What are Monocytes?
Monocytes are one of the largest types of WBC, which helps to regulate the immune system and fight against foreign particles or any kind of infection in our body. It is an immune cell manufactured in bone marrow travelled through the blood to the tissues in the whole body, where it changed to a dendritic cell or macrophage. Macrophages kill microorganisms, remove dead cells, ingest foreign materials and boost the immune system. Monocyte is a type of phagocyte and a type of white blood cells.
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Any kind of infection in the body, like bacterial, viral or fungal, causes an increase in monocyte levels. It happens because the body starts fighting the infection and creates monocytes to fight the foreign body. A monocyte high is also caused by autoimmune disorders, chronic infections and sometimes by stress too.
Anything that causes suppression of the immune system causes low monocyte counts. There are various causes of suppression of the immune system such as chemotherapy and radiation therapy, cancer, HIV, and AIDS that weakens the body immune system and bloodstream infection, sepsis.
Structure of Monocyte
The monocytes are the largest cells that are present in the peripheral blood. They have a diameter that is between the range of 14 to 20 micrometres. The appearance of the cell is somewhat irregular in shape, and it has a kidney-shaped or an oval-shaped nucleus present along with some cytoplasmic material. The nucleus to cytoplasm ratio of monocytes is quite high, which is 3:1. The nucleus of the monocyte is quite prominent and is folded. There are a large number of granules present in the cytoplasm. These granules of monocytes are known as cytoplasmic granules. The number of these granules is more towards the cell membrane. There is a chromatin net present in the nucleus. There are also chromatin clumps that are seen in the nuclear membrane towards its inner side. On the surface of the monocyte, there are some blebs and ruffles that have some functional significance.
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Since Monocytes are phagocytic and motile in nature, the irregular formation and ruffles present on the surface make the repulsive forces a bit less, with the negatively charged groups approaching the cell. There are numerous mitochondria present in the cytoplasm that are small in size and somewhat elongated. We can also see a golgi complex present along with a centrosome inside the nucleus. In addition, there are many microvilli present on the cell membrane that helps in the movement and adherence of monocytes to the other cells. The cytoplasmic granules have a very smaller diameter which is of about 0.05 to 0.2 micrometres. However, they are homogeneous and dense.
Presence of Monocytes
A certain amount of monocytes migrate in and out of the required organ tissues.
In the spleen, quite good numbers of monocytes migrate to the tissue from the body and reside there to give rise to numbers of macrophages which essentially fight infection and clear dead cells.
How to Increase monocytes- Low monocytes treatment
There are several ways to increase monocytes levels in our body, such as regular exercise, maintaining a healthy weight, minimizing stress levels, smoking cessation, and last but not least good sleep.
Conditions associated with Monocyte low counts (Monocytopenia)
There are various conditions associated with Monocytopenia (deficiency of monocytes). Cancer chemotherapy helps to improve the quality of life of a human being, also causes various conditions such as Monocytopenia due to the use of chemotherapeutic agents. Other reasons for Monocytopenia are:
Leukaemia
Vitamin B12 deficiency
Rheumatoid arthritis
Corticosteroid therapy
HIV infection
Radiation therapy
Sometimes severe burns too
Monocyte High Counts (Monocytosis)
Monocytosis, state of the increased number of monocytes in the blood, which may indicate various diseases such as,
Necrosis
Red blood cell regeneration
Atherosclerosis
Sarcoidosis
Immune-mediated diseases.
Role of the Immune system in Monocytopenia and Monocytosis
The immune system plays a vital role in our survival. Still, in the case of monocytopenia and monocytosis, both conditions are harmful to the body means hyperactivity of the immune system leads to various severe diseases and sometimes may cause death too.
FAQs on Monocytes
1. What are monocytes and what is their primary function in the immune system?
Monocytes are the largest type of white blood cell (leukocyte) and are classified as agranulocytes. Their primary function is to serve as a crucial part of the body's innate immune defence. They circulate in the bloodstream before migrating into tissues, where they differentiate into macrophages or dendritic cells. Their key roles include phagocytosis (engulfing and digesting pathogens, dead cells, and debris), releasing chemical signals (cytokines) to orchestrate an immune response, and presenting antigens to lymphocytes to activate the adaptive immune system.
2. What is considered a normal monocyte count in a blood test?
A normal monocyte count typically falls within a specific range, which is measured as part of a Complete Blood Count (CBC) with a differential test. In a healthy adult, monocytes usually make up 2% to 8% of the total white blood cell count. In absolute numbers, this generally corresponds to a range of 200 to 800 monocytes per microliter of blood. Values may vary slightly depending on the laboratory.
3. How do monocytes differ from macrophages?
Monocytes and macrophages are closely related but represent different stages of the same cell lineage. The key differences are:
- Location: Monocytes are found circulating in the bloodstream, whereas macrophages are found resident in body tissues (like the lungs, liver, and spleen).
- Maturity and Size: Monocytes are considered immature precursors. Macrophages are larger, more complex cells that have differentiated from monocytes after leaving the blood.
- Function: While monocytes are capable of phagocytosis, macrophages are professional phagocytes with a much greater capacity for engulfing pathogens. Macrophages are also more involved in long-term tissue repair and signalling.
Essentially, a monocyte is a macrophage-in-training that travels through the blood.
4. Where are monocytes produced and how do they mature?
Monocytes are produced in the bone marrow from hematopoietic stem cells through a process called monocytopoiesis. After their formation, they are released into the bloodstream and circulate for about 1 to 3 days. Their maturation is completed when they receive chemical signals from sites of infection or inflammation, causing them to leave the circulation and migrate into body tissues. Once in the tissue, they undergo a final differentiation to become either a macrophage or a dendritic cell, fully equipping them for their specialised immune functions.
5. What does a high monocyte count (monocytosis) typically indicate?
A high monocyte count, a condition known as monocytosis, is usually a sign that the body is fighting off a certain type of infection or dealing with an inflammatory condition. It is not a disease itself but an indicator of an underlying issue. Common causes include chronic infections (like tuberculosis), autoimmune diseases (like lupus or rheumatoid arthritis), certain blood disorders, and some types of cancer. The elevated count reflects an increased demand for monocytes to differentiate into macrophages to combat persistent pathogens or inflammation.
6. What are the implications of having a low monocyte count (monocytopenia)?
A low monocyte count, or monocytopenia, can make a person more susceptible to infections, particularly from certain bacteria, fungi, and protozoa. This condition often results from issues that affect the bone marrow, where monocytes are produced. Potential causes include chemotherapy, radiation therapy, sepsis (overwhelming bloodstream infection), or bone marrow disorders like aplastic anemia. A consistently low count is a concern because it weakens a key component of the body's first line of defence.
7. Why are monocytes considered a critical link between the innate and adaptive immune systems?
Monocytes are a critical bridge between the general (innate) and specific (adaptive) immune systems because of their role as Antigen-Presenting Cells (APCs). After a monocyte or its descendant, the macrophage, engulfs a pathogen, it breaks it down and displays a piece of it (the antigen) on its cell surface. It then travels to a lymph node and presents this antigen to T-lymphocytes. This act of presentation is the key signal that activates the T-cells, launching the highly specific and powerful adaptive immune response. Without this link, the body's targeted response would be much slower and less effective.
