Acute and long-term effects of booster immunisation on frequencies of antigen-specific memory B-lymphocytes

In search for a parameter that is predictive of long-term immunity, we analysed the influence of booster immunisations on frequencies of circulating memory B-lymphocytes. Specific IgG-secreting B-cells were determined by ELISPOTassay in 13 healthy adults, using diphtheria and tetanus toxoid as model antigens. Our results show that memory B-cells accumulate with every immunisation dose and remain elevated over several years. In addition. secondary B-cell responses were studied during the first 90 days after diphtheria re-immunisation. A significant indirect correlation was found between the number of previous boosters and the magnitude of specific B-cell expansion. In contrast, effects of booster immunisations did not correlate likewise with antigen-specific serology. Hence. this study illustrates that frequencies of antigen-specific B-lymphocytes can be used as an indirect measure for immunological memory. This parameter could be helpful to find scientifically based immunisation strategies for currently available and novel vaccines. (C) 2001 Elsevier Science Ltd. All rights reserved.