection.

An important role for these cells in inflammatory responses caused by activation of effector T cells, cytotoxic T cells, and other dendritic cells has been suggested.

In contrast, another group of plasmacytoid dendritic cells participates in the suppression of inflammation as a regulatory mechanism.

Veiled cells

The veiled cells of the afferent lymph are classified with the dendritic cells on the basis of their morphology, surface markers, staining, and cytochemical function.

These cells phagocytose pathogens and carry antigens from peripheral tissues to the paracortical areas in the lymph nodes. Studies suggest that these veiled cells are involved in antigen presentation in inflammatory and autoimmune diseases.

Features

Depending on their location, dendritic cells have morphological and functional differences. However, all dendritic cells constitutively express high levels of molecules called MHC-II and B7 (co-stimulator).

Having these molecules on their cell surface makes dendritic cells better antigen-presenting cells than macrophages and B cells, which require activation before functioning as antigen-presenting cells.

In general, the functions of dendritic cells are:

- Detection of the pathogen (or antigen).

- Phagocytosis (or endocytosis) of the antigen.

- Intracellular degradation of the antigen.

- Migration of the dendritic cell towards the blood or lymph.

- Presentation of the antigen to lymphocytes, in secondary lymphoid organs.

Histology

Histologically, dendritic cells are initially found in the outer areas of the skin and other organs where there is greater exposure to foreign agents. Dendritic cells are considered to have an immature phenotype with a high capacity for antigen detection and internalization.

The dendritic cells then migrate to other tissues, such as the secondary lymphoid organs, where they meet another group of cells that are very important in the immune system. These latter cells are the lymphocytes in charge of defense in the adaptive immune system.

When dendritic cells present the antigen to lymphocytes, their cellular structure changes again and acquires a mature state, in which they begin to express other different proteins on their surface.

These proteins have the function of stimulating the lymphocytes that are receiving the antigen signal, in such a way as to make them more efficient in their ability to eliminate the peptide.

Thus, as dendritic cells mature, they change histologically and structurally. It is a cycle in which the innate immune response is united with the adaptive one and occurs thanks to the detection, degradation and antigen presentation function performed by these cells.

References

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