Kinetics, localization and isotype profile of antibody responses to immune stimulating complexes (iscoms) containing human influenza virus envelope glycoproteins.

The immune stimulating complex (iscom) is a particulate adjuvant formulation combining multimeric presentation of antigen with a built-in adjuvant, Quillaja saponin. Iscoms induce strong serum antibody responses that are readily boosted. To further characterize this property of iscoms, the development and maturation of primary and secondary antibody responses to iscoms containing influenza virus antigen were investigated, in serum by ELISA and on single B-cell level by ELISPOT. After a single subcutaneous injection, B cells secreting antigen-specific IgG (IgG-SC) were primarily observed in the draining lymph nodes (LN), showing peak numbers at day 7 which then declined rapidly. Serum IgG levels, as well as IgG-SC in the spleen, persisted for several weeks and, with time, IgG-SC cells also appeared in the bone marrow (BM). These results suggest that the IgG response to iscoms initially is located to the LN but that IgG-SC are redistributed with time and may persist for a long time in other organs, including the spleen and BM. Moreover, a booster dramatically enhanced the frequency of IgG-SC in LN, spleen and BM suggesting that iscoms induce a potent B-cell memory. Comparisons of antibody responses to iscoms with those to influenza virus antigen in Freund's complete adjuvant, TiterMax or aluminium hydroxide suggest that the choice of adjuvant influences both the magnitude, kinetics, localization and isotype profile of antibody responses.