CD28 is required for the CpG-ODN–induced expansion of CD4⁺and CD8⁺ T cells.

C57BL/6 mice and CD28^−/− mice underwent 9 daily injections of CpG-ODN or Neg-ODN. One day after the last ODN injection, the draining axillary lymph nodes (A) and spleens (B) were harvested and analyzed by flow cytometry. The total numbers of naive/unactivated (CD44^low) and memory/activated (CD44^high) CD4⁺/CD3⁺ and CD8⁺/CD3⁺T cells, unactivated (CD80^low) or activated (CD80^high) CD19⁺ B cells, and unactivated (CD80^low) or activated (CD80^high) CD11c⁺ dendritic cells for each group were estimated. The total cell numbers in each organ were evaluated via trypan blue exclusion of viable cells on a hemocytometer. The total cell yield for each subset was calculated by multiplying the proportion of the corresponding group by the total number of live cells obtained per organ. The error bars represent the standard error of the means obtained from 3 separate experiments.