Things To Know About Lymphocytes

What are lymphocytes?

Lymphocytes are one of the three types of white blood cells. They are a part of the body’s adaptive immunity and play a crucial role in fighting against infection and disease-causing microbes. 

Lymphocytes are high in number in blood and lymph (the colorless fluid that connects lymph nodes to blood circulation). The lymphatic system is a network of small and large vessels, organs, and tissues that protect the body.

Lymphocytes develop in primary lymphoid organs (the thymus gland and hematopoietic or blood-forming tissue in the bone marrow) and most of them die without functioning at all. The rest of the cells are constantly circulating between the lymph and blood. When they encounter or recognize a foreign antigen in a peripheral lymphoid organ (lymph nodes, spleen), lymphocytes proliferate into different types of cells to attack the foreign cells. 

An antigen is a marker, usually, a protein found on the surface of cells. If they are foreign to the body, they are tagged and identified by lymphocytes. Lymphocytes then migrate through the blood to the site of infection. Lymphocytes are the highest in number in lymph nodes. These nodes are small organs that filter lymph and isolate microbes that can be later attacked by lymphocytes. Lymphocytes differentiate into different types only when they are activated by a foreign cell. 

Functions of lymphocytes 

The main function of lymphocytes is to fight foreign cells like viruses, bacteria, and cancer by identifying the antigens on these cells. They are an important component of the body's immune system to fight infection.

An important property of lymphocytes that helps them perform this function is their memory. Every time they encounter an antigen they store it in memory. The next time they encounter the same antigen, they can recognize it and respond quickly. This is the basis of how vaccinations work to prevent certain infections.

Types of lymphocytes 

Lymphocytes are of 2 main types, with each having its subtypes

B cells or B lymphocytes are responsible for humoral or antibody-mediated immunity. An antibody is a protein that binds to a specific antigen. There are 2 categories of B lymphocytes:

1. Plasma cells produce antibodies in response to an infection. The antibodies or immunoglobulins bind to the antigens to neutralize them or prepare them for destruction by other cells. 
2. Memory B cells help to remember and recognize foreign cells and attack them if the infection returns.

T cells or T lymphocytes are involved in cell-mediated immunity in which there is the activation of cells and release of chemicals like cytokines in response to an antigen. The different types of T lymphocytes are:

1. Cytotoxic cells upon being activated kill infected cells. 
2. Helper cells are involved in gathering other cells to fight the infection.
3. Natural killer cells are capable of killing certain cancer cells and other infection-causing cells. They are part of the frontline immune response.
4. Regulatory T cells help to regulate the entire reaction and prevent any harm to the body that can be caused by overreaction (as in autoimmune conditions).
5. Memory T cells are responsible for remembering antigens to launch attacks if reinfection happens.

Where are lymphocytes found?

B and T lymphocytes develop from stem cells present in the bone marrow. Some immature cells migrate from the bone marrow to the thymus gland where they become T cells. B cells develop within the bone marrow. 

Both B and T cells migrate to peripheral lymphoid organs like the spleen and liver from where they react with antigens.

How do lymphocytes look?

Lymphocytes are microscopic, larger than red blood cells but fewer in number. They consist almost entirely of a large central nucleus surrounded by a jelly-like cytoplasm. When observed after staining, the nucleus is dark purple and the cytoplasm becomes lighter pink.

Normal range of lymphocytes

Usually, lymphocytes constitute about 20–40% of the total white blood cells in the blood. The normal lymphocyte count depends on various factors like age, sex, altitude, and lifestyle.

In adults, the count ranges from 1000 to 4800 per microlitre, and in children, it ranges from 3000 to 9500 lymphocytes per microlitre of blood. 

What does a high lymphocyte count mean?

When the count of lymphocytes is high (>4000/microlitre for adults), it is called lymphocytosis. It usually means the body is producing more lymphocytes to fight an infection or illness such as:

• Recent viral infection
• Chronic medical conditions like rheumatoid arthritis
• An allergic reaction to a medicinal drug
• Trauma
• Splenectomy (surgical removal of the spleen), or absence of the spleen.

Lymphocytosis can also indicate certain serious conditions, such as: 

• Hepatitis
• Syphilis, primary HIV or AIDS
• Whooping cough, Tuberculosis
• Toxoplasmosis, cytomegalovirus
• Blood cancers like leukemia and lymphoma. Often, high lymphocytes are the first sign of these kinds of cancer. 

High lymphocyte count cannot be usually prevented, but it can be managed by treating the underlying cause.

How does a low lymphocyte count affect health?

Lymphocytopenia or lymphopenia is the opposite of high lymphocyte count and refers to a condition in which the lymphocyte count in blood is lower than normal. This usually means the count is <1000/microlitre in adults or <3000/microlitre in children below 2 years. Poor nutrition is one of the main risk factors for lymphopenia. The condition makes a person prone to infection. It could be caused by mild infections like the flu or due to more serious conditions like:

• HIV or AIDS
• Tuberculosis, typhoid
• Viral hepatitis
• Hodgkin’s lymphoma
• Autoimmune conditions like systemic lupus erythematosus
• Radiation therapy, chemotherapy for cancer
• Rare inherited conditions such as SCID (Severe Combined ImmunoDeficiency) syndrome.

Common tests to check the health of lymphocytes

The following are some of the tests to check lymphocyte count in a blood sample:

1. Absolute lymphocytes count: As part of a complete blood count (CBC ) - A CBC gives the percentage of each type of white blood cell. Multiplying the total white blood cell count by the percentage of lymphocytes gives the absolute lymphocyte count.
2. Flow cytometry: This is an advanced test in which blood is processed in a special laboratory. The blood sample is suspended in a fluid and passed through a laser-generating instrument. The laser light scatters blood cells into patterns that make it possible to count and analyze individual blood cells.

Symptoms of lymphocyte count

Lymphocytosis symptoms

A blood disorder or any cancer may lead to a high lymphocyte count with a few symptoms like:

• Enlarged lymph nodes – Swollen lymph nodes indicate that the body is reacting or fighting an infection. It could be a respiratory infection or any other viral or bacterial infection. The nodes are soft, tender, and slightly movable. An enlarged node is a filter to get rid of pathogens that pass through lymph, a fluid made up of white blood cells and proteins.
• Fever, night sweats
• Pain in the abdomen
• Loss of appetite
• Shortness of breath – It is an indication of a heart or lung illness, asthma, or allergy.

Lymphopenia symptoms

Lymphopenia may not cause any symptoms, but when it is found during testing for any other condition the following signs and symptoms may be present:

• Recurrent infections like the common cold
• Presence of fungal or parasitic infections that rarely occur in people with a healthy immune system
• Chronic infections like tuberculosis
• Enlarged or swollen lymph nodes
• Smaller or missing tonsils
• Sudden hair loss, chronic itch, red skin
• Small swellings on the skin that turn into open sores
• Jaundice or yellowing of skin and eyes
• Ulcers in the mouth
• Enlarged spleen.