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Professional and non-professional antigen-presenting cells: what are the surprising differences between them?
In the immune system, antigen-presenting cells (APCs) play a crucial role. These cells drive adaptive immune responses by initiating T cell responses by displaying antigens that bind to the major histocompatibility complex (MHC).
Antigen presentation is a key process for initiating T cells, whether targeting endogenous or exogenous pathogens, APCs are essential.
The operation of the entire immune system relies on several types of professional cells, including dendritic cells, macrophages, and B cells. These specialized APCs are able to efficiently endocytose antigens, process and display them. Relatively speaking, all cells are capable of some form of antigen presentation, but only professional APCs can effectively activate T cells.
Professional antigen-presenting cells
Professional antigen-presenting cells are characterized by expression of MHC II molecules and costimulatory molecules. These cells include dendritic cells, macrophages, and B cells, which recognize and directly stimulate T cells.
Dendritic cells
Dendritic cells are well known for their extensive role in antigen presentation. These cells are responsible for presenting foreign antigens to T cells in the form of MHC II and can also cross-present foreign antigens to cytotoxic T cells in the form of MHC I. Dendritic cells also play an important role in immune tolerance.
Macrophages
After receiving interferon secreted by T cells, macrophages can express MHC II and other costimulatory molecules, thereby displaying the phagocytized antigen fragments to T cells. Not only are they APCs, they also play a crucial role in pathological conditions due to their ability to phagocytose foreign pathogens.
B cells
B cells use their B cell receptors to directly recognize and internalize soluble antigens, and present the processed antigens to helper T cells in the form of MHC II. B cell responses are not limited to antigen presentation, but also include antibody production and memory cell formation.
Non-professional antigen-presenting cells
Compared to professional APCs, all nucleated cells can be regarded as non-professional antigen-presenting cells. They mainly utilize MHC I to display endogenous peptides and can interact with cytotoxic T cells. However, non-professional APCs generally do not express MHC II, and there are fewer circumstances that prompt them to demonstrate competence.
These non-professional APCs may also express MHC II when cells such as endothelial and epithelial cells are induced under specific circumstances, but in most cases fail to activate naive CD4+ T cells.
Interaction of antigen presentation
After dendritic cells engulf pathogens, they usually migrate to lymph nodes, where they interact with T cells. Mature dendritic cells can accurately display antigens and effectively activate T cells, promoting the implementation of cellular immune responses.
Role in cancer therapy
Antigen-presenting cells also play an important role in tumor immunity. By stimulating B cells and cytotoxic T cells, APCs have an important impact on combating tumor-associated antigens. In the latest cancer therapies, scientists have begun experimenting with genetically engineered artificial antigen-presenting cells designed to activate the patient's immune system to attack malignant cells.
How profound is the difference between professional antigen-presenting cells and non-professional antigen-presenting cells? What implications does this have for our understanding of the workings of the immune system and the development of novel therapeutic strategies?
