The adjuvant-free immunoprotection of recombinant filarial protein Abundant Larval Transcript-2 (ALT-2) in Mastomys coucha and the immunoprophylactic importance of its putative signal sequence

The filarial protein Abundant Larval Transcript-2 (ALT-2) of the filarial parasite Brugia malayi has been shown to produce 74% worm clearance when administered with an adjuvant. In the present study, we show that it not only induces humoral and cell-mediated immunity, but also protection up to 71% in Mastomys coucha, a permissive animal model for filariasis, even without adjuvant. This unique feature of ALT-2 protein is highly restricted to its 21 amino acid N-terminal signal sequence, the absence of which resulted in poor immune response as well as immunoprotection (49%). Moreover, ALT-2 is likely to exert immunoprotection effects in B. malayi infection by maintaining a Th1-Th2 balance, evident from higher levels of IgG1 and IgG2a as well as IL-4 and IFN-γ. An improved understanding about the role of this filarial protein in host immunity, host-parasite interaction and worm clearance will aid in the development of good immunoprophylaxis for the disease.

Highlights► Brugia malayi ALT-2 produces 71% worm clearance in Mastomys coucha even without adjuvant. ► Adjuvant-free immunoprotection of ALT-2 restricted to its 21 amino acid putative signal sequence. ► The absence of signal sequence resulted in poor immunoprotection (49%). ► ALT-2 maintains Th1-Th2 balance, evident from high levels of IgG1 and IgG2a as well as IL-4 and IFN-γ. ► ALT-2 can enhance the immune response of another third party antigen in the absence of adjuvant.