Serum HLA class I levels in elderly humans: Utilization in following the response to influenza vaccine

Abstract

Some healthy elderly people (30%–40%) do not respond to influenza vaccination. Subjects who respond to influenza vaccination show a significant increase in serum HLA class I levels 2 weeks after immunization. In the present study, serum HLA class I levels were measured prior to vaccination and 4 and 6 weeks after vaccination. The responders (HAI titers ⩾ 40) had higher prevaccination HLA class I levels (2.03 ± 0.12 μg/ml) than nonresponders (HAI titers < 40) (1.57 ± 0.14 μg/ml) ( P = 0.03). The responders' sHLA levels remained stable at 4 (1.98 ± 0.12 μg/ml) and 6 (2.13 ± 0.12 μg/ml) weeks postvaccination. In contrast, nonresponders' sHLA levels increased at 4 weeks (1.85 ± 0.18 μg/ml) but declined to prevaccination levels at 6 weeks (1.59 ± 0.16 μg/ml). Lymphocytes isolated from the responders ( n = 4) 4 weeks after vaccination had a higher in vitro proliferative response (mean SI = 20) than lympocytes from nonresponders ( n = 4, mean SI = 6.4) to the influenza vaccine. This proliferative response was significantly inhibited (mean SI = 6.3, P = 0.04) in the responders by the addition of an anti-HLA class I mAb and was associated with increased cell surface expression of HLA class I molecules. Two forms of sHLA class I molecules of relative mass of M r 42,000 and 40,000 were immunoprecipitated from the serum of nonresponders whereas only the M r 40,000 form was detected in the sera of young controls and of elderly responders. Our results show that in vivo antibody response correlates with in vitro lymphocyte proliferative response to influenza vaccine and that response to vaccination is associated with increased serum and cell surface expression of HLA class I. These findings suggest that the ability of elderly people to respond to vaccination can be assessed by measuring HLA class I expression.