Synchronous Decline of Serum-Soluble HLA Class I Antigen and β-Cell Function in Insulin-Dependent Diabetes Mellitus

Abstract Serum-soluble HLA class I molecules (sHLA) have immunomodulatory functions and their serum levels correlate with the HLA class I phenotype. We studied longitudinal changes of serum sHLA levels in insulin-dependent diabetes mellitus (IDDM). A total of 198 serum samples were obtained from 40 IDDM patients before and after IDDM onset. sHLA was assayed by a sandwich ELISA. sHLA levels in IDDM patients at the initiation of insulin therapy (IDDM onset) were markedly reduced compared with those in normal controls (334.2 ± 26.3 ng/ml vs 492.4 ± 55.5 ng/ml, mean ± SEM, P = 0.0038). They fell sharply during 6 months before and after the onset of IDDM. The dynamic profile of sHLA and the time course of β-cell loss were different between IDDM patients with and without HLA-A24. In those with HLA-A24, sHLA became significantly lower than normal controls with HLA-A24 at IDDM onset. Recovery of their sHLA values occurred at 3 years from IDDM onset. On the other hand, in those without HLA-A24, sHLA levels began to decrease since the onset of IDDM and became significantly lower than normal controls without HLA-A24 at 4 years after the onset. Recovery of sHLA occurred at more than 6 years from the onset. An early (within 18 months), complete loss of β-cell function occurred in 5 of 13 IDDM patients with HLA-A24 compared with 1 of 14 of those without HLA-A24 ( P = 0.077). A late (more than 36 months after the onset of IDDM), complete loss of β-cell function occurred in 7 of 14 IDDM patients without HLA-A24 but in none of 13 of those with HLA-A24 ( P = 0.0058). These results indicate that the decline of sHLA is synchronous with massive β-cell destruction, and that these events occur during a short period in IDDM patients with HLA-A24, whereas they occur during a relatively long period in those without HLA-A24.