Platelet count, temperature and pH value differentially affect hemostatic and immunomodulatory functions of platelets.

Platelets are primarily recognized for their role in hemostasis, but also regulate immune responses by interacting with leukocytes. Their highly sensitive nature enables platelets to rapidly respond to micro-environmental changes, which is crucial under physiological condition but can jeopardize in vitro analyses. Thus, we tested how platelet count and changes in pH and temperatures, which are commonly experienced during inflammation and infection but also affected by ex vivo analyses, influence platelet-leukocyte interaction and immunomodulation. Reducing platelet count by up to 90 % slightly decreased platelet activation and platelet-leukocyte aggregate formation, but did not affect CD11b activation nor CD62L shedding of monocytes or neutrophils. Acidosis (pH 6.9) slightly elevated platelet degranulation and binding to innate leukocytes, though pH changes did not modulate leukocyte activation. While platelet responsiveness was higher at room temperature than at 37 °C, incubation temperature did not affect platelet-leukocyte aggregate formation. In contrast, platelet-mediated CD11b activation and CD62L expression increased with temperature. Our data thus demonstrate the importance of standardized protocols for sample preparation and assay procedure to obtain comparable data. Further, unspecific physiologic responses such as thrombocytopenia, acidosis or temperature changes may contribute to platelet dysfunction and altered platelet-mediated immunomodulation in inflammatory and infectious disease.