Iccosomes and the secondary antibody response.

Iccosomes derived from follicular dendritic cells (FDC) are believed to play an important role in dispersion of antigen necessary for induction of anamnestic responses. Because FDC are aberrant and iccosome release has not been observed in aged mice, we hypothesized that these animals would be impaired in their ability to mount anamnestic responses. To test this, anamnestic responses were compared in aged and control mice. To ensure the presence of functional lymphocytes, some aged mice were reconstituted with T- and B-memory cells obtained from control mice. Anamnestic responses in aged mice were markedly depressed even when given functional memory cells. To more directly relate the impaired antibody response of aged mice to FDC function, antigen-bearing FDC from either aged or control mice were incubated with T- and B-memory cells from control mice to induce an anamnestic response. Antigen retained by FDC from aged mice was much less immunogenic than antigen retained by FDC from control mice. Since iccosome formation does not appear in aged mice, iccosome-like fragments were generated by sonicating FDC from aged mice and tested for their ability to induce an anamnestic response. This procedure restored the ability of antigen retained on FDC from aged mice to induce a normal anamnestic response. These data support the concept that the inability to form and disperse iccosomes contributes to the impaired ability of aged mice to mount anamnestic antibody responses and provides further support for the role of iccosomes in anamnestic responses.