Figure 3Aiii-iv shows that the proportion of such O-iRBCs progressively increased in the perfusate, reflecting an active pitting process. The pitting rate per transit through isolated-perfused spleens 0. On Giemsa-stained histologic sections, uninfected RBCs were observed as they squeezed to cross the sinus walls from the cords to the sinus lumen Figure 3Bi-ii. Pitting of Art-iRBCs was also observed by immunochemistry using a human convalescent serum, with the immunoglobulins detected by alkaline-phosphatase-labeled anti-human Ig antibodies Figure 3E.
On Giemsa-stained sections of the spleen, dead parasite remnants appeared as brown dots either within intact Art-iRBCs intraerythrocytic dead parasite remnants or outside RBCs extraerythrocytic dead parasite remnants Figure 4A,Dii. This confirmed that the brown dots observed on sections of Art-iRBC-perfused spleens were attributable to dead parasite remnants. Extraerythrocytic dead parasite remnants accounted for Fragmentation of extracellular Art-iRBCs was very rarely observed. Taken together, these data strongly suggest that direct phagocytosis of intact Art-iRBCs by macrophages took place in isolated-perfused spleens, a process leading to intramacrophagic dead parasite remnants Figure 2Cid,Ciid.
Analysis of the localization of extraerythrocytic dead parasite remnants see Figure 4Dii for definitions showed that Only 4. Kinetics and morphologic aspects of pitting. On Giemsa-stained histologic sections, uninfected RBCs were observed as they squeezed to cross the sinus walls Bi-ii from cords co to sinus lumens sl.
Some DPRs retained in the sinus wall were still linked to their once-host cell by a string-like formation Dii and incompletely pitted Art-iRBCs were observed in sinus lumens, with a membrane-bound DPR in contact with a luminal cell Diii-iv. E Aspect of pitting as observed by immunochemistry using a human convalescent serum, the Ig being detected by alkaline-phosphatase labeled reagent. Specific microcirculatory structures of the perifollicular zone, namely small blood-filled spaces densely packed with erythrocytes in the proximity of a proportion of lymphoid nodules as well as cords and sinus lumens of the red pulp were readily identified on Giemsa-stained histologic sections Figure 4Di.
Processing of Art-iRBCs was also more efficient in the red pulp than in the perifollicular zone. Of interest, predominant Art-iRBC retention and processing in the red pulp strongly confirm the suitable quality of the perfusion of this peculiar zone in isolated-perfused spleens. Art-iRBC retention and processing.
A-B Aspect and quantification of brown dots on Giemsa-stained sections showing that they correspond to dead parasite remnants. Most extraerythrocytic dead parasite remnants colocalized with cord cells A,Dii. Ci-ii Aspect and localization of Art-iRBCs and extraerythrocytic dead parasite remnants at a cellular scale, analyzed either by Giemsa-staining Ci or by immunohistochemistry Cii. To adjust for circulatory space on each field, dead parasite remnants numbers are expressed as mean and standard error of the mean for RBCs in each zone Diii. Exploring the abdominal, prone-to-bleed, difficult-to-sample human spleen has often resembled studying a black box.
The quantitative readout for the clearing function of the isolated-perfused human spleens provided results in close similarity with in vivo data obtained from malaria patients in terms of clearance kinetics, qualitative tissular processing, and pitting rate Figure 2 ; Table 1.
This clearing function is impaired when the spleen is absent or not functional.
Their 2- to 5-day life span is shorter than that of normal noninfected red blood cells. Functional clearance of Art-iRBCs by the isolated-perfused spleen indicates that the organ retains clearing and processing functions and thus that the black box can now be informatively opened for hypothesis-driven tissue investigations. The zone dependence of Art-iRBC retention Figure 4 is in keeping with the classic paradigm that RBC quality control is more a function of the slow microcirculation of the red pulp than of the fast microcirculation of the perifollicular zone.
The accumulation of Art-iRBCs in the red pulp might be interpreted as a purely rheologic filtration similar to that observed with carbonized plastic beads. Taken together, our clearing and processing data confirm that pitting of Art-iRBCs is an intrasplenic process in humans, the remnant being removed as the RBC crosses the wall of red pulp sinuses. It is tempting to speculate that most extraerythrocytic dead parasite remnants observed into or in close proximity to the sinus wall were generated by pitting, while cordal dead parasite remnants were created by phagocytosis of intact Art-iRBCs.
This latter aspect is reminiscent of the physiologic clearance of senescent RBCs, which is handled through elimination of intact RBCs rather than lysed debris. Of importance, Art-iRBC clearance observed here—either through phagocytosis or pitting—did not require any significant spleen priming and was independent from most serum factors, since perfusion was performed in Krebs-human albumin medium. We used P falciparum -infected RBCs as markers for spleen filtering functions.
In return, human isolated-perfused spleens may now help explore the pathogenesis of P falciparum malaria, the most frequent and severe health problem in which the spleen plays a central role.
The experimental challenge of human isolated-perfused spleens with circulating blood stage parasites along with defined effectors should lead to a better understanding of the mechanisms of naturally acquired protection and to identification of their target antigens. This novel tool fills a gap in malaria vaccine development in providing a relevant functional assay for erythrocytic-stage parasite clearance that may help prioritize vaccine development efforts. Developing the erythrocytic-stage component of the envisioned multistage antimalaria vaccine would greatly benefit from a functional screening model equivalent to the human sporozoite challenge for the pre-erythrocytic vaccine development.
This is, however, difficult to monitor in phase 2 vaccine trials as, for ethical reasons, even a minimal P falciparum parasitemia in patients or volunteers must be promptly treated. The clearance of damaged, aging, or genetically variant RBCs as well as sequestration crisis in sickle cell disease or red cell removal in hemolytic eg, autoimmune anemias are examples of physiologic or pathologic mechanisms that could be explored using this new tool.
The publication costs of this article were defrayed in part by page charge payment. We reserve a special mention to Dr Nathalie Chabbert for creative input at crucial steps of this project. Sign In or Create an Account. User Tools. Sign In. Content Menu. Close Introduction. Patients, materials, and methods. Article Navigation.
Ex vivo perfusion of human spleens maintains clearing and processing functions Pierre A. Buffet Pierre A. This Site. Google Scholar. Valentine Brousse Valentine Brousse.
Bertrand Dousset Bertrand Dousset. Anne Couvelard Anne Couvelard. Reza Kianmanesh Reza Kianmanesh. Olivier Farges Olivier Farges. Alain Sauvanet Alain Sauvanet. Catherine Ottone Catherine Ottone. Huot Khun Huot Khun. Laurence Fiette Laurence Fiette. Ghislaine Guigon Ghislaine Guigon.
Michel Huerre Michel Huerre. Peter H. David Peter H. Blood 9 : Article history Submitted:. Figure 1. View large Download PPT. Table 1. Figure 2. Figure 3.
Figure 4. An Inside Blood analysis of this article appears at the front of this issue. The authors have no conflicting financial interests. Mebius RE, Kraal G. Structure and function of the spleen. Nat Rev Immunol. Sickle-cell disease. Laparoscopic splenectomy for autoimmune hemolytic anemia in patients with chronic lymphocytic leukemia: a case series and review of the literature. Am J Hematol. Wyler DJ. The spleen in malaria. In: Malaria and the red cell. Parasite sequestration in Plasmodium falciparum malaria: spleen and antibody modulation of cytoadherence of infected erythrocytes.
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