Cold Mechanical Isolation of Placental Macrophages as a Method to Limit Procedure-Induced Activation of Macrophages

Isolation of placental macrophages using enzymatic digestion at warm temperatures is widely used for in vitro studies. However, studies in brain and kidney tissue show that this method activates immune cells, immediate early genes, and heat shock proteins. Isolating placental macrophages while preserving their tissue-specific characteristics as much as possible is pivotal to reliably studying their functions. We therefore developed a mechanical dissociation protocol at low temperatures and compared this to enzymatic digestion at high temperatures. Decidual and villous macrophages were isolated from term human placentas. A cell suspension was generated by mechanical dissociation using a gentleMACS. For warm enzymatic digestion, Accutase was added, followed by incubation at 37°C. Macrophages were isolated after Ficoll density gradient centrifugation. Cell types were analyzed with flow cytometry (CD45, CD14, CD80, CD86, CD163, and CD206) and their activation status with real-time PCR (FOS, JUN, HSP27, HSP70, IL1β, TNFα, IL10, and TGFβ) after cell sorting. A higher proportion of leukocytes and macrophages was obtained from the villi with cold mechanical dissociation (p < 0.05). Compared to warm enzymatic digestion, cold mechanical dissociation resulted in a higher expression of CD163 in villous and decidual macrophages (p < 0.05). Warm enzymatic digestion showed higher levels of TNFα, IL1β, and IL10 in decidual and villous macrophages, and HSP70 in villous macrophages. Our data show that mechanical dissociation of placental tissue at low temperatures is associated with less activation of placental macrophages. This suggests that cold mechanical dissociation is a preferred method, resulting in macrophages that more closely resemble their in-tissue state.