Oedema disease (OD) in piglets is one of the most important pathologies, as it causes significant losses due to the high mortality because of the Shiga toxin family, which producesEscherichia coli(STEC) strains. The main toxin responsible for the characteristic pathologies in pigs is Shiga toxin 2 subtype e (Stx2e). Moreover, there is growing evidence that Stx’s family of toxins also targets immune cells. Therefore, this study evaluated the effect of different concentrations of Stx2e on porcine immune cells. Porcine peripheral blood mononuclear cells were pre-incubated with Stx2e, at three different concentrations (final concentrations of 10, 500, and 5000 CD50/mL) and with a negative control group. Cells were then stimulated with polyclonal mitogens: concanavalin A, phytohemagglutinin, pokeweed mitogen, or lipopolysaccharides. Cell proliferation was assessed by BrdU (or EdU) incorporation into newly created DNA. The activation of the lymphocyte subsets was assessed by the detection of CD25, using flow cytometry. The toxin significantly decreased mitogen-driven proliferation activity, and the effect was partially dose-dependent, with a significant impact on both T and B populations. The percentage of CD25+ cells was slightly lower in the presence of Stx2e in all the defined T cell subpopulations (CD4+, CD8+, and γδTCR+)—in a dose-dependent manner. B cells seemed to be the most affected populations. The negative effects of different concentrations of Stx2e on the immune cells in this study may explain the negative impact of the subclinical course of OD.