Antibodies are Y-shaped proteins produced as part of the body’s immune response to infection. They help eliminate disease-causing microbes from the body, for instance by directly destroying them or by blocking them from infecting cells.
Antibodies work by recognising and sticking to specific proteins, such as those found on the surfaces of viruses and bacteria, in a highly specific way. When the body encounters a microbe for the first time, immune cells produce antibodies that specifically recognise proteins associated with that particular microbe.
After recovering from an infection or receiving a vaccine, a small number of these antibody-producing immune cells usually remain in the body as memory cells, providing immunity to future infections with the same bug. Because memory cells and antibodies are already present, next time the body encounters the same microbe, the immune response is much faster and can stop the infection from taking hold.
Antibody testing
Antibody tests – also known as serological tests – take advantage of the microbe-specific antibodies that remain in the blood after a person has recovered from an infection. Blood samples can be tested for the presence of microbe-specific antibodies by mixing them with proteins from the relevant microbe, called antigens. If there are specific antibodies present in the blood sample, they will stick to the antigens.
Because it takes a while for the body to generate antibodies against a new microbe, it is only possible to detect antibodies in the blood from about two weeks after infection onward. This means antibody tests cannot detect infections at an early stage. Instead, antibody tests can provide a useful way of determining whether or not someone has had a particular infection. Commonly used examples are HIV and hepatitis B tests.
Therapeutic antibodies
The ability of antibodies to specifically bind to certain proteins means they can also be used as therapies in some cases. For example, antibody therapies, such as checkpoint inhibitors, are already used to treat a number of cancers. Checkpoint inhibitors are antibodies that stick to and block the actions of proteins called checkpoints, which would otherwise suppress the body’s immune responses to the cancer cells.
In some cases, antibodies from humans or animals that are immune to an infection can be given to people as a treatment, although producing antibodies in sufficient quantities can be challenging. Rabies can be treated by giving people human rabies antibodies, called human rabies immunoglobulin.
Giving people antibodies provides passive immunity because the person receiving the antibodies is not immune, but is temporarily protected by the antibodies they receive. Passive immunity occurs naturally during pregnancy, when maternal antibodies are transferred to the foetus through the placenta. Maternal antibodies are also transferred to babies through breastfeeding.
Antibodies that cause harm
Antibodies that recognise the body’s own proteins, instead of proteins from infectious microbes, can cause harm. In autoimmune diseases, such as lupus, multiple sclerosis and rheumatoid arthritis, people produce antibodies that stick to their body’s own proteins and attack healthy cells.
Allergies involve a special class of antibodies called immunoglobulin E (IgE). When these antibodies detect allergens, they trigger immune cells to release histamine and other inflammatory molecules, which can cause the nasty symptoms associated with allergic reactions.
Other uses of antibodies
Because of their unique ability to recognise and stick to specific proteins, antibodies are commonly used as a tool in biomedical research, for example to identify whether a particular protein is present in a sample or to find out where a specific protein is located within a cell.
- Types and function
- Normal ranges
- Test
- Conditions
- How to raise or lower
- Summary
White blood cells circulate around the blood and help the immune system fight off infections.
Stem cells in the bone marrow are responsible for producing white blood cells. The bone marrow then stores an estimated 80–90% of white blood cells.
When an infection or inflammatory condition occurs, the body releases white blood cells to help fight the infection.
In this article, learn more about white blood cells, including the types and their functions.
Health professionals have identified three main categories of white blood cell: granulocytes, lymphocytes, and monocytes. The sections below discuss these in more detail.
Granulocytes
Granulocytes are white blood cells that have small granules containing proteins. There are three types of granulocyte cells:
- Basophils: These represent less than 1% of white blood cells in the body and are typically present in increased numbers after an allergic reaction.
- Eosinophils: These are responsible for responding to infections that parasites cause. They also play a role in the general immune response, as well as the inflammatory response, in the body.
- Neutrophils: These represent the majority of white blood cells in the body. They act as scavengers, helping surround and destroy bacteria and fungi that may be present in the body.
Lymphocytes
These white blood cells include the following:
- B cells: Also known as B-lymphocytes, these cells produce antibodies to help the immune system mount a response to infection.
- T cells: Also known as T-lymphocytes, these white blood cells help recognize and remove infection-causing cells.
- Natural killer cells: These cells are responsible for attacking and killing viral cells, as well as cancer cells.
Monocytes
Monocytes are white blood cells that make up around 2–8% of the total white blood cell count in the body. These are present when the body fights off chronic infections.
They target and destroy cells that cause infections.
According to an article in American Family Physician, the normal range (per cubic millimeter) of white blood cells based on age are:
| Age | Normal range |
| Newborn infant | 13,000–38,000 |
| 2-week-old infant | 5,000–20,000 |
| Adult | 4,500–11,000 |
The normal range for a pregnant women in the 3rd trimester is 5,800–13,200 per cubic millimeter.
High white blood cell count
If a person’s body is producing more white blood cells than it should be, doctors call this leukocytosis.
A high white blood cell count may indicate the following medical conditions:
- allergic responses, such as due to an asthma attack
- those that may cause cells to die, such as burns, heart attack, and trauma
- inflammatory conditions, such as rheumatoid arthritis, inflammatory bowel disease, or vasculitis
- infections, such as with bacteria, viruses, fungi, or parasites
- leukemia
Surgical procedures that cause cells to die can also cause a high white blood cell count.
Low white blood cell count
If a person’s body is producing fewer white blood cells than it should be, doctors call this leukopenia.
Conditions that can cause leukopenia include:
Doctors may continually monitor white blood cells to determine if the body is mounting an immune response to an infection.
During a physical examination, a doctor may perform a white blood cell count (WBC) using a blood test. They may order a WBC to test for, or rule out, other conditions that may affect white blood cells.
Although a blood sample is the most common approach to testing for white blood cells, a doctor can also test other body fluids, such as cerebrospinal fluid, for the presence of white blood cells.
A doctor may order a WBC to:
- test for allergies
- test for infection
- test for leukemia
- monitor the progression of certain conditions
- monitor the effectiveness of some treatments, such as bone marrow transplants
The following are conditions that may impact how many white blood cells a person has in their body.
Aplastic anemia
This is a condition wherein a person’s body destroys stem cells in the bone marrow.
Stem cells are responsible for creating new white blood cells, red blood cells, and platelets.
Evans syndrome
This is an autoimmune condition wherein the body’s immune system destroys healthy cells, including red and white blood cells.
HIV
HIV can decrease the amount of white blood cells called CD4 T cells. When a person’s T cell count drops below 200, a doctor might diagnose AIDS.
Leukemia
Leukemia is a type of cancer that affects the blood and bone marrow. Leukemia occurs when white blood cells rapidly produce and are not able to fight infections.
Primary myelofibrosis
This condition causes a person’s body to overproduce some types of blood cells. It causes scarring in a person’s bone marrow.
Whether or not a person needs to alter their white blood cell count will depend on the diagnosis.
If they have a medical condition that affects the number of white blood cells in their body, they should talk to a doctor about the goals for their white blood cell count, depending on their current treatment plan.
A person can lower their white blood cell count by taking medications such as hydroxyurea or undergoing leukapheresis, which is a procedure that uses a machine to filter the blood.
If a person’s white blood cell count is low due to cancer treatments such as chemotherapy, a doctor may recommend avoiding foods that contain bacteria. This may help prevent infections.
A person can also take colony-stimulating factors. These may help prevent infection and increase the number of white blood cells in the body.
White blood cells are an important part of the body’s immune system response. There are different types of white blood cell, and each has a specific function in the body.
Certain conditions can affect the number of white blood cells in the body, causing them to be too high or too low.
If necessary, a person can take medication to alter their white blood cell count.
Last medically reviewed on January 9, 2020
- Blood / Hematology
- Immune System / Vaccines
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