Human Spleen Microvascular Endothelial Cells

CD14^dim/CD16⁺⁺ Monocytes Induce VWF:Ag Release from Splenic ECs, in vitro

Desmopressin (DDAVP) treats bleeding disorders by releasing von Willebrand factor (VWF), but its mechanism is unclear as endothelial AVPR2 receptors remain undemonstrated. The spleen, a major FVIII-producing organ with distinct monocyte reservoirs, may mediate this effect. Salarilak et al. examined a splenectomised haemophilia patient with impaired DDAVP response, then used in vitro co-culture experiments to assess VWF release from DDAVP-treated human splenic endothelial cells (HSECs) with different monocyte subtypes.

Neonatal and adult HSECs co-produced FVIII and VWF (~0.2 mU/cm² FVIII:C and 3 mU/cm² VWF:Ag in 48-h supernatants up to passage 4), declining thereafter until FVIII:C was undetectable at passage 6. Confluent HSECs in monoculture or co-culture with PBMCs, classical (CD14/CD^16-), or non-classical (CD14^dim/CD16) monocytes were treated with 100 ng/ml DDAVP for 1 h. DDAVP did not induce VWF or P-selectin release compared to untreated cells, while PMA significantly induced VWF:Ag release. Proximity of PBMCs or classical monocytes did not influence this. However, direct exposure of CD14^dim/CD16⁺⁺ monocytes to HSECs enabled DDAVP to significantly increase VWF:Ag in supernatants.

As platelet-activating factor (PAF) was proposed as a potential signal transmitter from CD14^dim/CD16⁺⁺ monocytes, HSECs were treated with pure PAF (12 ng/ml-40 μg/ml). Neither PAF nor DDAVP induced VWF:Ag release, while PMA remained effective, suggesting PAF alone does not mediate the monocyte-driven DDAVP effect.