Antigen Processing And Presentation

Antigen Processing and presentation refer to the mechanism through which the entire antigen is degraded and loaded within MHC molecules. This further impacts the display of antigen on the cell surface, also influencing T cell recognition. In this view, macrophage and dendritic cells are often viewed as professional antigen cells. 

MHC class 1 and 2 forms of processing and presentation have undergone rigorous studies. The cross-presentation ensures that dendritic cells have acquired antigens. These are done from the environment, which is extracellular. They are then presented through MHC Class 1, activating CD8- T cells. 

Antigen Presentation 

Antigen processing and presentation Slideshare has included various components of this part of immunology. Antigen-presenting cells are special cells that include macrophages, B lymphocytes, and dendritic cells that are segregated by two properties.

• One property is expressed as class II MHC molecules towards the membranes
• Delivering a costimulatory signal which is essential to activate TH- cells

The MHC is known as the Major Histocompatibility Complex, which encodes two major membrane-bound glycoproteins. Both Class I and II function as antigen recognition. Also, TH cells usually recognize antigens combined with both classes I & II molecules. 

MHC molecules usually bind spectrum antigenic peptides, derivatives of inter cellular degradation. MHC is polygenic and polymorphic that helps to recognize varied types of antigens. Hence, different classes of MHC are explained below. 

• MHC class I- These are not considered professional APCs and might be presented as intracellular antigens
• MHC class II- They can be only on APCs and are presented as extracellular like bacteria

If the virus thrives within the cell, the immunity system should respond. For this reason, disease like Malaria are difficult to detect as the pathogen thrives within human blood cells. Thus, MHC class I is usually presented as an extracellular antigen. On the contrary, MHC class II can be presented as autophagy intracellular antigens. 

The antigen presentation cells initiate the process through the internalization of antigens through phagocytosis and endocytosis. As a result, only a part which is a class II MHC molecule, is displayed through the membrane.

 The TH cell is then recognized and relates with a complex antigen class II MHC molecule. This cell is activated after the initiation of the costimulatory signal.  

Foreign protein antigen is distinguished further into smaller antigenic peptides, forming complexes of classes I and II. The protein conversion into MHC peptide fragments is named antigen processing and presentation. 

Antigen Processing 

Antigen processing and presentation kuby ppt depict that antigen processing is necessary before presenting. This includes the transformation of proteins into antigenic peptides. 

1. MHC class I molecules – Intracellular peptides are composed of protease and proteasome within cytosol, after which it is transported into the endoplasmic reticulum. These are then assembled with MHC I molecules to present on the cell surface. 
2. MHC class II molecules- The presentation of MHC class II molecules starts with the processing of exogenous antigens, which usually starts with endocytosis. Inside the cell, it is usually covered with endosomes which further acidifies and activates protease. 

This helps to break the antigen into smaller particles. At this stage, they bounded together through peptide antigen, which travels towards the cell’s surface. 

Endogenous and Exogenous Pathways

Endogenous and exogenous pathways of antigen processing and presentation ppt depict that antigen is externally produced, while cell entry occurs through endocytosis. On the other hand, presenting cells usually ingest exogenous antigens into fragments. 

The MHC molecules with peptides are transported towards the cell surface, further recognized by Th cells. As a result, the endogenous antigen develops within the cell. Thus, viral or unique proteins are manufactured by cancerous cells. The endogenous antigen is tarnished to form peptide fragments that bind together with class I MHC molecules. This complex peptide travels towards the cell membrane. 

In this view, antigens obtained from viral proteins are typically processed through an endogenous pathway. They are further presented through MHC class I molecules. 

The key differences amongst endogenous and exogenous pathways are given below.

1. The exogenous antigen usually enters from host cell within the body. Examples would include bacteria, fungi, viruses and others. 
2. The antigen of endogenous cells are created within body cells. Examples like viral proteins, tumour antigens, and others.

The exogenous and endogenous antigen are categorised based on their origins. 

Conclusion 

Antigen processing and presentation refers to the process through which protein antigen ingestion occurs. These are generally presented by APC or antigen-presenting cells. The APCs are not fully digested in peptides, after which they display on the cell surface. APC is directly linked with an antigen-presenting molecule like MHC class I & II during the process. Presentation and processing of Antigen to immunity cells is important to engage with adaptive immunity.