The activation of T cells is mediated through T cell receptors (TCR), and this activation can be modulated by killer immunoglobulin-like receptors (KIR) [3,4]. KIR are members of the immunoglobulin superfamily and are expressed on natural killer (NK)

cells and subsets of T cells. Depending on their structure, they can generate activating or inhibitory signals [5]. Inhibitory KIR molecules bind to target cell major histocompatibility complex (MHC) class I molecules and prevent the Ferrostatin-1 attack of NK cells on normal cells [5]. The capacity to attack self cells that lack expression of MHC class I molecules is known as ‘missing self recognition’[6,7]. The missing-self hypothesis has been supported by several independent findings demonstrating that allotypic MHC products actually protect cells from lysis by NK lymphocytes, apparently by delivering negative signals that inhibit NK cell cytotoxic

function [7]. On the other hand, when an activating KIR binds to its ligand, activating signals are generated leading to the kill of the target cells. Besides the modulation of TCR-mediated activation of T cells, KIR expression may affect the role Fulvestrant in vitro of NK cells in autoimmune diseases, where these cells may exert a pathogenic function through inappropriate activation or suppression function through lysis of dendritic cells or activated T cells [5]. Therefore, genes that control KIR expression may possibly influence normal and pathological immune responses. To date, 17 KIR genes and pseudogenes have been described on human chromosome 19q13.4 (∼0·7 Mb) [8]. Eight genes that encode KIR receptors are inhibitory (2DL1, 2DL2, 2DL3, 2DL5A, 2DL5B 3DL1, 3DL2 and 3DL3), seven are activating (2DL4, 2DS1, 2DS2, 2DS3, 2DS4, 2DS5, 2DS5 and 3DS1) and two are pseudogenes (2DP1 and 3DP1). Of these, four KIR genes are always present: 3DL3, 3DP1, 2DL4 and 3DL2. They are considered framework genes [9]. A previous study Histone demethylase by Momot et al.[10] suggested that the presence of KIR2DS2+, in the absence of KIR2DL2-, is associated with SSc. In contrast, Pellet

et al.[11] found association of the disease with the presence of KIR2DS1 and the absence of KIR2DS2. Given these contradictory results, we designed a study to investigate further the association of KIR genes with systemic sclerosis. One hundred and ten patients with systemic sclerosis were evaluated prospectively in the out-patient clinic of the Service of Rheumatology at the Hospital de Clínicas de Porto Alegre. All patients met the American College of Rheumatology (ACR) criteria for SSc [12] or the criteria suggested by LeRoy and Medsger for diagnosis of early forms of SSc [13]. All patients were Brazilian (92 women and 18 men; 81·8% European descendents and 18·2% African descendents) and most of them lived in the metropolitan area of Porto Alegre/RS. There were neither individuals of Asiatic origin nor Amerindians among the patients. Patients with overlapping syndromes were excluded.