monosyyttit

Monosyyttit, known in English as monocytes, are a type of white blood cell and a central component of the innate immune system. They are produced in the bone marrow from hematopoietic stem cells through precursor cells such as monoblasts and promonocytes, circulate in the bloodstream, and migrate into tissues where they differentiate into macrophages or dendritic cells.

Function and subsets: In blood, monosyyttit patrol for signs of infection and injury, phagocytose pathogens and debris, secrete cytokines, and present antigens to T cells via MHC class II molecules. In tissues they differentiate into macrophages or dendritic cells, taking on specialized roles according to the local environment. In humans there are several subsets, commonly described as classical CD14++CD16-, non-classical CD14+CD16++, and intermediate CD14++CD16+; these subsets differ in pattern of chemokine receptors (such as CCR2 and CX3CR1) and functional responses.

Physiology and lifespan: Monosyyttit represent about 2-8% of circulating leukocytes. They typically circulate for about one to three days before migrating into tissues, where they can survive longer as tissue macrophages or dendritic cells.

Clinical relevance: Abnormal monosyyttit levels can occur with infection, chronic inflammatory diseases, autoimmune disorders, or myeloproliferative conditions. Monocytes play a role in atherosclerosis through differentiation into macrophages in vessel walls and lipid uptake. Therapeutic strategies occasionally target monocyte recruitment or activation.

See also: Monocytes, Macrophages, Dendritic cells.