Biomechanics of red blood cells in human spleen and consequences for physiology and disease
Significance The 3D opening of the interendothelial slit in human spleen creates a physical fitness test for red blood cells (RBCs) and clears them from circulation if their geometry and deformability are altered. We present a unique computational framework for the development of prognostic markers for diseases that alter RBC physical characteristics and identify quantitative limits for splenic slit clearance. Our work shows how the splenic slit determines distributions of size and shape of healthy RBCs. Our work lays the groundwork for systematic reconstruction of RBC navigation in the human spleen with consequences for a variety of acute and chronic medical conditions associated with hereditary alterations of RBCs, infectious diseases, and cancers. Red blood cells (RBCs) can be cleared from circulation when alterations in their size, shape, and deformability are detected. This function is modulated by the spleen specific structure of the interendothelial slit (IES) Here, we present a unique physiological framework for development of prognostic markers in RBC diseases by quantifying biophysical limits for RBCs to pass through the IES, using computational simulations based on dissipative particle dynamics. The results show that the spleen selects RBCs for continued circulation based on their geometry, consistent with prior in vivo observations. A companion analysis provides critical bounds relating surface area and volume for healthy RBCs beyond which the RBCs fail the "physical fitness test" to pass through the IES, supporting independent experiments. Our results suggest that the spleen plays an important role in determining distributions of size and shape of healthy RBCs. Because mechanical retention of infected RBC impacts malaria pathogenesis, we studied key biophysical parameters for RBCs infected with Plasmodium falciparum as they cross the IES. In agreement with experimental results, surface area loss of an infected RBC is found to be a more important determinant of splenic retention than its membrane stiffness. The simulations provide insights into the effects of pressure gradient across the IES on RBC retention. By providing quantitative biophysical limits for RBCs to pass through the IES, the narrowest circulatory bottleneck in the spleen, our results offer a broad approach for developing quantitative markers for diseases such as hereditary spherocytosis, thalassemia, and malaria.
Proceedings of the National Academy of Sciences