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Self-Antigens vs. Non-Self Antigens: Examples & Cluster of Differentiation Markers

December 2021

Antigens are molecules present on the surface of cells that bind to receptors on antibodies or on the surface of lymphocytes. Antigens are classified based on where they originate, and the immune system discriminates between native and foreign antigens in order to fight against pathogens. Immunology research utilizes the binding properties of antigens with antibodies in order to detect, track, and isolate specific cell populations within blood samples.

Self vs Non-Self Antigens

There are three types of antigens, described by where they originate. Autoantigens are produced in the body’s own cells; endogenous antigens are produced in bacteria or viruses living within the body; exogenous antigens are produced outside the body and are foreign to the immune system. Autoantigens are known as “self-antigens,” while endogenous and exogenous antigens are known as “non-self” antigens.

Self-Antigen Examples

Self-antigens present on the surface of leucocytes (which include lymphocytes such as B or T cells) are also known as “clusters of differentiation.” A cluster of differentiation [CD] on a B or T cell can serve as a cellular marker that identifies the cell to the rest of the body. Clusters of differentiation can also serve as receptors or ligands (which activate receptors on other cells) to facilitate cell signaling, which allows the cell expressing the CD to influence or manipulate the behavior of other cells in the body. CDs also serve in the body’s adaptive immune response, signaling B cells to produce antibodies that can bind to specific non-self-antigens on the surface of pathogens, or signaling T cells or other macrophages to coordinate attacks on hostile foreign cells.

Clusters of differentiation self-antigens are described in terms of the antibodies or cellular receptors to which they bind. Immunologists commonly refer to a cluster of differentiation lists in order to identify lymphocytes and the roles they play in the immune system. For example, helper T cells, which release cell-signaling cytokines when activated, are known as “CD4+ cells,” and killer T cells, which directly attack pathogens by secreting cytotoxins, are described as “CD8+ cells.”

The body ensures that self-antigens don’t trigger an immune response through a process known as “central tolerance” during the development of B and T Cells. Through central tolerance, or “negative selection,” lymphocytes with antigen-binding sites that might bind to and become activated by self-antigens are eliminated during cellular development. In this way, only lymphocytes that are unreactive with self-antigens (that is, only B or T cells that only react with non-self-antigens) reach maturity and participate in the immune system.

Non-Self Antigen Examples

Non-self-antigens include the antigen structures found on the surfaces of foreign bacteria, viruses, fungi, parasites, or other non-native biocompounds. The immune system relies on antibody-antigen binding and the binding of antigens with receptors on B or T Cells to recognize non-self-antigens within the body. The binding of non-self-antigens to antibodies or lymphocytes often triggers an immune response, which can result in neutralizing the pathogenic cell presenting the non-self-antigen, or flagging the non-self-antigens to be recognized by other elements of the immune system.

Antigens in Immunology Research

Scientists can introduce antibodies capable of binding to specific clusters of differentiation in order to track those cells for analysis or to manipulate their behavior, similar to how the immune system deploys antibodies to flag the non-self-antigens of the surface of foreign cells.

For example, antigen-based vaccines train the immune system to fight pathogens by introducing specific non-self-antigens to a patient in order to activate B cells to produce antibodies that can fight or flag the pathogen-in-question in the event of future infection. Or in a research setting, utilizing the exclusive binding properties of the antibody-antigen coupling, specific cells within a heterogenous cell population can be targeted, identified, marked, and even separated from the rest of the sample.

Antigens and Buoyancy Activated Cell Sorting with Biotinylated Antibodies and Streptavidin Microbubbles

The antibody-antigen reaction lends itself well to applications in cell sorting procedures, in which target cells sub-types are isolated to create a high-purity population of heathy cells that can be studied or used in downstream research. In fact, Akadeum Life Sciences has developed a breakthrough cell sorting technique called Buoyancy Activated Cell Sorting [BACS] that utilizes the antibody-antigen reaction to conduct cell separation protocols gently and efficiently.

BACS begins with identifying the antigen features present on the surface of unwanted cells in a sample. Then, biotinylated antibodies with receptors that correspond to the antigens on the unwanted target cells are mixed into the sample. These antibodies bind to the specific antigens on the surface of the target cells, essentially “labeling” them for removal. Next, solid buoyant particles, “microbubbles”, coated with streptavidin protein are mixed into the sample. The streptavidin on the microbubbles binds with the biotin in the biotinylated antibodies bound to the antigens on target cells through a mechanism called the streptavidin-biotin complex. The bonds of the streptavidin-biotin complex feature a strong affinity that allows the unwanted target cells to adhere strongly to the microbubbles. The microbubbles and their captured cells then float gently to the surface of the sample, where they can be removed easily. Once the target cells have been removed, what remains is an enriched population of viable cells, ready for analysis or downstream processing.

For example, BACS can be employed in T cell isolation to derive a healthy population of T cells to study how they function during an immune response. Binding the biotinylated antibodies to the antigens on the surface of unwanted cells, and subsequently removing those cells from the sample with streptavidin-coated microbubbles leaves T cells untouched, allowing researchers to isolate T cells immunotherapy research.

While traditional methods of cell separation subject samples to intense mechanical or magnetic forces and require expensive equipment to conduct, Akadeum’s BACS kits are gentle, cost-effective, and easy to use. Moreover, the BACS technique delivers accurate, scalable cell isolation for small labs and large research institutions alike. Check out Akadeum’s products page to learn more about how to isolate T cells with BACS to study pathogens with non-self-antigens.

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