The key difference between self and non self antigens is that the antigens on the own body cells are known as self antigens while the antigens that do not originate in the own body are called non self antigens.
An antigen is any substance that induces the immune system to produce antibodies. Antigens are composed of proteins, peptides, and polysaccharides. Any foreign invaders (bacteria and viruses), chemicals, toxins, and pollens can be antigens. However, sometimes under pathological conditions, normal cellular proteins become self antigens. Based on the origin, antigens are two types as self antigens (autoantigens) and non self antigens (exogenous antigens and tumor antigens).
CONTENTS
1. Overview and Key Difference
2. What are Self Antigens
3. What are Non Self Antigens
4. Similarities – Self and Non Self Antigens
5. Self vs Non Self Antigens in Tabular Form
6. Summary – Self vs Non Self Antigens
What are Self Antigens?
Self antigens are the antigens on the own body cells. They are also called auto antigens. They are usually cellular proteins or a complex of proteins that are mistakenly attacked by the immune system. This process leads to auto-immune diseases. Normally, a self protein becomes a self antigen because of impaired immunological tolerance. Impaired immunological tolerance can be caused due to genetic or environmental conditions. If activated cytotoxic T cells recognize these self-proteins-containing cells, then the T cells secrete various toxins to cause lysis and apoptosis. In order to keep the cytotoxic cells from killing cells containing self protein, cytotoxic cells or self-reactive T cells should be deleted. This process takes place as a result of tolerance, and it is known as negative selection. In auto-immune diseases, the associated T cells (self reactive T cells) are not deleted. Instead, these self reactive T cells attack the self protein presenting cells. Examples of auto-immune diseases are celiac disease, Grave’s disease, inflammatory bowel disease, multiple sclerosis, rheumatoid arthritis, and systematic lupus erythematosus.
Moreover, self antigens are particularly important in blood transfusion. This is because some important self antigens are present in blood cells that play a vital role in blood transfusion. A person can only receive a blood transfusion from a donor with the same type of antigens. Otherwise, the immune system will attack the donated blood.
What are Non Self Antigens?
Non self antigens are the antigens that do not originate in the own body. They are also called exogenous antigens. These antigens enter the body from outside via ingestion, inhalation, or injection. Therefore, they are termed as exogenous. These non self antigens can be pathogens (bacteria, virus, and fungi), chemicals, toxins, allergens, and pollens.
Figure 01: Non Self Antigens
Through endocytosis or phagocytosis, exogenous antigens are taken into the Antigen-presenting cells (APC). Later, these antigens are processed into fragments. APCs then present the fragments to T helper cells (CD4+) with the use of MHC class II molecules on their surface. After this, CD4+ cells become activated and start to secrete cytokines. Cytokines are substances that activate cytotoxic T cells (CD8+), antibody-secreting B cells, macrophages, and other particles.
What are the Similarities Between Self and Non Self Antigens?
- Self and non self antigens are two types of antigen molecules.
- Both antigens can trigger the immune system.
- Cytotoxic T cells (CD+) can be activated because of both antigen types.
- Both antigen types can be proteins.
What is the Difference Between Self and Non Self Antigens?
The antigens on the own body cells are known as self antigens, while the antigens that do not originate in the own body are called as non self antigens. Thus, this is the key difference between self and non self antigens. Furthermore, self antigens are cellular proteins or a complex of proteins, while non self antigens are pathogens (bacteria, virus, and fungi), chemicals, toxins, allergens, and pollens, etc.
The below infographic presents the differences between self and non self antigens in tabular form for side by side comparison.
Summary – Self vs Non Self Antigens
In immunology, an antigen is a molecule that can bind to a specific antibody or T cell receptor. The presence of these antigens in the body can trigger an immune response. Self and non self antigens are two types of antigen molecules. The antigens on the own body cells are known as self antigens, while the antigens that do not originate in the own body are called as non self antigens. So, this is the summary of the difference between self and non self antigens.
Reference:
1. “Self Antigens.” Springer.
2. “Exogenous Antigen.” Biology Articles, Tutorials & Dictionary Online.
Image Courtesy:
1. “Fimmu-11-579250-g004” By Katie L. Flanagan, Emma Best, Nigel W. Crawford, Michelle Giles, Archana Koirala, Kristine Macartney, Fiona Russell, Benjamin W. Teh, and Sophie CH Wen, on behalf of the Australasian Society for Infectious Diseases (ASID) Vaccination Special Interest group (VACSIG) – Flanagan KL, Best E, Crawford NW, Giles M, Koirala A, Macartney K, Russell F, Teh BW and Wen SCH (2020) Progress and Pitfalls in the Quest for Effective SARS-CoV-2 (COVID-19) Vaccines. Front. Immunol. 11:579250.https://doi.org/10.3389/fimmu.2020.579250 (CC BY 4.0) via Commons Wikimedia