Isolation and expression of UB05, a Plasmodium falciparum antigen recognised by antibodies from semi-immune adults in a high transmission endemic area of the Cameroonian rainforest

Abstract

Background: Antibodies in adults living in malaria endemic areas that target specific parasite antigens are implicated in protective immunity to infection and disease. This study aimed to identify, isolate and characterise targets of protective immunity in malaria. A Plasmodium falciparum antigen termed UB05 (Genbank Accession Number DQ235690: PlasmoDB PF10_ 0372) that had been isolated by immunoscreening with semi-immune sera was studied. Methods: Polymerase chain reaction, sequencing and bioinformatics were used to analyse the UB05 gene. A specific mouse anti-UB05 antibody was used in parasite reinvasion growth/inhibition assays and in immunoflourescence to localise the antigen. In a crosssectional study, enzyme linked immunosorbent assay was used to study immunoglobulin G (IgG) responses to the antigen. Results: The gene revealed significant homologies with gene sequences from Plasmodia and other apicomplexan parasites and had two alleles in the wild P. falciparum isolates. The antigen is expressed by schizonts and segmented merozoites. Mouse antibodies against it marginally inhibit in vitro invasion of erythrocytes by P. falciparum. The IgG responses to UB05 were found to be significantly lower (p-0.05) in the sera of children (2-5 years) compared with adults ()18 years), with or without parasitaemia. However, parasitaemia correlated inversely (rs0.7-0.75) with serum anti-UB05 IgG concentrations. Furthermore, anti-UB05 IgG concentrations were lower in the sera of febrile patients (body temperature

Surface Engineering of the RNA Coliphage Q? to Display Plasmodium Falciparum Derived Asexual Blood Stage Antigens UB05 and Merozoite Surface Protein 3

“…People with naturally acquired immunity to malaria produce antibodies specific to several parasite antigens which have been demonstrated to play a role in their resistance to clinical disease and parasitaemia [14,24,32,37]. In this regards protective immunity mediated especially by asexual blood stage antigens like MSP3 or UB05 could either mean just the absence of symptomatic malaria but underlying parasitaemia or the complete absence of both symptomatic malaria and parasitaemia.…”

“…Previously antibodies targeting several asexual stage antigens including the merozoite surface antigens 1 (MSP1) and 3 (MSP3), microneme proteins erythrocyte binding antigen 140 (EBA140) and 175 (EBA175) and rhoptry proteins 2 (Rh2), 5 (Rh5) and UB05 are reported to protect children (5-14 years) from clinical malaria [12][13][14].…”

“…In this study, we have chosen an approach based on the display of promising Plasmodium falciparum derived malaria antigens upon surface of the RNA coliphage Qβ for effective presentation to the immune system. The Merozoite surface protein 3 (MSP3) and UB05 are two malaria parasite blood-stage antigens validated as potential malaria vaccine candidates following analysis of their role in protective immunity in children and adults [14][15][16][17].…”

“…This is mainly because this region is not only conserved across different parasite strains [21][22][23]; but equally possessed epitopes confirmed to be targeted by antibodies associated with protection [18,23]. Similarly UB05 antigen specific immune responses have been reported as a potential marker of protective immunity against malaria [14,24,25].…”

The role played by alternative splicing in antigenic variability in human endo-parasites

“…The exact role of this protein is not known, however it appears to be a soluble protein that is exported from the parasite [32]. The P. falciparum surface antigen UB05, which is recognized by IgG antibodies from adults that are semi-immune to malaria infection [33], was found to be alternatively spliced through 3’ and 5’ alternate splicing [26,34]. Another suspected surface antigen, PF 70, is soluble in Triton X, suggesting that it is membrane bound.…”