Our immune system is the defensive system in a host, which consists of differently distributed tissues and organs. Lymphocytes are the essential cells of the immune system and are responsible for the adaptive immunity in an organism. The two lymphocytes are – B and T lymphocytes. And they originate from the lymphoid progenitors. They are responsible for many of the characteristics involved in immune response like- diversity, specificity, memory for the infection, and self or nonself- recognition. There are many similarities between B cells and T cells, and also they share some differences.

The immune system is complex. And the cells involved in our immune system are called the immune cells and include lymphocytes. These cells work in coordination with other cells to fight foreign infections. The cells which are responsible for both nonspecific and specific immunity are the leukocytes or white blood cells. 

The leukocytes are formed from the multipotent hematopoietic stem cell type of cell. During hematopoiesis, these hematopoietic stem cells differentiate with two pathways giving rise to lymphoid progenitor cells or myeloid progenitors. The lymphoid progenitor gives rise to B cells, T cells and natural killer cells.

• The B cells help produce antibodies that can bind to the antigen and destroy the capturing infection.
• While the T cells are the direct fighters of the infection and produce cytokines involved in the activation of other parts of the immune system.

B lymphocytes

The B lymphocytes mature in the bone marrow in most mammalian species and express the membrane-bound antibody. B cells play an important role in pathogen-specific immunity by giving rise to antibodies. They recognise the antigen, which is soluble by the antibodies (immunoglobulins) attached to their surface and give rise to antibody-producing cells called plasma cells and memory cells. They are the only cells that can produce antibodies, so they are the central cellular component of the humoral immune response. B cells also serve as antigen-presenting cells (APCs). APCs are the cells involved in presenting antigens to naive T cells.

• The origin and maturation of B lymphocytes occur in the bone marrow. (Bursa of Fabricius in bird)
• Expression of the antigen receptor in the bone marrow.
• Differentiation occurs in the lymphoid tissue.
• The surface immunoglobulin or antibodies are present.
• Humoral immunity 
• The distribution of B cells is in the spleen, lymph nodes, bone marrow, and other lymphoid tissue.
• Secretory products are antibodies and cytokines.
• Complement receptors are present.

T lymphocyte

They originate in the bone marrow, but maturation occurs in the thymus. From bone marrow, they travel to the thymus gland for development. They express a very different and unique antigen-binding molecule known as the T cell receptor during the maturation process. They do not produce antibodies but perform effector functions during antigen presentation. The T lymphocyte is part of adaptive immunity and the primary effector for cell-mediated immunity. There are two types of a subpopulation of T cells- one is the T helper cell, and the other is the cytotoxic T cell.

• They originate in the bone marrow.
• The maturation takes place in the thymus gland.
• Expression of the Ag receptor is in the thymus.
• Differentiation occurs in lymphoid tissue.
• The surface immunoglobulins are absent in T cells.
• The immunity provided by T cells is cell-mediated as well as humoral.
• Secretory products are cytokines.
• Receptors are the TCRs that are present on the membrane.

Similarities between B lymphocyte and T lymphocyte

• Both of these cells originate from the lymphoid progenitor cells.
• Both are lymphocytes. (lymphocytes are the mononuclear leukocytes with 20% to 40% of total white blood cells.
• The production of both these cells occurs in the bone marrow. 
• Both are nonphagocytic cells which means they do not protect the body from foreign particles like bacteria, dead cells, etc., by ingesting them as they both have different mechanisms to destroy the infection. 
• Both of them are nucleated cells and have a large nucleus. 
• They are motile and are found in peripheral blood and all lymphoid tissues.
• Both of them have a role to play in the adaptive immune response of organisms.
• These cells can not be differentiated under a light microscope as they both are morphologically similar. 
• Both have cell surface receptors for binding the antigen. B cell receptor and T cell receptor).
• These cells arise from the liver and yolk sac stem cells during the embryo’s development.

Conclusion

B and T cells have different functions, but they also share some similarities. They are morphologically similar and appear similar in; a light microscope. Both types of cells originate from bone marrow, are motile, have large nuclei, and are non-phagocytic cells. Even though they have a lot of differences, both belong to types of lymphocytes and are part of the lymphoid progenitor.