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.
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 cross-sectional 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 (r=0.7- 0.75) with serum anti-UB05 IgG concentrations. Furthermore, anti-UB05 IgG concentrations were lower in the sera of febrile patients (body temperature >37.5 degrees C) than their non-febrile counterparts regardless of parasitaemia status.


CONCLUSIONS
These results are compatible with a role for UB05 in the development of immunity and as a marker of protective immunity to malaria.
Titanji
Vincent Pryde Kehdinga
VP
Department of Biochemistry and Microbiology, Faculty of Science, University of Buea, Buea, Cameroon. vpk.titanji@yahoo.com
Amambua-Ngwa
Alfred
A
Anong
Damian Nota
DN
Mbandi
Stanley Kimbeng
SK
Tangie
Emily
E
Tening
Ivo
I
Yengo
Raymond
R
D000328:Adult; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood / Q000276:immunology; D000953:Antigens, Protozoan / Q000276:immunology* / Q000378:metabolism; D001483:Base Sequence; D002163:Cameroon; D003430:Cross-Sectional Studies; D004196:Disease Outbreaks; D004797:Enzyme-Linked Immunosorbent Assay; D005998:Glycine; D006801:Humans; D008288:Malaria / Q000453:epidemiology; D051379:Mice; D008969:Molecular Sequence Data; D010802:Phylogeny; D010963:Plasmodium falciparum / Q000145:classification / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D011994:Recombinant Proteins; D005998:Glycine