Increased serum HLA class I molecule levels in elderly human responders to influenza vaccination

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Abstract
Increased cell surface expression and serum levels of HLA class I molecules have been shown to occur in normal elderly humans. Elderly subjects (65 years and older) generally also have a poorer response to influenza vaccine than younger adults. Some 30 to 40% of elderly subjects do not respond to influenza vaccination. Sera from 20 elderly subjects with a positive response to influenza vaccine (HAI antibody titer > 40) and 20 subjects who did not respond (HAI antibody titer < 40) were randomly selected and the levels of soluble HLA class I molecules determined before and after vaccination. The subjects who responded had higher serum HLA class I levels both before and after vaccination than did non-responders. Two weeks after vaccination non-responders showed similar serum HLA class I levels (1.78 mg/ml +/- 0.62) as compared to prevaccination levels (1.73 mg/ml +/- 0.49). The responders showed significantly higher levels of soluble HLA class I molecules following vaccination (2.64 mg/ml +/- 0.99) as compared to pre-vaccination (2.08 mg/ml +/- 0.85, p = 0.00001). Our results suggest that measuring soluble HLA class I molecules in the serum may be useful in assessing the adequacy of response to influenza vaccination in the elderly population.