Immune cells called lymphocytes reside temporarily in lymphoid tissue. There, they develop and mature before moving to other parts of the body to fight infection.
There are two main types of lymphocytes: B cells and T cells. B cells produce antibodies, protein molecules that bind to foreign invaders like bacteria or viruses.
T cells regulate immune responses by either activating or suppressing other immune cells. Additionally, some T cells can actually kill infected target cellssuch as cancer cellsthereby playing a role in immunotherapy treatments.
Immunotherapy treatments use lymphocyte therapies to fight disease. These therapies can be administered through direct injection into the patient’s body, or through infusion into the bloodstream. They can target either B cells or T cells, depending on the type of disease.
This article will discuss the development and maturation of lymphocytes, as well as the types of immunotherapy that target different types of lymphocytes.
What is lymphoid tissue?
Along with lymphocytes, lymphoid tissue consists of cells called plasma cells and B cells, macrophages and dendritic cells.
Plasma cells produce antibodies that fight off infection. B cells produce antibody molecules that attach to foreign invaders, marking them for attack by other immune system components and facilitating their elimination.
Macrophages and dendritic cells function as sentinels or patrol cells, scanning the surrounding tissues for signs of infection or damage.
They also participate in immune responses by presenting fragments of invaders to T Cells and producing chemicals that promote activation of more immune system components.
All of these cell types reside temporarily in lymphoid tissue. When there is no longer a need for them in that location, they move to other parts of the body to respond to new threats.
How do lymphocytes move?
Along with dendritic cells and monocytes, lymphocytes reside temporarily in lymphoid tissue.
Once a lymphocyte has undergone the process of differentiation, it is said to be an effector cell. Effector cells have functions that protect the body from harmful invaders, such as bacteria or viruses.
Lymphocytes circulate through the body via blood vessels. They do not stay in one place, but rather travel throughout the body to wherever they are needed. This process is called circulatory migration.
Circulatory migration begins in the thymus, where T-cells mature. Once a T-cell has been exposed to a threat, it moves to the bone marrow where it can continue to proliferate and differentiate into other types of T-cells. From there it travels to the peripheral blood where it can respond to external stimuli.
What are B cells?
B cells, also called B lymphocytes or immune cells, are part of the lymphocyte family. B cells reside temporarily in lymphoid tissue, then move to other parts of the body to fight infections.
B cells originate in the bone marrow where they undergo specialization to carry out their role in immune responses. Specifically, B cells undergo cell differentiation into plasma cells which produce antibodies.
Antibodies are protein molecules that can recognize and bind to pathogens like bacteria or viruses. This recognition and binding triggers a response against the pathogen, either killing it or pulling it into other parts of the body for elimination.
B cell differentiation also occurs in response to cytokines, small proteins that facilitate communication between immune and other systems in the body. Interferon is one type of cytokine that promotes activation of B cells.
What are T cells?
T cells are a type of lymphocyte. Lymphocytes are a class of white blood cell. There are several different types of lymphocytes, and they all play different roles in our immune system.
T cells come in many different subtypes, which is why they are also called T-cell receptors. All T cells have a protein on their surface called CD8.
This CD8 protein is what allows T cells to recognize infected or damaged cells and attack them. This process is called cell-mediated immunity and it is what helps fight off infections like the flu or Herpes simplex virus 1 (HSV-1).
Other lymphocytes include B cells, natural killer (NK) cells, and innate lymphoid cell (iLC)s. All of these play important roles in our immune system as well.
What is the structure of a normal lymphocyte?
A normal lymphocyte consists of a cell body, also called a cyton, a nucleus, and usually several external structures called antigens. Cell bodies are usually round in shape and contain the vital components needed to sustain life.
Cell bodies contain enzymes needed to breakdown molecules outside the cell and re-use them to maintain the cyton. The nucleus contains the DNA needed to make the cell what it is. Antigens are proteins or peptides on the cell that can be recognized by other cells or agents as foreign.
Lymphocytes undergo changes that can make them more effective at fighting infection. One of these changes is called differentiation. During differentiation, lymphocytes change shape and acquire new functions including internal structures such as cytons.
What do they do?
Once lymphocytes are produced in the thymus and blood, they move into lymphoid tissue. There, they monitor for infection and immune system dysfunction.
There are several types of lymphocytes, each with a specific function. T cells function in cell-mediated immunity, whereas B cells function in antibody immunity. Regulatory T cells suppress other immune cells, whereas cytotoxic T cells kill infected or abnormal cells.
Natural killer (NK) cells function in both cell-mediated and antibody immunities. Antibody immune functions include protection against viruses or disease by identifying and targeting them.
Macrophages also function in antibody immunity by clearing out dead or dysfunctional tissues or infectious agents. These types of lymphocytes all reside temporarily in lymphoid tissue to perform their functions.
Where are they stored?
Once lymphocytes have been programmed in the thymus or in secondary lymphoid tissues like the lymph nodes or spleen, they are then sent to different parts of the body to start its important job.
They are sent to either blood vessels or other tissues where pathogens can enter and cause an immune response.
They can also be stored in a special area of the lymph node called the follicle, where they can be recalled when needed.
Interestingly, when lymphocytes are needed somewhere else, they do not return to the thymus to mature further. Rather, new cells that have not yet traveled to other parts of the body take their place in the thymus. This process is called turnover and ensures that there are always new and ready immune cells.
Do all humans have the same number of lymphocytes?
No, humans do not have the same number of lymphocytes. The number can vary from person to person depending on how many cells are being produced and how many are destroyed.
Some people have fewer lymphocytes, while others have more. People with higher numbers of lymphocytes may be more immune system competent than those with lower numbers.
The average human has about one billion lymphocytes per microliter of blood. A microliter is one one-hundredth (0.001) of a liter, which is the standard unit of volume for blood. One billion is a very large number!
The average human produces about one billion new lymphocytes every day. This process is called proliferation. New cells are produced in an area called the bone marrow. These new cells then move into the blood and other tissues where they work to fight infection.
