Silica and the immune system.

This article collects the evidence that shows that the biological reactions to Silica are due to the stimulation of the Immune System. Both Innate and Adaptive Immunity are involved. The following sets of events take place sequentially: (1) Silica is recognized as a PAMP (pathogen-associated molecular pattern) by the Receptors of Innate Immunity; (2) This causes the stimulation first and then the death of the key cells of Innate Immunity (the macrophages); (3) While stimulated, macrophages produce cytokines (IL-1 and TNF) that stimulate fibroblasts; (4) The same and possibly other cytokines produced by silica- activated macrophages induce the maturation of dendritic cells, which are the connecting elements between the Innate and the Adaptive (lymphoid) Immune Systems; (5) It follows a polyclonal activation of the Adaptive Immunity; (6) The end result is the formation of fibro-hyaline tissue. In view of the double involvement of the Innate and the Adaptive Immune Systems and their cooperation in the stimulation of fibrosis, Silicosis can be considered as a "Collagen" Disease, related to other diseases of that group like Rheumatoid Arthritis, Lupus erythematosus and Scleroderma. Not surprisingly the incidence of these Diseases has been shown to be significantly increased in human exposed to Silica.