From the Guidelines
Monocytes are a type of white blood cell that plays a crucial role in the immune system, characterized by their large size, single nucleus, and ability to differentiate into macrophages or dendritic cells, as supported by the most recent study 1. They are an essential part of the body's first line of defense against infections and play a key role in the inflammatory response. Monocytes typically make up about 2-8% of the total white blood cell count in healthy adults and can be identified by their positivity for CD14 and intermediate intensity for CD45, as noted in an earlier study 1. Some key features of monocytes include:
- Their ability to transform into macrophages or dendritic cells when an infection or tissue damage occurs
- Their role in engulfing and digesting pathogens, dead cells, and foreign substances through phagocytosis
- Their production of cytokines, which are signaling molecules that coordinate the activities of other immune cells
- Their presentation of antigens to T cells, helping to activate the adaptive immune response
- Their potential to indicate various conditions, including infections, inflammatory disorders, certain cancers, and autoimmune diseases, when their counts are abnormal, as discussed in a recent study 1. It is worth noting that monocytes can be distinguished from other myeloid cells, such as neutrophils, by their specific markers and functional characteristics, as highlighted in a study on myeloid-derived suppressor cells 1. Overall, monocytes are a vital component of the immune system, and their functions and characteristics are essential for maintaining immune homeostasis and responding to pathogens and tissue damage.
From the Research
Definition and Function of Monocytes
- Monocytes are white blood cells that belong to the mononuclear phagocyte system, deriving from precursors in bone marrow 2.
- They have a half-life of 1-2 days in blood before migrating into various tissues 2.
- Monocytes are the progenitors of monocyte-derived macrophages and play a crucial role in seeding tissues with sufficient macrophages to replace loss from infection and tissue damage 3.
- They contribute to the overall orchestration of immunity, possessing direct protective and pathogenic activities 3.
Role of Monocytes in Immune System
- Monocytes are important cell types of the innate immune system, defending the host from intruding microbial pathogens 4.
- They contribute to the pathogenesis and progression of diseases such as liver fibrosis, atherosclerosis, multiple sclerosis, and tumor metastasis 4.
- Monocytes and monocyte-derived macrophages also play a beneficial role in liver fibrosis regression, muscle regeneration, and clearance of β-amyloid plaques in Alzheimer's disease 4.
Monocyte Subsets and Heterogeneity
- Monocytes are a heterogeneous cell population with differences in size, phenotype, and function 5.
- There are several subsets of monocytes, including classical, intermediate, and non-classical monocytes, which have been characterized in detail in health and disease 2.
- The subset classification applies to other species as well, but there are important differences in subset-specific gene expression between species 2.
- Monocyte heterogeneity has consequences for monocyte-derived immune cells, including dendritic cells, macrophages, and osteoclasts 5.
Monocyte Conversion and Plasticity
- Monocytes are mobilized from the bone marrow and recruited to sites of inflammation, where they carry out their respective functions in promoting inflammation or facilitating tissue repair 6.
- There are 2 subsets of monocytes in mice (3 subsets in humans) that are converted during inflammation and injury, highlighting the plasticity of monocyte subsets 6.