Analysis of the immune response against tetanus toxoid: Enumeration of specific T helper cells by the Elispot assay

Tetanus toxoid (IT) is an antigen known to induce strong T cell specific immune responses in humans after vaccination. Here we have used the Elispot assay to assess the number of TT specific interferon-gamma (IFN-gamma) secreting T cells present in individuals and monitored the number of TT specific T cells present in the donors for more than two years. In each of the 22 healthy volunteers tested, TT specific T cells could be detected. Six out of 7 repetitively tested donors shoved a remark-ably constant number of TT specific IFN-gamma secreting T cells over several months, whereas one donor demonstrated a transient increase during a flu-Nice infection. Three healthy donors received TT booster-immunizations and showed significant increases in the number of TT-specific IFN-gamma secreting T cells which reached peak levels by 4 weeks after vaccination. Depletion of either CD4(+) cells, CD8(+) T cells or CD16(+)/CD56(+) T cells lay immunomagnetic separation demonstrated that TT specific IFN-gamma secretion is mediated exclusively by CD4(+) T cells. In addition, HLA class-I anti -II blocking studies showed that IFN-gamma production is performed by HL class-II restricted cells. Our data show that the Elispot assay can be reliably used to assess the number of TT specific CD4(+) IFN-gamma producing cells (i.e. probably T helper cells) and therefore maybe also useful for the assessment of reactions to other helper antigens.