High serum levels of soluble CD8 in insulin-dependent diabetes.

In type 1 (insulin-dependent) diabetes mellitus (IDDM) CD8+ T cells represent the majority of lymphocytes which infiltrate the pancreatic islets during beta cell destruction. Soluble CD8 antigen (sCD8) has been shown to correlate with CD8 cell subset activation. In this study we measured by ELISA sCD8 levels in sera from: 33 newly diagnosed IDDM patients; 29 type 1 diabetics with duration of disease more than 1 year; 37 healthy siblings of IDDM patients; 19 healthy controls. Sera from both groups of IDDM patients and from healthy siblings exhibited soluble CD8 mean levels significantly higher than controls (P = 0.0001, P < 0.003, P < 0.03 respectively). Soluble CD8 levels above the normal range (mean +/- 2 s.d. of controls) were found in a percentage of newly diagnosed subjects (54.5%) significantly higher than in subjects with a long-standing duration of disease (6.9%, P < 0.0005) and healthy siblings (16.2%, P < 0.002). Our results suggest that the raised levels of soluble CD8 near to diabetes onset may indicate the activation of CD8+ T cells probably responsible for the autoimmune beta cell destruction.