Abstract
Immunodeficient mouse–human chimeras provide a powerful approach to study host specific pathogens like Plasmodium (P.) falciparum that causes human malaria. Existing mouse models of P. falciparum infection require repeated injections of human red blood cells (RBCs). In addition, clodronate lipsomes and anti-neutrophil antibodies are injected to suppress the clearance of human RBCs by the residual immune system of the immunodeficient mice. Engraftment of NOD-scid Il2rg-/- mice with human hematopoietic stem cells leads to reconstitution of human immune cells. Although human B cell reconstitution is robust and T cell reconstitution is reasonable in the recipient mice, human RBC reconstitution is generally poor or undetectable. The poor reconstitution is mainly the result of a deficiency of appropriate human cytokines that are necessary for the development and maintenance of these cell lineages. Delivery of plasmid DNA encoding human erythropoietin and interleukin-3 into humanized mice by hydrodynamic tail-vein injection resulted in significantly enhanced reconstitution of erythrocytes. With this improved humanized mouse, here we show that P. falciparum infects de novo generated human RBCs, develops into schizonts and causes successive reinvasion. We also show that different parasite strains exhibit variation in their ability to infect these humanized mice. Parasites could be detected by nested PCR in the blood samples of humanized mice infected with P. falciparum K1 and HB3 strains for 3 cycles, whereas in other strains such as 3D7, DD2, 7G8, FCR3 and W2mef parasites could only be detected for 1 cycle. In vivo adaptation of K1 strain further improves the infection efficiency and parasites can be detected by microscopy for 3 cycles. The parasitemia ranges between 0.13 and 0.25% at the first cycle of infection, falls between 0.08 and 0.15% at the second cycle, and drops to barely detectable levels at the third cycle of infection. Compared to existing mouse models, our model generates human RBCs de novo and does not require the treatment of mice with immunomodulators.
Highlights
Malaria is caused by parasites of the Plasmodium species which are transmitted by infected Anopheles mosquitoes
Reticulocytes account for 10 to 30% of human red blood cells (RBCs) as measured by staining the blood cells with anti-glycophorin antibodies and thiozol orange (S1 Fig). 100 μl of whole blood from these mice were used for ex vivo infection with 1x106 mature P. falciparum schizonts (3D7 strain)
In the in vivo adaptation process, initial parasite clearance and reappearance after a period of time is observed. These results are in agreement with a previous report [20] and this may be due to the retention of majority of the infected RBCs in the sinus cord of the spleen [21, 22]
Summary
Malaria is caused by parasites of the Plasmodium species which are transmitted by infected Anopheles mosquitoes. Plasmodium species are host specific, making it difficult to model human parasite infection in laboratory animals. The requirements to inject large volumes of human RBCs repeatedly along with treating mice with anti-neutrophil antibody and clodronate liposomes to suppress the rapid clearance of the injected human RBCs by macrophages makes this a difficult system to work with [7]. P. falciparum infection was reported in NSG mice without the use of clodronate liposomes or anti-neutrophil antibody, but still requiring daily human RBC injection [9]. The best small animal model for malaria infection so far is the human RBC-supplemented, immune cell-optimized humanized (or RICH) mice that support multiple cycles of P. falciparum infection in the presence of a human immune system [10]. It is still a formidable challenge to establish a malaria infection model that does not require regular human RBC supplementation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
