From the Guidelines
Monocytosis is most commonly caused by infections such as Salmonella, which is an intracellular pathogen that can lead to a monocyte predominance in the blood count 146. When considering the potential causes of monocytosis, it is essential to evaluate the patient's overall clinical presentation and laboratory results.
- Bacterial infections, including Salmonella, can cause an increase in monocyte counts, as these cells play a crucial role in engulfing and eliminating pathogens 146.
- The total white blood cell count and differential can provide valuable information in diagnosing the underlying cause of monocytosis, with a monocyte predominance suggesting the presence of an intracellular pathogen 146.
- Other infections, such as viral or parasitic etiologies, may also lead to changes in the white blood cell count, including an increase in monocytes, although the evidence is less clear 67, 62.
- In clinical practice, it is essential to consider the most recent and highest quality evidence when evaluating the cause of monocytosis, and Salmonella infection is a well-established cause of monocytosis, as indicated by the 2017 Infectious Diseases Society of America clinical practice guidelines 1.
From the Research
Infections Causing Monocytosis
- Monocytosis, or elevated monocytes, can be caused by various infections, including: + Mycobacterium tuberculosis infection, as evidenced by studies 2, 3, 4, 5 + TB-HIV co-infection, which poses a challenge to human survival and complicates every aspect of TB, including presentation, diagnosis, and treatment 6
- These infections can lead to changes in monocyte phenotype and function, contributing to immunopathology and disease progression
Monocyte Subsets and Tuberculosis
- Classical monocytes expressing inflammatory mediators increase as tuberculosis disease progresses 4
- Non-classical monocytes expressing molecules associated with anti-pathogen infection are progressively depleted as the disease progresses 4
- The differentiation trajectory of monocytes from classical to intermediate to non-classical subsets is abnormal in tuberculosis, with CEBPB and CORO1A identified as genes potentially related to TB development 4
Impact of Infections on Monocytes
- Mycobacterium tuberculosis infection can induce changes in monocyte subsets, including increased expression of CD40, CD64, and PD-L1 in monocytes from tuberculosis patients 2
- The plasma milieu in tuberculosis patients can affect monocyte phenotype and function, with potential implications for immunopathology and disease progression 2, 3