Plasmodium sporozoites can invade hepatocytic cells independently of the Ephrin receptor A2

Abstract

Sporozoite forms of the malaria parasite Plasmodium are transmitted by mosquitoes and first infect the liver for an initial round of replication before parasite proliferation in the blood. The molecular mechanisms involved during sporozoite invasion of hepatocytes remain poorly understood. In previous studies, two receptors of the Hepatitis C virus (HCV), the tetraspanin CD81 and the Scavenger Receptor BI (SR-BI), were shown to play an important role during entry of Plasmodium sporozoites into hepatocytic cells. In contrast to HCV entry, which requires both CD81 and SR-BI together with additional host factors, CD81 and SR-BI operate independently during malaria liver infection, as sporozoites can use CD81 and/or SR-BI, depending on the Plasmodium species, to invade hepatocytes. However, the molecular function of CD81 and SR-BI during parasite entry remains unknown. Another HCV entry factor, the Ephrin receptor A2 (EphA2), was recently reported to play a key role as a host cell entry factor during malaria liver infection. Here, we investigated the contribution of EphA2 during CD81-dependent and SR-BI-dependent sporozoite infection. Using small interfering RNA (siRNA) and antibodies against EphA2, combined with direct detection of parasites by flow cytometry or microscopy, we show that blocking EphA2 has no significant impact on P. yoelii or P. berghei host cell infection, irrespective of the entry route. Thus, our findings argue against an important role of EphA2 during malaria liver infection.

Important Extracellular Interactions between Plasmodium Sporozoites and Host Cells Required for Infection

“…Together with other data, these findings supported the conclusion that EPHA2 was important for sporozoite invasion [82]. Recent studies using siRNA to knockdown EPHA2 expression in hepatocytes and similar antibody inhibition studies, however, did not support a role for EPHA2 in hepatocyte invasion for either P. yoelii or P. berghei [83]. EPHA2 knockdown appeared to have no clear effect on sporozoite invasion regardless of the hepatocyte source, and antibodies to EPHA2 showed no greater ability to inhibit sporozoite invasion compared to the control [83].…”

“…Recent studies using siRNA to knockdown EPHA2 expression in hepatocytes and similar antibody inhibition studies, however, did not support a role for EPHA2 in hepatocyte invasion for either P. yoelii or P. berghei [83]. EPHA2 knockdown appeared to have no clear effect on sporozoite invasion regardless of the hepatocyte source, and antibodies to EPHA2 showed no greater ability to inhibit sporozoite invasion compared to the control [83]. In light of these conflicting results, the precise role of EPHA2 in sporozoite invasion remains an open question.…”

The Micronemal Plasmodium Proteins P36 and P52 Act in Concert to Establish the Replication-Permissive Compartment Within Infected Hepatocytes

“…All three host cell receptors are required for productive invasion to various degrees and, in the case of EphA2 and CD81, for PVM formation (Kaushansky et al, 2015 ; Manzoni et al, 2017 ). However, the contribution of EphA2 in these processes was brought into question in a recent study based mainly on the reduction of EphA2 expression levels using siRNAs (Langlois et al, 2018 ). The findings presented here show for the first time that both P36 and P52 are individually necessary for the formation of the replication-permissive PVM, that P36 is localized (and frequently co-localized with P52) in the sporozoite micronemes and subsequently secreted, and that both proteins form a complex in sporozoites.…”

Emerging Roles for Eph Receptors and Ephrin Ligands in Immunity

“…A clear role for Ephs as viral entry receptors has been shown for Nipah and Hendra viruses (ephrin-B2 and ephrin-B3) (172, 173), Kaposi's sarcoma-associated herpesvirus (EphA2) (70, 174), and Epstein-Barr virus (EphA4 and EphA2) (76, 138, 140). Similarly, it was also recently described that the sporozoite stage of the Plasmodium parasite, the causative agent of malaria, engages EphA2 on liver hepatocytes in order to establish a productive infection (135) although additional entry receptors may be involved in this process as well (175). EphA2 is also used by the fungal pathogen Cryptococcus neoformans to traverse the blood-brain barrier in order to gain entry into the brain (137).…”