Brugia malayi: comparison of protective immune responses induced by Bm-alt-2 DNA, recombinant Bm-ALT-2 protein and prime-boost vaccine regimens in a jird model

Abstract

Immunization of jirds with Bm-alt-2 elicited partial protection against challenge infection with the filarial parasite Brugia malayi. In this study, we initially compared the protective immune responses elicited following immunization with recombinant Bm-ALT-2 protein regimen and Bm-alt-2 DNA regimen. These studies showed that protein vaccination conferred approximately 75% protection compared to DNA vaccination that conferred only 57% protection. Analysis of the protective immune responses showed that the protein immunization promoted a Th2-biased response with an increase in IL-4, IL-5 and IgG1 responses, whereas, the DNA vaccine promoted a Th1-biased response with profound IFN-gamma and IgG2a responses. Since protein vaccination gave better results than DNA vaccination, we then wanted to evaluate whether a prime-boost vaccination that combined DNA prime and protein boost will significantly increase the protective responses induced by the protein vaccine. Our results suggest that prime-boost vaccination had no added advantage and was comparatively less effective (64% protection) than the Bm-ALT-2 protein alone vaccination. Prime boost vaccination generated mixed Th1/Th2 responses with a slightly diminished Th2 responses compared to protein vaccination. Thus, our results suggest that Bm-ALT-2 protein vaccination regimen may be slightly better than prime-boost vaccine regimen and the mechanism of protection appears to be largely mediated by a Th2-biased response.

Fig. 1

Schematic representation of the immunization protocol used in this study.

Fig. 2

Bm-ALT-2 specific IgG titer in jirds immunized by different protocols. Jirds were bled 15 days after the last immunization and Bm-ALT-2-specific IgG titer was detected by ELISA. Optical density was measured at 405 nm. Antibody titer is defined as reciprocal dilution of the sera yielding a one-half maximal absorbance at 405 nm. Data represent mean titers (in logarithmic scale) and standard errors for each group of animals.

Fig. 3

Ratio of IgG1 titer to IgG2a titer in different groups. The ratio of IgG1/IgG2a was obtained by dividing the titer of IgG1 by that of IgG2a. Data presented are means (in boxes) and SD values.

Fig. 4

Lymphocyte proliferative responses to Bm-ALT-2. Spleen cells were collected from immunized animals and stimulated with Bm-ALT-2. Data shown are means ± standard deviations of stimulation index.

Fig. 5

Cytokine mRNA levels. Spleen cells were stimulated with 10 μg/ml of Bm-ALT-2 protein for 72 h. Cytokine mRNA expression was analyzed by RT-PCR. The actual densitometric values for each cytokine mRNA were normalized by using β-actin densitometry as the 100% reference, and all other values are expressed as percentages of β-actin.