**4. Pathogenesis**

The pathogenesis of SS remains to be definitively determined. Three possible pathogenical mechanisms have been considered, but none of them have been consistently demostrated (Requena, 2007): a) a type III hypersensitivity reaction, b) an activation of T cells by antigens or superantigens, and c) a disturbance of neutrophils´ function. It seems that genetic factors play a role since SS has been associated to several HLA, especially to Bw54 (Mizoguchi, 1988). Because of female predominace in parainflammatory and idiopathic cases and both pregnancy and contraconceptive pills implication in some cases of SS, hormonal background can also be involved in the development of SS.

Numerous cytokines are involved in the pathogenesis of this condition, including interleukins 1, 2, 3, 6, and 8 and gamma interferon, but the key substance is the granulocytecolony stimulating factor (G-CSF). The administration of G-CSF can result in an outbreak of SS and this substance is elevated in serum of patients with SS and its levels are directly related with the disease activity (Kawakami et al, 2004; Ginarte & Toribio, 2010).
