The complex functions of mast cells in chronic human liver diseases.

Mast cells (MCs) are multifunctional effector cells of the immune system. MCs were originally thought to be involved in IgE-associated immediate hypersensitivity and allergic disorders, but it is now known that they contain or elaborate an array of mediators with a multitude of effects on many other cells. A number of studies have found that MCs are involved in various liver diseases. Although still controversial, they seem to be involved in the liver's fibrotic response to chronic inflammation and parasitic infection. Hepatic fibrosis is the most frequent liver response to toxic, infectious, or metabolic agents. During the establishment of this pathological condition, there is an increase in the components of the basement membrane that leads to continuous basement membrane-like structures being raised within Disse's space and a decrease in the number of sinusoid endothelial fenestrae. This leads to a complex process called "sinusoidal capillarization." At the cellular level, liver fibrogenesis is initiated by hepatocyte necrosis, which induces the recruitment of a large number of inflammatory cells, including MCs, which can be considered the primary effectors of the process changing sinusoidal endothelial cells into capillary-type endothelial cells. We review the roles played by MCs in hepatic chronic diseases and describe a biopsy section of hepatic tissue taken from a patient with chronic C virus-related hepatitis showing diffuse sinusoidal capillarization and a high density of MCs. This observation has led us to hypothesize a relationship between these highly specialized cells and sinusoidal capillarization.