FIG. 4.

PsaA-, PspA-, PspC-, and PdB-specific T helper 2 cytokine secretion by antigen-stimulated CD4⁺ T cells following pneumococcal carriage. Mice were intranasally challenged with ≈7.5 × 10⁶ CFU of Streptococcus pneumoniae EF3030 in 15 μl of Ringer's solution; 28 days postinfection, spleen-, lung-, and cervical lymph node-derived CD4⁺ T cells were purified and cultured with 5 μg of PsaA, PspA, PspC, or PdB per ml for 5 days in complete medium. Cytokine levels in culture supernatants were determined by ELISA capable of detecting >20 pg/ml of IL-4 or IL-10. The data presented are the mean cytokine concentrations ± standard error of the mean. Naïve mice displayed responses that were below the detection limit of the ELISA and are not shown. Asterisks indicate significant differences (P < 0.05) between the maximum and next highest antigen-specific CD4⁺ T-cell cytokine response from infected mice.