The key difference between endogenous and exogenous antigens is that the endogenous antigen is generated within the cells while the exogenous antigen enters the body from the outside.
Antigen is a molecule or a substance that reacts to a product of a specific immune response and stimulates antibody generation. Antigenicity of that particular molecule is the ability of an antigen to induce antibody production. Also, antigens can be either a protein or a polysaccharide. Furthermore, antigen-presenting cells (APCs), such as dendritic cells mediate the processes of antigen uptake, antigen processing, and antigen presentation. Moreover, depending on the immune activity, antigens can be classified as immunogens, tolerogens, or allergens. Besides, we can also classify antigens according to their origin as exogenous or endogenous.
CONTENTS
1. Overview and Key Difference
2. What are Endogenous Antigens
3. What are Exogenous Antigens
4. Similarities Between Endogenous and Exogenous Antigens
5. Side by Side Comparison – Endogenous vs Exogenous Antigens in Tabular Form
6. Summary
What are Endogenous Antigens?
Endogenous antigens originate within the cells due to normal cell metabolism or due to an intracellular bacterial or viral infection. They can be found within the cytoplasm of APCs as self- cell proteins that linked covalently to ubiquitin. Hence, they do not require active phagocytosis. Once the antigen-processing pathways initiated, endogenous antigen degradation occurs, and peptide generation occurs by proteases. Then, these peptides make a complex with MHC class I molecules on the cell surface and present to the immune cells.
Figure 01: Antigens
Thus, followed by the recognition,the Cytotoxic T cells begin to secrete compounds that cause lysis or apoptosis of infected cells. Some examples for endogenous antigens include self-antigens, tumour antigens, alloantigens, and some viral antigens where the viruses are able to integrate proviral DNA into the host’s genome.
What are Exogenous Antigens?
The vast majority of antigens are exogenous antigens. Hence, they enter the body from the outside via various infectious agents such as bacteria, viruses, fungi, protozoa, helminths etc., or environmental substances such as dust mites, foodstuff, pollen etc., by inhalation, ingestion, or injection.
Figure 02: Exogenous Antigens
Also, APCs can actively intake exogenous antigens by endocytosis or phagocytosis and process into fragments in order to initiate the antigen-processing pathways. After initiating the pathway, the fragments present on the membrane together with MHC class II molecules and then allow recognizing by TH cells.
What are the Similarities Between Endogenous and Exogenous Antigens?
- Endogenous and Exogenous Antigens are antigens which can induce the formation of antibodies and activate the immune system.
- Also, both bind to antibodies.
- Furthermore, both cause immune responses.
- In addition, they can be proteins, peptides or polysaccharides.
What is the Difference Between Endogenous and Exogenous Antigens?
Antigen is a molecule that can bind with an antibody and cause an immune response. Also, there are two types of antigens. Namely, they are endogenous and exogenous antigens. The key difference between endogenous and exogenous antigens is that the endogenous antigens generate within the cells while the exogenous antigens come from the outside of the body. Hence, endogenous antigens are intracellular while exogenous antigens are extracellular. Moreover, exogenous antigens are the most common type of antigens while endogenous antigens are comparatively not.
The below infographic shows more details on the difference between endogenous and exogenous antigens.
Summary – Endogenous vs Exogenous Antigens
Antigens can generate within the cells or enter form the outside. Accordingly, there are two types of antigens namely endogenous antigens and exogenous antigens respectively. However, the most common type of antigen is the exogenous antigens. Endogenous antigens generate due to cell metabolism or viral or intracellular bacterial infection. On the other hand, exogenous antigens enter our body via inhalation, ingestion, or injection. Thus, this is the difference between endogenous and exogenous antigens.