Disulfide bonds in merozoite surface protein 1 of the malaria parasite impede efficient antigen processing and affect the in vivo antibody response

Abstract

The 19 kDa C‐terminal fragment of the malaria parasite merozoite surface protein 1 (MSP119) is a leading malaria vaccine candidate. In rodents, high antibody levels to this protein confer protective immunity, and can be generated by immunization with the antigen in adjuvants. In natural human infections, however, MSP119‐specific antibody responses can be short‐lived andcomparatively low, despite repeated exposure to infection. The tightly folded structure of MSP119 is stabilized by five or six disulfide bonds. These bonds impede antigen processing and, thereby, may affect the generation of CD4+ T cells providing help for B cells. Asparagine endopeptidase could digest unfolded, but not native MSP119 in vitro. Immunization with unfolded MSP119 resulted in a faster antibody response, and a combination of unfolded and native MSP119 increased antibody responses to the native form. Immunization with either form of the antigen activated similar numbers of CD4+ T cells, but, unlike the antibody response, CD4+ T cells immunized with one form of MSP119 were able to respond in vitro to the other form of the protein. Although the reduced form of MSP119 does not induce protective antibodies, our data suggest that inclusion of unfolded protein may improve the efficacy of MSP119 as a vaccine.See correction http://dx.doi.org/10.1002/eji.200490004

Effective induction of high-titer antibodies by viral vector vaccines

“…1c). In agreement with these data, MSP-1 19 is known to be refractory to antigen processing 8 , and the CD4 + T helper cell response against MSP-1 33 is likely to be crucial for antibody responses to MSP-1 19 .…”

Production and Preclinical Evaluation of Plasmodium falciparum MSP-1 19 and MSP-3 11 Chimeric Protein, PfMSP-Fu 24

“…MSP-1 19 is known to be poorly immunogenic, eliciting low levels of antibodies and poor T-cell activation and functional T helper cells in humans (29,31). A number of studies have shown that the addition or presence of exogenous helper T-cell epitopes provides help to B cells, thereby enhancing the immunogenicity of PfMSP-1 19 (32).…”

“…No host cell protein contamination was observed in purified PfMSP-Fu 24 , as determined by an ELISA (0.3 ng/ml [0.03%]) and by Western blotting (data not shown). The protective immune responses induced by PfMSP-1 19 have been shown to be dependent on protein conformation (31). We tested the conformational integrity of the PfMSP-1 19 component in PfMSP-Fu 24 by two conformation-sensitive MAbs, 1H4 and 2E10 (42).…”

“…PfMSP-1 19 antibodies have also been shown to correlate with naturally acquired immunity in several epidemiological studies (27). Several studies have shown that immunization with recombinant MSP-1 19 fails to produce high-titer antibodies (28)(29)(30)(31). However, inclusions of exogenous T cell epitopes have been shown to improve the immunogenicity of the PfMSP-1 19 fragment (32).…”

Monoclonal Antibodies to Esophageal Cancer–Related Gene2 Protein

“…The immunogen, designed based on the primary structure of protein which is directly or indirectly responsible for the conformation and/or accessibility of MAb epitopes, may be modified following expression in mammalian cells. (13)(14)(15)(16) Although the mechanism of this modification is unknown, at least two possibilities exist: re-arrangement of disulfide bonds (17) and phosphorylation. (18,19) ECRG2 belongs to the kazal family which contains the conservative pattern x(8)-C-x(6)-C-x(7)-C-x(6)-Yx(3)-C-x(2,3)-C-x(17)-C, and these conservative cysteines are involved in three disulfide bonds.…”