What is the Difference Between B Cells and Plasma Cells

The main difference between B cells and plasma cells is that the B cells are a type of white blood cells involved in adaptive immunity whereas the plasma cells are activated B cells. 

B cells and plasma cells are two types of white blood cells in adaptive immunity. Here, the B cells are responsible for the production of antibodies, serve as antigen-presenting cells, and secrete antibodies while the main function of plasma cells is to produce a large number of antibodies.

Key Areas Covered

1. What are B Cells
     – Definition, Types, Features
2. What are Plasma Cells
     – Definition, B Cell Activation, Function
3. What are the Similarities Between B Cells and Plasma Cells
     – Outline of Common Features
4. What is the Difference Between B Cells and Plasma Cells
     – Comparison of Key Differences

Key Terms

B Cells, B Cell Activation, Memory Cells, Plasma Cells, Plasmablasts

What are B Cells

B cells are a type of white blood cells in the circulation. They are one of the two types of lymphocytes; B lymphocytes. T lymphocyte is the second type of lymphocytes. The main function of B cells is to produce antibodies against pathogens. Hence, these cells are a component of the adaptive immunity. However, the function of the B cells depends on the type of B cell. There are several types of B cell as follows: 

1. Naïve B cells – B cells that are not exposed to an antigen. Once exposed, naïve B cells can differentiate into other types of B cells.
2. Plasmablast – Early stage of B cell differentiation in response to exposure to an antigen. It is a short-lived cell, which can proliferate. It produces a small number of antibodies when compared to plasma cells.
3. Plasma cell – Final stage of B cell proliferation. It is a long-lived B cell that is unable to proliferate. It secretes the highest amount of antibodies.
4. Memory B cell – Dormant stage of B cell differentiation. It has the longest lifespan among the B cell types. It circulates throughout the body in order to generate a stronger immune response known as the secondary antibody response.
   

   Figure 1: B Cell Differentiation

5. B-2 cell (FO B cells and MZ B cells) – FO B cells are the most common type of B cells responsible for the production of high-affinity antibodies. They occur in the secondary lymphoid organs or lymphoid follicles when not circulating. On the other hand, the MZ B cells are responsible for the first line defence against blood-borne pathogens. They occur in the marginal zone of the spleen.
6. B-1 cells – Produce natural antibodies against the mucosal pathogens. They occur in the peritoneal and the pleural cavity.

What are Plasma Cells

Plasma cells are a type of B cells responsible for the production of antibodies against a specific pathogen. They are a type of differentiated B cells upon the exposure to a particular antigen in a process called B cell activation.

Figure 2: B Cell Activation

Looking at its production; the production of B cells occurs in the bone marrow. First, B cells leave the bone marrow to serve as the antigen presenting cells (APCs). Then they internalize antigens via receptor-mediated endocytosis. Next, they present the processed antigens along with the MHC class II molecules to the T helper cells. The binding of the T helper cells to MHC class II molecules causes the activation of the B cell. Upon activation, the germinal centre of the B cell can either differentiate into a plasma B cell or a memory B cell. Moreover, the activated B cells first differentiate into plasmablasts and then, they become plasma cells. Here, the plasmablasts produce a small number of antibodies but, the plasma cells are responsible for the production of a large number of specific antibodies.

Similarities Between B Cells and Plasma Cells

• B cells and plasma cells are two types of white blood cells in the circulation.
• Both are lymphocytes; hence, they do not contain granules in the cytoplasm.
• Also, both of their nucleus is large and round in shape.
• Besides, both have an important role in adaptive immunity by producing antibodies.

Difference Between B Cells and Plasma Cells

Definition

B cells refer to the lymphocytes that are not processed by the thymus gland, and responsible for producing antibodies while plasma cells refer a fully differentiated B-lymphocyte, which produces a single type of antibody. Thus, this is the main difference between B cells and plasma cells.

Significance

Moreover, there are several types of B cells as naïve B cells, plasmablast, memory B cells, and plasma cells while plasma cells is a type of activated B cells.

Function

A major difference between B cells and plasma cells is their function. B cells serve as antigen presenting cells, produce cytokines, and secrete antibodies while the main function of plasma cells is to secrete antibodies.

Proliferation

Other types of B cells can proliferate while plasma cells do not proliferate. Hence, this is another difference between B cells and Plasma cells.

Conclusion

B cells are a type of lymphocytes responsible for the production of antibodies in adaptive immunity. Here, the B cells that are not exposed to an antigen are called naïve B cells. Upon exposure, it differentiates either into a plasma cell or memory cell. Plasma cells are the main type of B cells, which produce a large number of specific antibodies. Therefore, in conclusion, the main difference between B cells and plasma cells is the degree of differentiation and the production of antibodies.

Reference:

1. “6. B Cell Activation and Plasma Cell Differentiation.” Immunopaedia.org, Available Here

Image Courtesy:

1. “B cell activation naive to plasma cell” By Bobologist – adobe illustrator (CC BY-SA 3.0) via Commons Wikimedia
2. “B cell function” By Arizona Science Center –  (CC BY-SA 3.0) via Commons Wikimedia