Immunogenetics: Open Access
Open Access

Human Leukocyte Antigens and the Immune System's role in Self-Recognition

Jessica Rozengurt^{* *}Correspondence: Jessica Rozengurt, Department of Pathology, University of California, Los Angeles, California, USA, Email:

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Description

The immune system's ability to differentiate between the body’s own cells (self) and foreign invaders (non-self) is essential for maintaining health and preventing disease. A component of this process is Human Leukocyte Antigens (HLAs), which are key molecules involved in immune recognition. HLAs are a diverse group of proteins found on the surface of cells and they help the immune system identify and respond to infections, as well as protect against potentially harmful agents. By presenting fragments of proteins (antigens) from within or outside of cells, HLAs enable immune cells to distinguish self from non-self, which is important in preventing autoimmune diseases. This essay explores the function of HLAs in immune recognition, their role in self-tolerance and their importance in maintaining the delicate balance between immunity and autoimmunity.

HLAs are part of the Major Histocompatibility Complex (MHC), a collection of genes that code for proteins responsible for antigen presentation. These molecules serve different purposes but share a common goal: Enabling the immune system to monitor and respond to both internal and external threats.

Class I HLAs are present endogenous antigens, which are fragments of proteins produced inside the cell. These proteins could be normal cellular components or fragments of proteins from invading pathogens, such as viruses. When a cell becomes infected with a virus, for example, viral proteins are processed and displayed on the cell surface by Class I HLAs. This allows cytotoxic T cells (CD8⁺ T cells) to recognize infected cells and initiate their destruction, preventing the spread of the infection.

Class II HLAs, on the other hand, are primarily found on specialized immune cells known as Antigen Presenting Cells (APCs), such as dendritic cells, macrophages and B cells. These cells take up foreign particles, such as bacteria or viruses and process them internally. The resulting antigens are displayed on Class II HLAs on the cell surface. This interaction allows helper T cells (CD4⁺ T cells) to recognize the foreign antigens and trigger a broader immune response. Helper T cells activate other immune cells, including B cells to produce antibodies and cytotoxic T cells to eliminate infected cells. This system ensures that the immune response is well-coordinated and effective against a range of pathogens.

One of the unique features of HLAs is their genetic diversity. The HLA genes are highly polymorphic, meaning that different individuals have different variants of these genes. This diversity is examining for the immune system’s ability to recognize a wide array of potential pathogens. Each person inherits a combination of HLA alleles from their parents and this genetic variation enhances the population’s ability to mount effective immune responses against diverse threats. This diversity also explains why organ transplantation can be challenging, as a mismatch in HLA types between a donor and recipient can lead to organ rejection.

Self-recognition and immune tolerance

A vital aspect of immune system function is self-recognition the ability of the immune system to distinguish the body’s own cells from foreign invaders. This is achieved through immune tolerance, a process that prevents immune cells from attacking the body’s own tissues. If a T cell strongly recognizes and binds to a self-antigen, it is eliminated or rendered inactive through a process called negative selection. This ensures that T cells that could potentially cause autoimmune responses are removed before they can become active.

Despite these safeguards, immune tolerance can sometimes break down, leading to autoimmune diseases. These conditions occur when the immune system mistakenly targets the body’s own tissues as if they were foreign. Some autoimmune diseases, such as rheumatoid arthritis, lupus and type 1 diabetes, have been linked to specific HLA types that predispose individuals to immune dysfunction. In certain cases, environmental factors like infections or stress can trigger an autoimmune response, leading to the development of these disorders. Furthermore, the immune system’s ability to distinguish self from non-self is not always perfect. In some situations, the immune system may fail to recognize altered self-cells, leading to their persistence and uncontrolled growth. This highlights the importance of the immune system’s ongoing vigilance in recognizing and responding to both foreign invaders and abnormal self-cells.

Conclusion

Human Leukocyte Antigens (HLAs) are indispensable to the immune system’s ability to differentiate between self and non-self. Through the presentation of peptide fragments from inside and outside of cells, HLAs enable the immune system to identify and respond to infections and abnormal cells, such as cancerous cells. The genetic diversity of HLAs enhances the immune system’s capacity to defend the body against a wide range of pathogens. However, maintaining a balance between immune activation and immune tolerance is analytical, as errors in self-recognition can lead to autoimmune diseases. Analyzing the role of HLAs in immune function and self-tolerance is essential for advancing treatments for immune-related disorders and improving the success of organ transplantation. Ultimately, HLAs are central to the immune system’s intricate and precise recognition of self, ensuring protection from external threats while safeguarding the body’s own tissues.