Kongsomboonvech Angel K, Scally Stephen W, Le Guen Yann, Valissery Praveesh, Salinas Nichole D, Cowman Alan F, Tolia Niraj H, Egan Elizabeth S
Department of Pediatrics, Stanford University School of Medicine, Stanford, CA.
The Walter and Eliza Hall Institute of Medical Research, Parkville, Australia.
bioRxiv. 2025 Jul 30:2025.07.30.667750. doi: 10.1101/2025.07.30.667750.
The ability of the malaria parasite to invade and replicate asexually within human red blood cells (RBCs) is central to its pathogenicity, accounting for hundreds of thousands of deaths each year. RBC invasion is a multi-step process involving several host-parasite interactions, yet the host factors acting during invasion remain underexplored, largely due to the intractability of mature enucleated RBCs. The transmembrane protein CD44 was identified as a host factor for invasion through a forward genetic screen using genetically modified RBCs derived from primary human hematopoietic stem cells. Here, we identify an anti-CD44 monoclonal antibody, BRIC 222, that significantly promotes invasion, and demonstrate that its effect is mediated through CD44 cross-linking. CD44 cross-linking induced changes in the phosphorylation of RBC cytoskeletal proteins, consistent with a proposed role for CD44 as a co-receptor during invasion. CD44 cross-linking also altered the RBC membrane, increasing the accessibility of several surface proteins, including the essential invasion receptor Basigin. The parasite ligand Erythrocyte Binding Antigen-175 (EBA-175), which interacts with CD44, enhanced invasion and induced RBC membrane changes similarly to BRIC 222. Moreover, both BRIC 222 and EBA-175 increased binding of the PfRH5/PCRCR invasion complex to Basigin, an interaction known to be essential for invasion. We propose that CD44 cross-linking, potentially by EBA-175, serves to coordinate and enhance downstream ligand-receptor interactions and to promote signaling to the host cell cytoskeleton, making RBCs more permissive to invasion.
疟原虫在人类红细胞（RBC）内无性侵入和复制的能力是其致病性的核心，每年导致数十万人死亡。红细胞入侵是一个多步骤过程，涉及多种宿主-寄生虫相互作用，但入侵过程中起作用的宿主因素仍未得到充分研究，这主要是由于成熟无核红细胞难以处理。通过使用源自原代人类造血干细胞的基因改造红细胞进行正向遗传筛选，跨膜蛋白CD44被鉴定为入侵的宿主因子。在这里，我们鉴定出一种抗CD44单克隆抗体BRIC 222，它能显著促进入侵，并证明其作用是通过CD44交联介导的。CD44交联诱导了红细胞细胞骨架蛋白磷酸化的变化，这与CD44在入侵过程中作为共受体的作用一致。CD44交联还改变了红细胞膜，增加了几种表面蛋白的可及性，包括必需的入侵受体疟原虫结合素。与CD44相互作用的寄生虫配体红细胞结合抗原175（EBA-175），与BRIC 222类似，增强了入侵并诱导了红细胞膜变化。此外，BRIC 222和EBA-175都增加了PfRH5/PCRCR入侵复合物与疟原虫结合素的结合，已知这种相互作用对入侵至关重要。我们提出，可能由EBA-175介导的CD44交联，有助于协调和增强下游配体-受体相互作用，并促进向宿主细胞细胞骨架的信号传导，使红细胞更易于被入侵。
