Introduction

Monocytosis is known for the higher number of monocytes present in the circulation of blood. Monocytes are a type of leukocyte, (also known as white blood cells) present in the body that defend our immune system from infectious substances. The levels of monocytes in the blood depend upon age, and different medical conditions or diseases, such as autoimmune diseases or pregnancy. Monocytosis doesn’t always present with specific symptoms but may be associated with swelling, fatigue or weakness.¹

Understanding monocytosis

The role of monocytes in the immune system

The immune system is composed of the innate immune system and the adaptive immune system. The innate immune system is the initial response of the body to pathogens, it is rapid but does not form a memory of the antigens. The adaptive immune system is the second line of defence in the immune system, and although slower, remembers the antigens on pathogens. 

White blood cells, or leukocytes, are produced in the bone marrow and form both types of immune systems. Monocytes are part of the innate immune system. They circulate in the blood for roughly 1 to 3 days before migrating into various tissues throughout the body. In the tissues, they develop into macrophages and dendritic cells, which are important participants in the immune response. 

The roles of monocytes are: 

• Antigen presentation- monocytes process and deliver antigens (labels on pathogens) to T-cells (a type of white blood cell called a lymphocyte) to initiate adaptive immune response 
• Tissue repair and remodelling - help in healing wounds and remodelling the tissues with the help of secreting factors and enzymes to repair damage 
• Phagocytosis - helps to clear cancer cells, foreign substances, microbes etc by engulfing other cells or particles⁴ 

Diagnosis and symptoms of monocytosis

The following symptoms are associated with monocytosis,  

• Fatigue
• Weakness
• Fever
• Weight loss
• Swelling 

Monocytosis can be identified by the routine blood tests, such as: 

• Absolute Monocyte Count (AMC) - this blood test can identify the level of monocytes in the blood that are above the normal threshold, which is between 0.2 to 0.8 x 10⁹ /L 
• Complete Blood Count (CBC) - this blood test counts the number of blood cells, including red blood cells and white blood cells in your sample 
• Relative Monocyte Count - monocytes make up 2-10% of total leukocytes, and a relative increase can lead to monocytosis

Monocytosis is often caused by another condition, such as an infection, inflammatory and autoimmune diseases, hematologic disorders and cancer. Therefore, diagnosing the cause of monocytosis may involve a broad range of tests depending on the individual’s symptoms and medical history. 

Causes of monocytosis

The causes of monocytosis include: 

• Infectious diseases - monocytosis usually reacts to infections or foreign substances present in the body such as bacterial, viral or parasitic infections and recovery from acute infections
• Inflammatory and autoimmune conditions - it is associated with rheumatoid arthritis, inflammatory bowel disease and systemic lupus erythematosus
• Hematologic disorders - chronic myelomonocytic leukaemia is a rare blood cancer defined as the increase in monocytes due to dysfunctional blood cells⁵ 
• Malignancies - it is associated with solid tumours i.e. ovarian and lung cancers and lymphomas including hodgkin’s lymphoma, which increase monocytes 
• Stress- physical and emotional 
• Medications and their side effects, such as corticosteroids  
• Post-splenectomy 

Monocytosis is a sign of an underlying illness, and determining the cause is critical for proper therapy and care.

Monocytosis in the elderly

Due to increases in life expectancy, an increasing elderly population are experiencing frequent chronic diseases, which can lead to monocytosis. As we age, our immune system undergoes immunosenescence, modifying the function of immune cells like monocytes. This can lead to an increase in the number of monocytes, causing a higher baseline of monocytes compared to younger individuals. In addition, elderly people have more chances of chronic diseases or infections which could lead to an increase in levels of monocytes, such as atherosclerosis and chronic obstructive pulmonary disease (COPD).² 

Potential implications for health and disease management

Monocytosis can have consequences for elderly people, which influence the treatment and healthcare approach. Here are some implications for monocytosis which could be an indicator in elderly with the underlying conditions like autoimmune diseases, infections, inflammation, chronic diseases, function of the immune system and cancers (such as myelodysplastic syndromes). Healthcare professionals could diagnose and treat these conditions, examine disease advancement and modify interventions to enhance a good life for elderly patients.³ 

Age-related changes in the immune system

Immunosenescence and its impact on immunity

Immunosenescence refers to the slow degradation of the immune system that occurs with age. This process impacts both the innate and adaptive immune systems. Immunosenescence causes a variety of modifications that impair immune response function and efficacy.⁶ 

The impact on innate immunity are: 

• Monocyte function - due to ageing, there are changes in the function of the body as the circulation of monocytes increases which leads to chronic inflammation 
• Cytokine production - elderly people have different production of cytokine which leads to secretion of pro-inflammatory cytokines. This persistent inflammatory condition may worsen the course of age-related illnesses
• Phagocytic activity - with age, monocytes and macrophages decrease which reduces the capability to clear pathogen and foreign substances   

The impact on adaptive immunity are: 

• T-cell dysfunction - Ageing reduces the generation of T-cells, and existing T-cells show depletion and diminished ability to proliferate
• B-cell changes - production of B-cells (a second type of lymphocyte) declines with age, affecting the capacity to react to new antigens and lowering the efficiency of vaccines in the elderly

Monocytosis itself can increase the risk of infections, leading to respiratory infection in the elderly, causing pneumonia and influenza. The urinary tract infection is due to age and changes in the tract that weaken the immune response. The herpes zoster infection reactivates the viruses due to a decrease in immunity. There are chances of chronic diseases like cardiovascular, type 2 diabetes, neurodegenerative and cancer.  

Management and treatment

Treating underlying causes 

Infectious diseases 

• Antibiotic therapy - this therapy cures bacterial infections such as tuberculosis 
• Antiviral treatments- the treatment cures viral infections like Epstein-Barr Virus EBV and Cytomegalovirus CMV 
• Antifungal treatments- used to treat fungal infections such as Aspergillosis

Inflammatory and autoimmune conditions 

• Immunosuppressive therapies -  these therapies include corticosteroids which help to decrease inflammation ie in inflammatory bowel disease 
• Disease-modifying antirheumatic drugs (DMARDs) - treat rheumatoid arthritis⁷

Hematologic disorders and malignancies 

• Chemotherapy and radiation - chronic myelomonocytic leukaemia is managed by chemotherapy agents like hydroxyurea 
• Targeted therapies and immunotherapies - utilize genetic mutations linked with malignancies

Symptomatic management 

Management of monocytosis depends on the underlying cause, which may involve supportive care and preventive measures such as: 

• Managing the pain of the patients with chronic pain of cancer and rheumatoid arthritis to reduce the pain. 
• Nutritional support to achieve a balanced diet 
• Counseling and mental health services 
• To manage the patient's symptoms and quality of life including symptoms of breathlessness, pain, nausea and psychological support⁸

Conclusion

Monocytosis is an abnormally high level of monocytes in the blood, which ia more common in the elderly. It can be a sign of illness such as infectious infections, inflammatory and autoimmune problems, hematologic abnormalities, and malignancies. Addressing the underlying cause is essential in order to provide specialised treatments such as antibiotics, immunosuppressive medicines, and targeted cancer treatments.. Future study is critical to better understanding the pathophysiology of monocytosis in the elderly, opening the way for advances in diagnostic approaches and the creation of more effective, personalized treatment regimens. Increased attention to the special requirements of older people may result in enhanced quality of life and reduced morbidity associated with this illness.