Evidence that the reduced number of natural killer cells in type 1 (insulin-dependent) diabetes may be genetically determined.

Viruses may cause Type 1 (insulin-dependent) diabetes. We wondered whether the number and function of natural killer cells, which are important in anti-viral defense, are disturbed in diabetic patients. We studied 16 recently diagnosed Type 1 diabetic patients, 18 Type 1 diabetic patients diagnosed more than 15 years previously, 18 Type 2 (non-insulin-dependent) diabetic patients and 23 control subjects. We determined the number of natural killer cells (expressed as log10%) using anti-Leu 11 monoclonal antibody and the function (in log10 lytic units) concurrently using a 51Cr release assay with K562 as target cells. We found that the number of natural killer cells was reduced in Type 1 diabetes (1.01 +/- 0.04) as compared with Type 2 diabetic patients (1.16 +/- 0.04, p = 0.004) and normal control subjects (1.16 +/- 0.04, p = 0.006). To establish whether the reduced natural killer cell number is genetically determined we studied 19 identical twin pairs discordant for Type 1 diabetes; we found that even the non-diabetic co-twins had a reduced natural killer cell number (0.93 +/- 0.05, p = 0.0006) as compared with normal control subjects. Natural killer cell function was similar in all groups while natural killer activity per cell was significantly increased in the recently diagnosed diabetic patients (1.63 +/- 0.07) as compared with long-standing diabetic patients (1.26 +/- 0.26, p = 0.03) and controls subjects (1.36 +/- 0.07, p = 0.006). In conclusion the reduced number of natural killer cells in Type 1 diabetes appears to be genetically determined while their activity at diagnosis is increased.