Figure 4

CD4⁺ T cells produce low ex vivo levels of IFN-γ, TNF-α, and IL-2 in response to S. suis systemic infection.

Mice were infected intraperitoneally with a dose of 5 × 10⁷ CFU of S. suis wild-type strain P1/7 (n = 3 per group × 3 individual experimental infections). Spleens were harvested 6 h post-infection and total splenocytes plated at 5 × 10⁶ cells/well. After 6 h of incubation, gentamycin was added to the culture to prevent cell toxicity. Non-stimulated cells from mock-infected animals served as negative control for basal expression (C−). Cells stimulated with Concanavalin A (0.1 μg/ml) were used as positive control (C+). Total splenocytes were incubated for 48 h. Brefeldin A (3 μg/ml) was added during the last 5 h of incubation and CD4⁺ T cells were MACS-isolated from the culture, stained intracellularly for different cytokines and analyzed by FACS. Data are expressed as mean ± SEM (in % of positive cells) from 3 individual experimental infections. FACS was performed using a FACSCalibur instrument. Twenty thousand gated events were acquired per sample and data analysis was performed using CellQuest software. *P < 0.05, indicates statistically significant difference compared to negative control cells (C−).