Dendritic Cells- Definition, Structure, Immunity, Types, Functions


The immune system is a complex network of cells and molecules that protect the body from infections and diseases. The immune system can be divided into two main branches: the innate immune system and the adaptive immune system. The innate immune system is the first line of defense that responds quickly and non-specifically to any foreign substance or pathogen. The adaptive immune system is the second line of defense that responds slowly but specifically and memorably to a particular antigen.

An antigen is any substance that can trigger an immune response. Antigens can be derived from bacteria, viruses, fungi, parasites, toxins, or even self-cells. However, not all antigens can directly activate the adaptive immune system. Most antigens need to be processed and presented by specialized cells called antigen-presenting cells (APCs). APCs are cells that can capture, process, and display antigens on their surface in association with molecules called major histocompatibility complex (MHC). MHC molecules are proteins that bind to antigens and present them to T cells, which are a type of white blood cell that can recognize and respond to specific antigens.

There are different types of APCs in the immune system, such as macrophages, B cells, and dendritic cells. Among them, dendritic cells are considered to be the most potent and efficient APCs. Dendritic cells are named after their distinctive shape, which resembles the branching projections of nerve cells called dendrites. Dendritic cells are widely distributed in various tissues of the body, especially those that are exposed to the external environment, such as the skin, mucous membranes, lungs, and intestines. Dendritic cells act as sentinels that constantly patrol for invading pathogens and capture them by various receptors on their surface. Once they encounter an antigen, they undergo a process of maturation and migration to the lymph nodes, where they present the antigen to T cells and initiate an adaptive immune response.

Dendritic cells play a crucial role in bridging the innate and adaptive immune systems. They not only present antigens to T cells but also provide additional signals that determine the type and magnitude of the immune response. Dendritic cells can also activate other types of immune cells, such as B cells and natural killer (NK) cells. Furthermore, dendritic cells can modulate the balance between immunity and tolerance by regulating the function of regulatory T cells, which are a subset of T cells that can suppress excessive or harmful immune responses.

Dendritic cells are a heterogeneous group of cells that consist of multiple subsets with different origins, phenotypes, functions, and locations. The classification and nomenclature of dendritic cell subsets are still evolving and vary among different species. However, some common subsets of dendritic cells include plasmacytoid dendritic cells (pDCs), conventional dendritic cells (cDCs), migratory dendritic cells (mDCs), and monocyte-derived dendritic cells (moDCs). Each subset of dendritic cells has distinct roles in immunity and inflammation.

In this article, we will discuss the structure, immunity, types, and functions of dendritic cells in detail. We will also explore how dendritic cells interact with other immune cells and how they contribute to various diseases and disorders.