Sarcoidosis and Sjögren's Syndrome: A Comparison of Salivary Protein Profiles

Sarcoidosis (Sarc) and Sjögren's syndrome (SS) are two different diseases that may affect the exocrine glands and cause similar clinical signs and symptoms. Both diseases may coexist complicating the diagnosis. Previous studies have suggested that immobilized pH gradient gel electrophoresis (IPG) shows a unique protein band P4.25 that is useful for the diagnosis of SS. Objective: The purpose of this study was to investigate the possibility of using IPG electrophoresis to differentiate between Sarc and SS. Methods: Stimulated parotid saliva was collected from 24 patients with confirmed diagnosis of either Sarc or SS (12 Sarc & 12 SS). Salivary flow rate (sFR) was determined gravimetrically and total salivary protein (TP) was determined using the BCA method. Salivary protein electrophoresis, IPG (pI 3.5-5.0), was performed using the Pharmacia LKB Multiphor II electrophoresis system according to the manufacturer instructions. Protein profiles were compared between the two groups. Statistical analyses were performed using one-way ANOVA to compare differences in the mean of age, sFR, and TP. Chi square test was used to compare differences in the frequency of P4.25 between the groups. Results: Each patients group consisted of 9 females and 3 males (4 Caucasians and 8 African Americans). The mean age for Sarc was 52.8 + 3.9 years (mean + SEM) and 57.0 + 3.0 years for SS. The mean sFR for Sarc was 0.41+0.07 ml/min /gland and 0.43+0.07 ml/min/gland for SS. TP was 130.0+29.2 mg% for Sarc and 104.0+8.8 mg% for SS. P4.25 was present with equal frequency (9/12) for both Sarc and SS. No statistical differences were observed in the age, sFR, TP, or the frequency of P4.25 between Sarc and SS, (p = 0.506, p=0.768, p = 0.718, p = 1.000, respectively). Conclusions: Immobilized pH gradient gel electrophoresis (IPG) is not useful to differentiate between Sarc and SS.