Systemic sclerosis (SSc) or scleroderma is an autoimmune connective tissue disease. The pathogenesis of SSc is unclear. Microvascular dysfunction is an early and prominent component along with endothelial-fibroblast interactions promoting disease progression. Autoantibodies are found in the majority of SSc patients, which include anti endothelial cell antibodies (AECA). This study is designed to investigate the role of AECA in the pathogenesis of SSc, and characterise the intracellular signalling cascades activated when AECA bind to endothelial cells. Cell based enzyme linked immunosorbent assays (ELISAs) were used to screen SSc patient serum samples (n=60) to detect antibodies (IgG) that bind to human umbilical vein endothelial cells (HUVEC) and human dermal microvascular endothelial cells (HMEC). ELISAs were also used to detect any consequent increase in leukocyte adhesion molecules, including E-selectin, ICAM-1 and VCAM following pretreatment with SSc samples. These ELISAs were optimised using interleukin-1 beta (IL-1β, 10ng/ml, n=6 per adhesion molecule), before using SSc patient serum samples. 22 SSc samples, but not normal serum or IgG, caused an increase in leukocyte adhesion molecules and showed a high level of AECA binding. IgG was isolated by column chromatography from SSc serum samples with a high AECA titre, and also showed an upregulation of leukocyte adhesion molecules (n=6). Lipopolysaccharide contamination was ruled out by showing that responses were insensitive to polymyxin B. Real time reverse transcription polymerase chain reaction (RT-PCR) was also conducted, using HUVEC stimulated over a time course with IL-1b. A peak of mRNA expression was seen at 4-6 hours with E-selectin (4-fold increase), ICAM-1 (55-fold), VCAM (6-fold) and MCP-1 (7-fold), when normalised against 28S RNA (representative data). In initial experiments (n=2) patient samples caused a similar pattern of increases in mRNA. In preliminary experiments (n=2) Western blots have been used to detect p42/p44 MAP kinase activation in HUVEC and HMEC, using IL-1β and AECA in whole serum, and purified IgG from SSc patients. These show activation at 15 and 30 minutes after stimulation. Other signalling pathways are being investigated including p38 MAP kinase and pSAPK/JNK.