Concerned about monocytosis and its implications for your health? No worries, you’re in the right place. Understanding monocytosis and the differences between acute and chronic can be essential for diagnosing and managing various health conditions. Here, we’ll break down the differences between these two conditions. 

What are monocytes?

Monocytes are a type of white blood cell that support your immune system. They are responsible for fighting against infections caused by toxic or foreign substances.¹ An increase of monocytes in the blood to an abnormally high level is known as monocytosis. Acute and chronic monocytosis involve abnormally high levels of monocytes; the core difference between these two conditions is how long these high levels of monocytes remain in the body.

What is acute monocytosis?

• Monocytes are elevated for a short period
• Bacteria, viruses, inflammation, pregnancy, and certain medications can lead to acute monocytosis. inflammation, stress responses, pregnancy, and even certain medications
• Symptoms include fever and fatigue, depending on how intense the pain and inflammation are
• The level of monocytes returns to normal once the underlying cause has been identified and treated²

What is chronic monocytosis?

• Monocytes are elevated for a longer time, often indicating a more serious underlying health issue
• Severe conditions such as tuberculosis, fungal infections, inflammatory conditions,  mononucleosis, autoimmune diseases such as lupus and rheumatoid arthritis, leukaemia, and other hematologic disorders can lead to chronic monocytosis
• Prolonged duration is often observed to persist long-term, ranging from months to years² 

It’s important to note that monocytosis itself doesn’t usually cause symptoms, but rather any symptoms experienced are those of whichever medical condition/s lead to your extremely high monocyte levels.³ 

Better understanding monocytes and their origins, functions and functional pathways can also provide further insight into how an increase in their presence has caused for concern.

Though monocytes, alongside the 4 other types of white blood cells (basophils, eosinophils, lymphocytes and neutrophils) make up approximately 1% of your blood, they are all crucial players in your body’s internal defence system.

Produced in the bone marrow (aka Haematopoiesis), monocytes possess the ability to isolate and get rid of toxic and foreign microorganisms and dead cells and also facilitate the body’s immune response as well as overall cellular homeostasis.⁴ 

Monocytes are unique in their ability to carry out their function as they move throughout the bloodstream till they come across foreign microorganisms, in which they fulfil their function via characterisation. They are characterised by way of several cell receptors, some examples depicted in Fig. 1. Two core pathways of enabling immune responses against foreign microorganisms are macrophage-associated phagocytosis and dendritic cell-mediated antigen presentation.

Figure 1: Depiction of monocyte characterisation via cell surface receptors, highlighting some receptors. The key monocyte-associated functions, macrophage-associated phagocytosis and dendritic cell-mediated antigen presentation, are illustrated alongside monocytes, functions in wound healing, interactions with coagulation cascades and inflammatory response regulation (Taken from Mangaonkar et al).²

Dendritic cells support monocytes in identifying affected tissues by using toll-like receptors to expose the antigens on foreign organisms to other immune system cells. Macrophages, however, directly kill organisms and are frontline fighters against malignant cells. It is these monocytes that, in collaboration with other white blood cells, remove dead cells and facilitate the body’s immune response by signalling and informing other cells that there is an infection. The various white blood cells are able to band together and fend off the infection.^2,5

The foreign microorganisms, antigens, are also known as PAMPS (pathogen-associated molecular patterns), and upon their recognition by the receptors of the dendritic cells, the immune system is stimulated, and this stimuli results in the monocyte infiltration of the affected tissues within 12 to 24 hours.⁶ The Infiltration of the affected sites is enabled via the collaboration with the endothelial cell surface molecules and the monocytes.

Phagocytosis:

• Only specialised cells (professional phagocytes) can efficiently and effectively carry out phagocytosis
• As it is found in varying cells, it is a key player in tissue homeostasis
• The process involves only particles larger than 0.5 μm
• Alongside monocytes, other professional phagocytes are macrophages, neutrophils and dendritic cells
• These cells all have several receptors that enable their function of phagocytosis
• In summary, the process by which phagocytosis occurs is as follows:
  • Apprehension of the particle to be ingested
  • Upon apprehension, the process of internalization is activated (this being the “engulfing” like action commonly known to phagocytosis
  • Formation of a new phagosome occurs, this being a specialised vacuole (container of sorts)
  • The maturation of the phagosome leads to its transformation into a phagolysosome, this having the ability to break down the ingested particle⁷

Antigen presentation

• Dendritic cells are the most potent antigen-presenting cells, and they play a crucial role in adaptive immunity
• A myeloid precursor in monocytes is what leads to their development into dendritic antigen-presenting cells based on the specific environmental surroundings²
• In summary, the process by which antigen presentation occurs is as follows:
  • Antigens from microorganisms such as pathogens or dead cells are captured by the cells via varying methods, including phagocytosis
  • Uptaken antigens are then broken down internally into fragmented peptides encapsulated in endosomes or phagosomes. Following this, further breakdown occurs in phagolysosomes
  • The fragments are then loaded onto Major Histocompatibility Complex (MHC) molecules, with differing MHC classes representing the type of antigens they present to other immune system cells
  • Dendritic cells then migrate to lymph nodes, where they present antigen-MHC complexes to T cells, allowing for the activation of T cells
  • Activated T cells then proliferate and differentiate into effector T cells, thus commencing adaptive immune responses⁸

Highlighting the origins and characterisations of monocytes and its varying pathways of foreign microorganism and pathogenic and dead cell isolation and break down as well as some insight into its role in immune response and cellular homeostasis was to ease your mind of the concern of monocytosis itself.

How can you be diagnosed with monocytosis?

A high monocyte level alone is not enough for the diagnosis of a health issue, as multiple possible health issues can lead to high monocyte levels. As aforementioned, in cases of prolonged high levels, such as chronic monocytosis, concern is largely due to the symptoms experienced via underlying health concerns like autoimmune diseases rather than the monocyte levels themselves. In short, think of a high monocyte level positively; if anything, it serves the purpose of alerting yourself and doctors of something else amiss in your body.

But there remains an important question: If there are any symptoms of monocytosis, then how does a healthcare professional diagnose it? Well, there are a few ways for your healthcare provider to provide a diagnosis and some treatments along with it:

• Completing a blood count (CBC): This can help doctors count how many blood cells there are in your blood, and see if it falls in the normal ratio of 0.3 or less.No matter to whom or where you go the primary step in the diagnosis of monocytosis and in turn why you have it is a count of blood cells in a blood sample. For example, in the case of a blood sample providing a complete blood count with a monocyte: lymphocyte ratio greater than 0.8-1.0, where the normal ratio is 0.3 or less, relays both monocytosis and the specific link to tuberculosis as a prognosis^3,9
• Peripheral blood smear: This test is used with the knowledge that monocytosis is already taking place and helps narrow down the list of potential problems. A blood sample is examined under a microscope, and the cells’ size and shape are examined
• Absolute monocyte count: Similar to the complete blood count, this test focuses directly on the number of monocytes in your blood sample. An absolute monocyte count is based on multiplying the percentage of monocytes from your CBC by the overall number of white blood cells, thus revealing whether the count of monocytes is normal, high, or low³

It is important to note that spleen, liver, and lymph node checks are completely normal, as your healthcare professional may desire to observe if they are larger than normal. These are also not the only tests that may be conducted; based on the initial findings, more tests may need to be carried out to identify the cause of monocytosis.

Summary

• In summary, understanding the differentiation between acute and chronic monocytosis is key for proper diagnosis and treatment
• Acute monocytosis is typically a short-term response to minor infection or inflammation
• Chronic monocytosis is typically long-term and an indicator of a more serious underlying health concern, such as tuberculosis or an autoimmune disease, such as lupus
• Awareness and timely medical intervention can be crucial to improving the outcomes and symptoms of individuals dealing with monocytosis

FAQs

What are monocytes?

 Monocytes are white blood cells that play an important role in fighting infection, immune response and overall cellular homeostasis.

Can monocytosis be a sign of cancer?

Chronic monocytosis can sometimes indicate hematologic cancers, for example, leukaemia. It is important, therefore, to consult a healthcare professional for an accurate diagnosis.

How is monocytosis diagnosed?

Diagnosis of monocytosis is via blood tests like complete blood counts (CBC), for example. Further testes may be required by your healthcare professional to determine the specific cause and possible underlying health condition.

Is monocytosis common?

Monocytosis is relatively rare compared to other blood cell abnormalities, however, it can occur in both acute and chronic forms, depending on the underlying health condition.