What are plasma B cells?

Plasma B cells are specialized white blood cells derived from activated B-lymphocytes. They are essential for the body's adaptive immune system and play a critical role in humoral immunity. Upon encountering a pathogen, plasma B cells produce large quantities of antibodies specific to that pathogen, helping to neutralize and eliminate it from the body. These antibodies circulate in the bloodstream and bind to antigens on the surface of pathogens, marking them for destruction by other immune cells.

Plasma B cells can secrete hundreds to thousands of antibody molecules per second, making them powerful contributors to immune defense. In addition to antibody production, recent research suggests that plasma B cells may also play a regulatory role by inhibiting certain T-helper cell functions, helping to fine-tune the immune response. Their role in antibody production and immune regulation makes them indispensable for protecting the body from infections.

B cell development and differentiation

B cell maturation is a multi-stage process that begins in the bone marrow and continues in peripheral lymphoid tissues. The differentiation and function of B cells are controlled by a network of transcription factors and signaling pathways.

B cell maturation process

B cells undergo a complex maturation process that begins in the bone marrow and progresses through several stages until they become fully functional. In the bone marrow, early B cells start as hematopoietic stem cells and gradually differentiate into pro-B and pre-B cells.

At the pre-B cell stage, they express the pre-B cell receptor, an essential step for their survival and progression. As they mature into immature B cells, they express surface immunoglobulin (IgM), which enables them to respond to antigens. Immature B cells then migrate to the spleen and lymph nodes, where they undergo further maturation. In these secondary lymphoid tissues, they develop into mature naïve B cells, expressing both IgM and IgD on their surface. Upon encountering an antigen, they can differentiate into plasma cells or memory B cells, which are crucial for adaptive immune responses.

Transcription factors and signaling pathways

B cell development is governed by several key transcription factors and signaling pathways. Pax5 is critical for early B-cell lineage commitment, promoting B-cell-specific genes while repressing genes that lead to non-B-cell fates. E2A and EBF1 are essential for early B cell differentiation, with EBF1 driving B lineage specification and working in concert with Pax5. IRF4 and IRF8 play crucial roles in later stages, particularly in class switch recombination and somatic hypermutation, alongside cytokines IL-4 and IL-21, as well as in regulating B-cell maturation.

Signaling through the pre-B cell receptor (pre-BCR) and BCR is essential for the survival and developmental progression of B cells through their developmental stages. The NF-κB pathway is a central component, with both canonical and non-canonical pathways activated at various stages. The PI3K/AKT pathway supports cell survival and proliferation, working alongside JAK-STAT signaling, which is activated through the IL-7 receptor during early B cell development. Cytokines BAFF and APRIL are also crucial for B cell survival and maturation. This pathway is essential for the proliferation of pro-B cells and for preventing premature light-chain rearrangement.

In the pre-BCR stage, signaling is mediated through SYK, BLNK, and BTK, which are critical for initiating downstream cascades such as the MAPK/ERK pathway, which regulates cell proliferation, and the PI3K/AKT pathway, which modulates survival. The transcription factors IKAROS and AIOLOS form a negative feedback loop, ensuring appropriate signaling thresholds and preventing overactivation. FOXO1 is another important transcription factor regulated by these pathways, essential for the activation of genes like RAG1/2, which are crucial for immunoglobulin gene recombination.

Structure and characteristics of plasma cells

Plasma cells are round-to-ovoid cells measuring 14 to 20 micrometers in diameter, with a distinct appearance characterized by abundant deep blue cytoplasm and a pale perinuclear zone, representing the Golgi apparatus. They have an eccentrically placed round nucleus with a "clock face" or cartwheel arrangement of chromatin. Most plasma cells are uninucleate, although some may be binucleate or multinucleate. Cytoplasmic inclusions, such as Russell bodies, may also be present, which are dilated endoplasmic reticulum cisternae filled with condensed immunoglobulins.
Electron microscopy further reveals the presence of rough endoplasmic reticulum, cytoplasmic fibrils, and numerous mitochondria. Plasma cells also exhibit intracytoplasmic inclusions, which are either elliptical, round, or needle-like and result from the accumulation of immunoglobulins. These morphological features reflect the plasma cell's role in producing and secreting large quantities of antibodies.

Surface markers and identification of plasma cells

Plasma cells are identified by several key surface markers. In both humans and mice, plasma cells commonly express CD138 (Syndecan-1) and lack CD19. Human plasma cells are also characterized by high levels of CD38, while mouse plasma cells express additional markers such as Ly6k, Sca-1/Ly6, and CD98. For accurate and consistent detection, tools like the Human Syndecan-1 ELISA Kit (CD138)from Abcam provide reliable results, making them valuable resources in studies involving plasma cells.

Plasma cells typically show reduced or absent expression of surface immunoglobulins, including IgD, and display low levels of MHC class II molecules. Other notable markers include CD27, CXCR4, and BCMA (B cell maturation antigen), which, along with transcription factors like XBP1, IRF4, and BLIMP1, are generally expressed at high levels in plasma cells. These markers are integral to plasma cell identity and function, helping distinguish them from other B cell subsets. Unlike the low levels seen for surface immunoglobulins and MHC class II, these markers are robustly expressed, ensuring clear identification in research and diagnostics.

At Abcam, we offer anti-Syndecan-1 antibody, a rabbit recombinant monoclonal antibody suitable for IHC-P, WB, ICC/IF, and Flow Cyt (Intra), which reacts with human, mouse, and rat Syndecan-1 (CD138). The anti-CXCR4 antibody [UMB2], a rabbit recombinant monoclonal antibody suitable for IHC-P, WB, ICC/IF, IHC-Fr, and Flow Cyt (Intra), also reacts with human, mouse, rat, and transfected cell line samples.

Function of plasma B cells

Antibody production by plasma cells begins as B cells are activated by specific antigens, leading to their transformation into highly efficient, antibody-secreting plasma cells.  The importance of humoral immunity lies in its ability to defend the body against extracellular infections by mobilizing antibodies, a key component in neutralizing and eliminating pathogens.

How do plasma cells produce antibodies?

Plasma cells are the terminally differentiated form of B cells that specialize in producing and secreting large quantities of antibodies. Upon activation by an antigen and with the help of T cells, B cells proliferate and differentiate into plasma cells. These plasma cells secrete antibodies at an extremely high rate, up to 2,000 molecules per second, targeting specific antigens. Although many plasma cells die after a few days, some persist in the bone marrow, continuing antibody production for months or even years, providing long-term immunity.

Importance of humoral immunity

Humoral immunity is a crucial component of the immune system that protects against extracellular pathogens. It involves B cells producing antibodies that neutralize pathogens, prevent their entry into cells, and enhance their destruction by phagocytes through processes like opsonization. Additionally, antibodies activate the complement system, which further aids in the elimination of pathogens by recruiting immune cells and directly lysing microorganisms. This form of immunity plays a vital role in defending against infections and promoting long-lasting protection.

Lifespan and survival of plasma cells

Plasma cells, the key players in antibody production, differ in their lifespan and function based on various factors that determine their longevity and role in immunity.

Short-lived vs. long-lived plasma cells

Short-lived plasma cells, also called plasmablasts, typically have a lifespan of 3–5 days and are primarily involved in producing low-affinity antibodies in the early stages of an immune response. Long-lived plasma cells, on the other hand, can survive for months to a lifetime, residing mainly in the bone marrow and continuously secreting high-affinity antibodies. These long-lived cells contribute significantly to long-term immunity and are maintained in specialized survival niches that provide essential factors for their longevity.

Factors influencing plasma cell lifespan

The lifespan of plasma cells is influenced by their ability to access specialized survival niches, primarily in the bone marrow, which provides life-sustaining signals. Factors like the plasma cells' intrinsic properties, competition for niche access, and the niche's quality and composition contribute to their longevity. Additionally, turnover occurs as newly generated plasma cells displace existing ones from these niches, and variations in the antigenic stimulus and immune response can further determine plasma cell persistence.

Plasma cells in disease and immunity

Plasma cells are responsible for producing antibodies that protect the body from infections, but when they become abnormal or dysfunctional, they can lead to various immune-related disorders and cancers.

Role of plasma cells in infections and autoimmunity

When plasma cells become dysfunctional, the immune system is compromised, leading to increased susceptibility to infections. This weakened immune response makes it harder for the body to effectively fight off pathogens.
Plasma cells play a significant role in autoimmunity by continuously producing antibodies, including autoantibodies, that can target the body's own tissues. In systemic autoimmune rheumatic diseases (ARDs) such as systemic lupus erythematosus (SLE) and Sjögren's disease (SjD), plasma cells are involved in the generation of autoantibodies that contribute to chronic inflammation and tissue damage. Targeting these autoreactive plasma cells offers a promising treatment approach, although challenges remain due to their long-term survival and the need to balance depleting harmful cells while preserving protective antibody-producing cells.

Plasma cell disorders

• Multiple myeloma is a type of cancer where abnormal plasma cells accumulate in the bone marrow, disrupting the production of normal blood cells and weakening the bones.
• Waldenström macroglobulinemia is a rare blood cancer in which abnormal plasma cells and lymphocytes overproduce IgM protein, leading to symptoms such as fatigue, anemia, and complications from thickened blood.
• AL amyloidosis, or amyloid light chain amyloidosis, occurs when abnormal plasma cells in the bone marrow produce excessive light chain proteins, which misfold and accumulate in organs and tissues, leading to significant and potentially life-threatening damage.
• Diseases involving the IgG and IgA heavy chains include neoplastic plasma cell disorders where abnormal plasma cells overproduce incomplete IgG or IgA heavy chains, respectively. Patients with an IgG heavy chain disease often present with lymphadenopathy, hepatosplenomegaly, and recurring infections, whereas an IgA heavy chain disease typically affects the intestines and can cause malabsorption and abdominal lymphoma.

For more targeted research, the anti-MYEOV antibody (ab121387) from Abcam offers insight into the myeloma overexpressed gene (MYEOV), known as an oncogene in multiple myeloma. This rabbit polyclonal antibody is ideal for IHC-P and ICC/IF applications and can be critical for understanding protein overexpression in cases of myeloma.

Memory B cells vs. plasma B cells

Memory B cells and plasma B cells are both crucial components of long-term humoral immunity, but they serve distinct functions. Memory B cells do not secrete antibodies but persist in a resting state, ready to respond rapidly upon re-exposure to a specific antigen. In contrast, plasma B cells are terminally differentiated cells that continuously produce and secrete large amounts of antibodies, providing immediate defense against pathogens.
The mucosal immune system, active in areas like the gastrointestinal and respiratory tracts, is crucial for defending barrier surfaces from pathogens. Plasma B cells play a significant role in this system by secreting IgA antibodies, which help protect mucosal surfaces. Unique mucosal immune system markers, such as IgA and CCR9, are often expressed by memory B cells as well, supporting specialized immune defense in regions directly exposed to external pathogens.
Disruptions in the mucosal immune system, such as those seen in inflammatory conditions like inflammatory bowel disease (IBD), highlight the essential roles of plasma and memory B cells in maintaining effective barrier defenses and modulating inflammatory responses.

Exploring the mechanisms of chemokine receptors in plasma cell localization

Chemokine receptors play a crucial role in the localization and migration of plasma cells within the immune system. These receptors, particularly CXCR4, guide long-lived plasma cells to specific niches in the bone marrow and spleen, ensuring sustained antibody production and immune surveillance.
Chemokines and their interactions with receptors also influence the trafficking of plasma cells to tissues such as the intestines and mammary glands, regulated by receptors like CCR9 and CCR10. This precise migration is essential for maintaining long-term immunity and effective immune responses to pathogens.
For research purposes, the Anti-CXCR4 antibody [UMB2] is a recombinant monoclonal antibody specifically targeting the non-phosphorylated C-terminus of CXCR4, making it an invaluable tool for studying CXCR4's role in plasma cell migration and tissue localization. This antibody is highly suitable for various applications such as IHC-P, western blotting, and Flow Cytometry.

Cytokine production by plasma B cells

Plasma B cells are also significant producers of cytokines, contributing to immune regulation and inflammation. They can secrete both anti-inflammatory cytokines, like IL-10 and IL-35, and pro-inflammatory cytokines, such as TNF-α and IL-17, depending on the context of the immune response. This diverse cytokine production allows plasma cells to play a critical role in balancing immune responses, particularly in autoimmune diseases and infections. These highlight the functional versatility of plasma cells beyond antibody production.
At Abcam, we offer the Anti-IL-10 antibody (ab34843), which recognizes both recombinant and native human IL-10 and is crucial for detecting this cytokine in various assays, highlighting its relevance in studying the immunosuppressive functions of plasma cells.

Plasma cell applications

Plasma cells play a critical role in the immune microenvironment and have been identified as significant factors in predicting the response to immunotherapy, for example, in prostate cancer. Their subtypes can influence immune escape potential, affecting the efficacy of immunotherapy, with certain plasma cell subtypes linked to poor outcomes and lower responsiveness to treatment.
Plasma cells play a crucial role in vaccine development by producing antibodies that provide immediate and long-term protection against infections. In the context of COVID-19, vaccines stimulate naïve B cells to differentiate into plasmablasts and long-lived plasma cells, which secrete antibodies targeting the virus’s spike protein. These plasma cells reside in the bone marrow and continuously produce antibodies, contributing to sustained immunity. The strength and speed of antibody production improve with booster doses, enhancing both the neutralizing capacity and breadth of the immune response.
Just as vaccines stimulate B cells to produce antibodies against specific antigens, methods like hybridoma and recombinant monoclonal antibody production harness this ability to create targeted therapies and research tools. These techniques yield antibodies with high specificity and consistency, essential in both medical and scientific applications.

FAQs

What are the main functions of plasma B cells?

Plasma B cells primarily function to secrete large quantities of antibodies that are crucial for targeting and neutralizing specific pathogens, playing a key role in humoral immunity and long-term protection.

How long do plasma B cells live?

Plasma B cells can live for a few days if they are short-lived or for several months to a lifetime if they are long-lived, depending on their environment and support from survival niches like those in bone marrow.

How do plasma cells contribute to neuro-inflammation?

Plasma cells contribute to neuroinflammation by producing antibodies that target central nervous system (CNS) components, leading to immune-mediated damage. They also secrete inflammatory cytokines that can further exacerbate neuroinflammatory conditions such as multiple sclerosis and autoimmune encephalitis.