Systemic inflammatory response syndrome (SIRS) is recognized to be an exaggerated defense response to various stressors, including trauma. CD4+ T-regulatory cells (CD4+ Tregs) are key mediators in balancing inflammatory processes. Recent findings demonstrated that platelets and CD4+ Tregs interact after injury and SIRS. Therapeutic strategies to modulate the activation of these and other immune cells in SIRS are currently lacking. Ancrod has immunomodulatory effects on CD4+ Tregs that could be beneficial in the treatment of SIRS. Therefore, we studied the impact of ancrod on activation levels of CD4+ Tregs and CD4+ non-Tregs, platelets, and antigen-presenting cells (APC) in vitro and in vivo. We tested the in vitro effect of ancrod (0-15 IU) and the in vivo effect of 8 IU ancrod vs. saline. After collection of spleens and platelet-rich plasma of male C57Bl/6N mice, cells were isolated and incubated with ancrod for 2 hours. Furthermore, we tested the effect of stimulation. CD4+ Tregs, CD4+ non-Tregs, APC and platelet activation were analyzed by flow cytometry. Our results demonstrate that ancrod exerts selective effects on different cell populations. Ancrod affects the adaptive and innate immune responses. Furthermore, we identified a differential effect of ancrod on CD4+ Tregs versus CD4+ non-Tregs depending on the mode of cellular stimulation. Additionally, our findings suggest a dose-dependent role of ancrod in the modulation of platelet activation. Our findings provide the first evidence supporting the potential of ancrod in selectively modulating immune cells, highlighting ancrod as a promising candidate for further investigation.