Synthetic low-toxicity muramyl dipeptide and monophosphoryl lipid A replace Freund complete adjuvant in inducing growth-inhibitory antibodies to the Plasmodium falciparum major merozoite surface protein, gp195

Abstract

The Plasmodium falciparum major merozoite surface protein (gp195) is a protective antigen against lethal malaria. However, increasing evidence indicates that the efficacy of a malaria vaccine will require a strong adjuvant that is safe for human use. We compared the efficacies of two low-toxicity synthetic immunomodulators, B30-MDP (a lipophilic muramyl dipeptide derivative) and LA-15-PH (a synthetic equivalent of monophosphoryl lipid A), with that of Freund complete adjuvant (FCA) in eliciting an antibody response to gp195. Rabbits were imunized with native gp195 and B30-MDP, LA-15-PH, or the two in combination, with Uposomes as the vehicle. Aluminum hydroxide and FCA were used as reference adjuvants. Results showed that adjuvant formulations based on B30-MDP alone or in combination with LA-15-PH induced high antibody titers to gp195, as compared with FCA. LA-15-PH alone was less effective. Aluminum hydroxide induced significantly lower antibody titers. The functional activity of the rabbit anti-gp195 antibodies induced by different adjuvants was evaluated in an in vitro parasite growth inhibition assay previously shown to correlate with anti-gp195 immunity in the Aotus monkey model. AU rabbits immunized with B30-MDP-LA-15-PH and two of three rabbits immunized with B30-MDP alone produced sera that strongly inhibited parasite growth. The degree of growth inhibition was similar to that with FCA. The antibody titers of the rabbits receiving B30-MDP-LA-15-PH strongly correlated with the degree of in vitro growth inhibition. Our findings provided strong evidence that adjuvant formulations based on synthetic B30-MDP and LA-15-PH can replace FCA as adjuvants in stimulating protective inmunity specific for gp195.

Roles of conserved and allelic regions of the major merozoite surface protein (gp195) in immunity against Plasmodium falciparum

“…Thus, the ability of anti-gp195 sera to inhibit in vitro parasite growth may be indicative of a protective gp195-specific antibody response. Sera and purified immunoglobulins from rabbits immunized with gp195-CFA also efficiently inhibited parasite growth (27,28). Therefore, the ability of the rabbit anti-gp195 sera to inhibit homologous and heterologous parasites was investigated by using this in vitro inhibition assay.…”

“…ELISA. Serum anti-gp195 antibodies from rabbits immunized with gp195 were measured by using an enzyme-linked immunosorbent assay (ELISA) with purified gpl95s from FUP and FVO as the coating antigens (28). To measure the proportion of the anti-gpl95 antibody response cross-reacting with the heterologous gp195, a competitive inhibition ELISA was performed with parasite-purified FUP and FVO gpl95s.…”

“…In vitro parasite growth inhibition with anti-gp195 sera. Rabbit anti-gpl95 sera were evaluated for their ability to inhibit the growth of homologous and heterologous parasites (FUP or FVO) by using established methods (28). Quarternary day 14 sera were used in inhibition assays.…”

Adjuvant-dependent immune response to malarial transmission-blocking vaccine candidate antigens.

“…This explanation is unlikely, however, because there was no evidence of uncleaved fusion protein by immunoblotting or protein staining (data not shown) . An alternate explanation is that an immunogen of whole gametes contains a mixture of gamete proteins, carbohydrates, lipids, and membrane structures, one or some of which limit the immune MPL, a nontoxic LPS derivative of Gram-negative bacterial endotoxin (21), and trehalose dimycolate, a component of mycobacterial cell walls (22), have been shown to increase antibody response to a variety of antigens, including malarial proteins (23,24). The combination of MPL and TDM is a particularly potent immunological adjuvant (25,26).…”

Immunotherapy Can Enhance Anthelmintic Efficacy in Alveolar Echinococcosis

“…Muramyldipeptide (MDP) is the smallest bacterial structure with immunopotent activity. The positive effect of MDP on the host immune response was also observed in several parasitic infections [25][26][27]. Muramyltripeptide phosphatidylethanolamine (MTP-PE) is a lipofilic derivate of MDP.…”