Binding-inhibitory antibodies suggest that the recombinant proteins had a structure resembling the native 3-D configuration, in which the critical binding epitopes were exposed in the correct conformation. with protection and a measure of vaccine potential. Methods. Cbased analysis was performed of the PvRBP reticulocyte-binding properties and binding-inhibitory activity of specific anti-PvRBP2c/PvRBP1a human antibodies. Results. PvRBP2c and PvRBP1a displayed a distinct reticulocyte-binding specificity, and their specific reticulocyte-binding domains were mapped within their N-terminal regions. Importantly, naturally acquired antibodies against the reticulocyte-binding domains efficaciously blocked reticulocyte binding of native PvRBPs, suggesting that the human immune Rabbit Polyclonal to ADRB2 system produced functional binding-inhibitory antibodies through exposure to vivax malaria. Conclusions. Reticulocyte-binding domains of PvRBP2c/PvRBP1a are targets of naturally acquired binding-inhibitory antibodies, substantiating their promise as candidate antigens against which vaccine-inducible immunity could potentially be boosted CZ415 through natural infections. Keywords: vivax malaria, reticulocyte-binding proteins, binding-inhibitory antibodies, naturally acquired immunity, vaccines. Summary The reticulocyte-specific binding domains of proteins, PvRBP2c and PvRBP1a are targets of naturally acquired binding-inhibitory human antibodies, thus substantiating their promise as candidate antigens for the development of novel malaria vaccines. malaria has remained largely neglected despite its being geographically more widespread than falciparum malaria and responsible for enormous morbidity CZ415 across the tropics [1C4]. To eliminate malaria, it is crucial to develop effective intervention strategies to counter and in this regard a potent vaccine would be a highly effective tool in combating the disease. An encouraging aspect for vaccine development is that malaria induces naturally acquired immunity (NAI) that confers disease CZ415 protection [5, 6]. NAI is known to restrict blood-stage parasite densities leading to lower incidences of clinical and severe malaria [5, 6]. A good understanding of NAI could provide key insights on the immune correlates of protection, which would immensely benefit vaccine development. Acquisition of NAI against occurs more rapidly than for irrespective of the transmission intensity [5]. Mechanisms underlying this rapid NAI acquisition remains poorly understood and warrant further investigations. In this regard, humoral responses against blood-stage antigens constitute a critical component of NAI against vivax malaria [5, 6]. Therefore, parasite proteins involved in erythrocyte invasion are potential targets of protective immunity that need in-depth validation for their development as vaccine candidates. Unlike primarily invades only reticulocytes (young immature erythrocytes), and the molecular basis underlying reticulocyte invasion is not well understood [3, 7]. The central dogma of merozoite invasion has been its dependence on the essential interaction between the Duffy-binding protein (PvDBP) and its receptor, Duffy antigen receptor for chemokines (DARC) [8, 9], which does not account for reticulocyte specificity because DARC is present on both normocytes and reticulocytes. reticulocyte specificity (Belem strain) was first reported to be mediated by 2 reticulocyte-binding proteins (PvRBPs), PvRBP1a and PvRBP2c [10]. Thereafter, the has evolved Duffy-independent, redundant invasion pathways [12C14]. It is thus critical to elucidate the molecular basis of merozoite invasion. PvRBPs are implicated to play crucial roles in mediating reticulocyte specificity and may play a role in Duffy-independent invasion. Therefore, PvRBPs are attractive candidate antigens for the development of vivax vaccines and warrant further validation. The lack of in vitro culture has deferred in-depth dissection of vivax antigens [3, 7]. In the interim, PvRBP homologues known as reticulocyte binding-like homologous (PfRH) proteins were discovered in invasion inhibition assays, binding inhibition is an important surrogate for evaluating vaccine potential of antigens [23]. This is the first report to demonstrate the functionality of naturally acquired human antibodies targeting PvRBPs, which has major implications for the development of vivax malaria vaccines. MATERIALS AND METHODS Sample Collection and Ethics Approvals infections. Peripheral blood samples were collected from human subjects via finger prick after informed consent. infections were diagnosed using a rapid diagnostic test (SD Bioline Malaria Antigen Pf/Pv, Bio Standard Diagnostics, India) and confirmed microscopically by examination of Giemsa-stained thin blood smears. Blood samples (2C5 mL) were collected from 66 parasites and human plasma samples for our studies were obtained from this source of 66 human blood.