Group B Streptococcus Induces a Robust IFN-γ Response by CD4⁺ T Cells in an In Vitro and In Vivo Model

Figure 5

In vivo CD4⁺ T cell contribution to cytokine production during primary and secondary GBS infections. C57BL/6 mice were injected intraperitoneally with a dose of 10⁶ CFU of wild-type GBS serotype III strain COH-1. Surviving animals who had previously displayed clinical signs were boosted with a second dose of 10⁶ CFU of GBS strain COH-1 two weeks after initial infection. Spleens of animals with clinical signs and positive bacteremia were harvested 96 h after primary infection or 48 h after boost infection ( per group × 5 individual experimental infections). Five hours prior to spleen collection, mice were injected with Brefeldin A (200 μg). (−) Control animals were similarly treated. Splenic CD4⁺ T cells were MACS-purified, stained intracellularly for different cytokines, and analyzed by FACS. Representative data from 5 different experimental infections. Cytokine basal expression levels in (−) control animals were similar at 96 h after primary mock-infection and 48 h after secondary mock-infection. Representative histograms from the latter time point were selected for the figure. Twenty thousand gated events were acquired per sample and data analysis was performed using CellQuest software. Histograms were drawn based on PE-control stain and were plotted on logarithmic scales. It should be noted that isotype controls are the same in both groups, but only displayed on left panels to simplify the figure.