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13 December, 2023 by Anshul (neobio)
Have you ever pondered the complexity of the immune response and the pivotal role that CD21 plays in this intricate dance of cells and molecules? As scientists, you probably have. Understanding the part CD21 plays in B cells is essential for those in the field of immunology and biomedical research. Below we answer your pressing questions about this key molecule.
Central to our adaptive immune system, B cells or B lymphocytes stand on the front line of our defense against pathogens. They are the orchestrators of the humoral immunity, producing antibodies that recognize and neutralize invading organisms. But within this broad category, different B cell subtypes exist, each with distinct roles and characteristics. One marker that helps distinguish these subtypes is the protein CD21, predominantly found on mature B cells.
CD21, a recognized marker for B cells, plays a pivotal role in B cell activation and the formation of immunological memory. Recognizing activated products of complement 3, CD21 is instrumental in the uptake and retention of immune complexes. Its interplay with other proteins, specifically in the CD19/CD21 complex, aids in the processing and response to T cell-dependent, complement-tagged antigens.
This interplay is not a mere nicety but a necessity for memory B cells’ survival. More than that, our understanding of CD21 has allowed us to pinpoint double positive (DP) CD21+CD27+ B cells as highly proliferating memory cells. They have been of particular interest in research related to HIV and SIV infections.
CD21’s significance goes further: changes in its expression can be a marker for disease. As much as CD21 is essential in B cells’ normal function, its absence or low levels are related to various health conditions, especially autoimmune diseases.
This brief summary provides a glimpse into the vital role CD21 plays in B cells:
For those interested in visual information, refer to our infographic below that provides a snapshot of CD21’s role in B cells:
In this guide, we will journey from understanding the basic function of CD21 in B cells to exploring how changes in its expression can impact human health, hoping to bring the captivating world of CD21 to life, equipping you for your next scientific discovery.
The CD19/CD21 complex plays a crucial role in the function of B cells. The CD19/CD21 complex is not a standalone entity but functions as a B cell coreceptor, working in conjunction with other components of the immune system to enhance the B cell’s ability to respond to antigens.
The CD19/CD21 complex’s primary function is to amplify B cell activation and contribute to the processing and presentation of antigens. CD21, also known as complement receptor 2 (CR2), recognizes activated products of complement 3 and is predominantly expressed on mature B cells and follicular dendritic cells. This recognition and interaction with complement-tagged antigens enhance the B cell’s ability to respond to T cell-dependent antigens, thereby enhancing the overall immune response.
As explained by our expert, Dr. Atul K. Tandon, Founder and CEO at NeoBiotechnologies, “The CD19/CD21 complex effectively acts as the ‘eyes and ears’ of the B cell, allowing it to recognize and respond to specific immune threats more efficiently.”
The CD19/CD21 complex enhances B cell Ag receptor signaling by working synergistically with the B cell Ag receptor. When the B cell Ag receptor recognizes an antigen, it triggers a series of signaling pathways that lead to B cell activation. The simultaneous engagement of the CD19/CD21 complex with the B cell Ag receptor, particularly in response to complement-tagged antigens, amplifies these signals, leading to more rapid and efficient B cell activation.
Beyond simply enhancing B cell activation, the CD19/CD21 complex also influences B cell Ag processing. While the CD19/CD21 complex does not directly target complement-tagged antigens for processing, its signaling function indirectly influences how B cells process these antigens.
Research has shown that coengagement of the CD19/CD21 complex results in a more rapid and efficient production of antigenic peptide/class II complexes compared with B cell Ag receptor-mediated processing alone. This enhanced processing capability may be a critical factor in how the CD19/CD21 complex promotes B cell responses to T cell-dependent complement-tagged antigens in vivo.
In summary, the CD19/CD21 complex plays a pivotal role in B cell activation and Ag processing, making it a valuable focus for researchers and scientists working with CD21 B cell related studies. As we continue to delve into the fascinating world of CD21 and its role in B cells, it’s clear that understanding this complex is crucial to advancing our knowledge of the immune system.
One of the most significant aspects of CD21’s function within the B cell complex is its role in memory B cells. Memory B cells are a special type of B cell that “remembers” pathogens the immune system has encountered previously, enabling a faster and more effective response upon re-exposure. CD21, in conjunction with CD27, plays a fundamental role in the identification and function of these cells.
The identification of memory B cells has traditionally been challenging, but recent research has shown that the expression of the CD21 and CD27 surface markers can be used to define these cells. Particularly, B cells that express both CD21 and CD27, referred to as double positive (DP) CD21+CD27+ B cells, have been identified as memory B cells.
The expression of these markers on B cells varies between peripheral blood and various lymphoid tissues. For instance, DP CD21+CD27+ B cells are predominant in all lymphoid tissues except for peripheral blood and bone marrow. Their distribution and frequency in different tissues provide valuable insights into their role in the immune response.
When it comes to activation and proliferation, DP CD21+CD27+ B cells demonstrate a higher rate compared to other B cell subpopulations. They are capable of antibody production through polyclonal activation without the assistance of T cells. This ability is crucial for a rapid and effective immune response to secondary exposure to a pathogen.
Furthermore, DP CD21+CD27+ B cells are found to have higher cell turnover rates, particularly in tonsillar memory B cells compared to other tissues. This increased turnover might be indicative of the active role these cells play in the immune response.
The role of memory B cells and, by extension, the CD21+CD27+ B cells, extends to the pathogenesis of viruses such as HIV and SIV. Interestingly, the loss of memory B cells has been associated with HIV/SIV infection.
While the mechanisms behind this loss remain unclear, evidence suggests that the loss of memory B cells correlates positively with the loss of CD4+ T cells. However, the immune activation following SIV infection may also predispose memory cells to activation-induced apoptosis.
Furthermore, DP CD21+CD27+ B cells may play a significant role in HIV infection, given their high cell turnover rate and increased antibody production. Thus, understanding the function of CD21 in these memory B cells could open new avenues for research into HIV/SIV pathogenesis and potential therapeutic interventions.
In conclusion, the role of CD21 in memory B cells is essential for understanding the body’s immune response to pathogens. Whether in the context of normal immune function or in disease states such as HIV/SIV infections, CD21 serves as a critical component in the complex world of B cells. The products offered by NeoBiotechnologies can be valuable tools for researchers exploring these areas further.
One of the intriguing aspects of B cell biology is the existence of a subset of B cells, referred to as CD21 –/low B cells. These cells have been observed in healthy individuals and are primarily composed of memory B cells. Interestingly, the presence of CD21 –/low B cells in healthy individuals could be due to subclinical chronic infections such as Epstein–Barr virus (EBV), cytomegalovirus (CMV) or Helicobacter pylori. Alternatively, they may be a part of the normal immune response, as these cells have been shown to produce antibodies against immunized pathogens.
The characteristics of CD21 –/low B cells in healthy individuals include the expression of IgM and IgD, and a proportion of these cells also show switched isotypes, indicating that they have undergone somatic hypermutation and are part of the memory B cell pool. These cells also display markers indicating previous activation, analogous to classical memory B cells.
The significance of CD21 –/low B cells extends beyond healthy individuals. An increased frequency of these cells has been observed in various disease states, including HIV, hepatitis C virus (HCV), malaria infections, and various autoimmune diseases.
This increase in CD21 –/low B cells in these diseases could be due to an expansion of this B cell subset in response to chronic activation by the infective agent or autoantigen. For instance, CD21 –/low B cells in these disorders are known to produce antibodies that recognize the infecting virus/parasite.
Interestingly, the response profile of CD21 –/low B cells differs in disease states compared to healthy individuals. For example, this subset of B cells has been shown to respond poorly to single stimuli, which could potentially lead to unresponsiveness, considering that CD21 is a part of the B cell co-receptor and is considered important for B cell activation.
In conclusion, the CD21 –/low B cell subset plays an important role both in health and disease. Their presence and activation in various disease states highlight the importance of this subset in immune response and disease pathogenesis. Tools like the monoclonal and recombinant antibodies manufactured by NeoBiotechnologies can greatly aid in further research into the role and function of CD21 –/low B cells.
In our exploration of B cells and their intricate functions, CD21 has emerged as a key player. This protein, also known as complement receptor 2 (CR2), is predominantly expressed on mature B cells and follicular dendritic cells, playing a crucial role in B cell activation, proliferation, and survival.
CD21 forms part of the essential B cell coreceptor complex, CD19/CD21, which greatly enhances signaling through the B cell Ag receptor. This complex allows B cells to respond more effectively to T cell-dependent, complement-tagged antigens, thus playing a significant role in immune responses. It also influences B cell Ag processing, which is crucial for the activation and function of these cells.
Moreover, CD21 expression is a key determinant in distinguishing various subsets of B cells, such as memory B cells and CD21 –/low B cells. Memory B cells, characterized by the absence of CD21, play a pivotal role in long-term immune protection, while CD21 –/low B cells have been linked with autoimmune diseases and chronic infections.
Given the importance of CD21 in B cell function and its potential implications in various diseases, it’s no surprise that it has garnered significant interest in the scientific community. The differential expression of CD21 among B cell subsets can serve as a biomarker to identify abnormal cells in conditions like autoimmune diseases, chronic infections, and even cancer.
Furthermore, the potential of CD21 as a therapeutic target holds great promise. By modulating CD21 expression or function, it may be possible to influence B cell activity and alter the course of immune responses. This could lead to novel treatments for conditions associated with dysregulated B cell activity, such as autoimmune diseases and certain types of cancer.
However, to fully realize this potential, the need for highly specific tools like the monoclonal and recombinant antibodies provided by NeoBiotechnologies is clear. With these tools, researchers can delve deeper into the intricacies of CD21 function in B cells, opening doors to new discoveries and interventions.
As we continue to explore the complex world of B cell biology, our understanding of CD21 and its functions will undoubtedly continue to evolve. The journey may be challenging, but the potential rewards – in terms of improved diagnostics and therapeutics – make it a worthwhile endeavor.
For further information on B cell markers, you can explore the CD22 BL-CAM B cell marker and the CD20 MS4A1 B cell marker offered by NeoBiotechnologies.
