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. 2009 Feb 27;8:35.
doi: 10.1186/1475-2875-8-35.

AFCo1, a Meningococcal B-derived Cochleate Adjuvant, Strongly Enhances Antibody and T-cell Immunity Against Plasmodium Falciparum Merozoite Surface Protein 4 and 5

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AFCo1, a Meningococcal B-derived Cochleate Adjuvant, Strongly Enhances Antibody and T-cell Immunity Against Plasmodium Falciparum Merozoite Surface Protein 4 and 5

Gustavo Bracho et al. Malar J. .
Free PMC article

Abstract

Background: Whilst a large number of malaria antigens are being tested as candidate malaria vaccines, a major barrier to the development of an effective vaccine is the lack of a suitable human adjuvant capable of inducing a strong and long lasting immune response. In this study, the ability of AFCo1, a potent T and B cell adjuvant based on cochleate structures derived from meningococcal B outer membrane proteoliposomes (MBOMP), to boost the immune response against two Plasmodium falciparum antigens, merozoite surface protein 4 (MSP4) and 5 (MSP5), was evaluated.

Methods: Complete Freund's adjuvant (CFA), which is able to confer protection against malaria in animal MSP4/5 vaccine challenge models, was used as positive control adjuvant. MSP4 and 5-specific IgG, delayed-type hypersensitivity (DTH), T-cell proliferation, and cytokine production were evaluated in parallel in mice immunized three times intramuscularly with MSP4 or MSP5 incorporated into AFCo1, synthetic cochleate structures, CFA or phosphate buffered saline.

Results: AFCo1 significantly enhanced the IgG and T-cell response against MSP4 and MSP5, with a potency equivalent to CFA, with the response being characterized by both IgG1 and IgG2a isotypes, increased interferon gamma production and a strong DTH response, consistent with the ability of AFCo1 to induce Th1-like immune responses.

Conclusion: Given the proven safety of MBOMP, which is already in use in a licensed human vaccine, AFCo1 could assist the development of human malaria vaccines that require a potent and safe adjuvant.

Figures

Figure 1
Figure 1
Influence of adjuvant on anti-MSP4 and MSP5 IgG production. The adjuvant effect of AFCo1, SCS or CFA on the immune response against MSP4 or MSP5 was explored in separated immunization experiments. Mice were injected with three intramuscular doses at a 14-day interval of MSP4 or MSP5 incorporated into AFCo1 or SCS, or mixed with CFA or PBS. Serum samples were taken 21 days after the last immunization, MSP4 (Panel A) or MSP5 (Panel B)-specific IgG were measured by ELISA. Antibodies levels are expressed as a logarithm of the titer. Each experiment was repeated 3 times. The means and standard deviations are showed. * Significant differences by Tukey test (p < 0.05) compared with PBS group.
Figure 2
Figure 2
Influence of adjuvant on anti-MSP4 and MSP5 IgG isotype production. The adjuvant effect of AFCo1, SCS, CFA or PBS on the immune response against MSP4 or MSP5 was compared. Mice were injected with three intramuscular doses at a 14 day interval of MSP4 or MSP5 incorporated into AFCo1 or SCS, or mixed with CFA or PBS. MSP-specific IgG1 and IgG2a were measured by ELISA in serum taken 21 days after the last immunization. (Panel A) MSP4-specific IgG1 (open bars) and IgG2a (lined bars) from MSP4 immunized mice. (Panel B) MSP5-specific IgG1 (filled bars) and IgG2a (lined bars) from MSP5 immunized mice. Antibodies levels are expressed as a logarithm of the titer. The means and standard deviations of 3 different experiments are shown. * Significant differences by Tukey test (p < 0.05).).
Figure 3
Figure 3
Delayed type hypersensitivity reaction induced by intradermal challenge with MSP4 or MSP5 in immunized mice. Mice were immunized with MSP4 or MSP5 incorporated into AFCo1 or SCS, or mixed with CFA or PBS (3 intramuscular doses, 14 day interval). The presence of delayed type hypersensitivity (DTH) was tested 21 days after the last immunization by intradermal challenge with 5 μg of MSP4 or MSP5 in the left footpad. PBS was injected in the right footpad as control. The size of inflammation in both footpaths was measured 48 h after challenge using a caliper. The induration induced by the antigen was measured as the difference of right minus left footpad thickness. The magnitude of DTH reaction induced by MSP4 (Panel A) and MSP5 (Panel B) immunization are expressed as the mean and standard deviation of the induration in each experimental group. * Significant differences by Tukey test (p < 0.05).
Figure 4
Figure 4
Influence of adjuvant on MSP4 or MSP5-induced splenocyte proliferation. Splenocytes from mice immunized with MSP4 or MSP5 in different adjuvants were isolated, stained with CFSE and cultured in the presence of MSP4 or MSP5 at 10 μg/ml. HBsAg was used as an unrelated antigen control. PHA and medium alone were used as positive and negative controls respectively (data not show). After 5 days, proliferation was detected by the presence of cells with a decreased fluorescence intensity compared with the negative control (medium control). The frequencies of MSP4 (Panel A) or MSP5 (Panel B) specific proliferating cells are expressed as percentages of the total population. Proliferating populations were identified and quantified by gating specific proliferating cells previously stained with anti-CD4, CD8 or CD19 PE labeled monoclonal antibodies. The distribution of proliferating populations is showed as percentages of the total number of MSP4 (Panel C) or MSP5 (Panel D) stimulated proliferating cells.
Figure 5
Figure 5
Influence of adjuvant on MSP4 or MSP5-induced cytokine production. Splenocytes from mice immunized with MSP4 or MSP5 in different adjuvants were cultured in the presence of MSP4 or MSP5 at 10 μg/ml. After 5 days of culture, supernatants were colleted and analysed for the presence of IFNγ or IL5 using a capture sandwich ELISA. Panel A shows the levels of IFNγ and IL5 produced by spleen cells from mice immunized with MSP4 in AFCo1, SCS, PBS or CFA after in vitro recall with MSP4; whereas panel B shows the levels of IFNγ and IL5 produced by spleen cells from mice immunized with MSP5 in AFCo1, SCS, PBS or CFA after in vitro recall with MSP5. The means and standard errors are shown. * Significant differences by Tukey test (p < 0.05).

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