Hb SS blood may contain reticulocytes with an increased amount of CD36 expression on their membranes, allowing platelets to form a bridge between these young sickle cells and endothelial cells in post-capillary venules. This initial slowdown of blood flow creates an environment in which cells containing Hb SS can easily form sickled cells.
The rigid cells, which are formed as a result of the sickling process, can collect in and plug small blood vessels. This can then cause tissue damage and organ infarction. In addition, the polymerized hemoglobin is thought to disrupt the RBC membrane, exposing phosphatidylserine that can trigger hemostasis.
Subsequently, white blood cells (WBCs) may adhere to endothelium in response to recruitment in the inflammatory process. This leads to further occlusion as neutrophils capture additional RBCs in the post-capillary venules.
Contributing further to vaso-occlusion is the decreased level of L-arginine in patients with SCD. L-arginine is a substrate needed to produce nitric oxide (NO). NO has vasodilatory properties as well as anti-inflammatory and anti-platelet properties. Thus a decrease in NO may lead to increased cellular adherence to endothelium.
