The Abundant Larval Transcript-1 and -2 Genes ofBrugia malayiEncode Stage-Specific Candidate Vaccine Antigens for Filariasis

Abstract

Lymphatic filariasis is a major tropical disease caused by the mosquito-borne nematodes Brugia and Wuchereria. About 120 million people are infected and at risk of lymphatic pathology such as acute lymphangitis and elephantiasis. Vaccines against filariasis must generate immunity to the infective mosquito-derived third-stage larva (L3) without accentuating immunopathogenic responses to lymphatic-dwelling adult parasites. We have identified two highly expressed genes, designated abundant larval transcript-1 and -2 (alt-1 and alt-2), from each of which mRNAs account for >1% of L3 cDNAs. ALT-1 and ALT-2 share 79% amino acid identity across 125 residues, including a putative signal sequence and a prominent acidic tract. Expression of alt-1 and alt-2 is initiated midway through development in the mosquito, peaking in the infective larva and declining sharply following entry into the host. Humans exposed to Brugia malayi show a high frequency of immunoglobulin G1 (IgG1) and IgG3 antibodies to ALT-1 and -2, distinguishing them from adult-stage antigens, which are targeted by the IgG4 isotype. Immunization of susceptible rodents (jirds) with ALT-1 elicited a 76% reduction in parasite survival, the highest reported for a single antigen from any filarial parasite. ALT-1 and the closely related ALT-2 are therefore strong candidates for a future vaccine against human filariasis.Filarial nematodes are helminth parasites which are responsible for lymphatic filariasis, a tropical disease afflicting some 119 million people (26,28,34). The parasites have a complex life cycle in which mosquito-borne infective third-stage larvae (L3) invade the human body, mature to adult worms, and produce large numbers of newborn larvae (microfilariae) which must transit the mosquito vector in order to develop to L3 (16). Overt disease has a major immunopathologic component, and a prominent risk of vaccination with filarial antigens is exacerbation of pathology (22,27,32). The target of immunopathological reactions, however, is thought to be the longlived adult worm and not the infective larva (23,29).To date, strategies to identify vaccine antigens in filariasis have relied on serum antibodies to define antigens, whether by comparing apparently uninfected subjects with infected patients (11) or by using sera from animals vaccinated with radiation-attenuated parasites (19,20). Among the antigens so discovered have been several with high levels of similarity to host antigens (such as muscle proteins), raising an additional specter of autoimmune induction by vaccination. No recombinant filarial antigen yet tested induces significant degrees of immunity to challenge infection (21, 30), indicating that an alternative criterion needs to be adopted.We describe here a molecular biological approach, the analysis of mRNAs which are highly and selectively expressed by the mosquito-derived larva at the time that it is competent to infect the mammalian host. We sought to identify new antigens which are restricted to this stage and absent from the mature for...

Stage-specific proteomic expression patterns of the human filarial parasiteBrugia malayiand its endosymbiontWolbachia

“…Some of these immunologically relevant proteins have been described previously (23-33) and relate to those molecules that are highly immunogenic in human infections or that have activity on the mammalian host immune response (through mimicry or other mechanisms). These data corroborate a number of previous studies that demonstrate stage-specific expression and/or serologic reactivity of ALT-2 and the larval allergens (in the L3 stage) (34) and BmR1 (35), BmMIF (36), TGF-β homologue (30), SXP-1 (37), galectins (38), and microfilarial sheath proteins (in the microfilarial stage) (39). Particular sets of ECM-associated proteins were common and highly enriched in the both the L3s (SI Appendix, Fig.…”

The Larval Specific Lymphatic Filarial ALT‐2: Induction of Protection Using Protein or DNA Vaccination

“…These findings are in accordance with findings observed among subjects in a brugian filariasis endemic area, where recognition of the recombinant ALT-1 protein was predominantly by IgG3 and IgG1 but not by IgG4 (16,25). The greater response among patients with chronic pathology compared to the microfilaremics may be due to the presence of concomitant immunity, a phenomenon broadly characteristic of helminthic infections, where the presence of an active infection induces an immune response against the incoming infective larvae leading to resistance (9,10,35).…”

“…The protective efficacy we observed with B. malayi ALT-2 in the mouse micropore chamber model of 74.24% reduction in viable larval recovery is similar to the 76% reduction in parasite survival following immunization with the recombinant Brugia malayi ALT-1 protein reported earlier by Gregory et al (16). The level of reduction in parasite survival on immunization with the larval stage antigen of the ALT gene family is the highest level of protection reported so far for an individual antigen (16).…”

“…Comparison of the bancroftian and brugian ALT-2 revealed that both possess an N-terminal signal leader peptide followed by an acidic tract and basic C-termini, an arrangement similar to that of other alt genes described (16) Because of the lack of availability of animal models for W. bancrofti and the significant homology shared between the W. bancrofti and B. malayi ALT-2 genes, we chose to study the prophylactic potential of the B. malayi ALT-2 in further studies.…”

“…One group of such transcripts, termed Abundant Larval Transcripts (ALT-1, ALT-2 and ALT-3) were found to share significant sequence homology to the Dirofilaria immitis 20/22 kDa developmentally regulated excretory/secretory protein, itself a vaccine candidate. Subjects from a Brugia malayi-endemic area were demonstrated to have an antibody response to recombinant ALT-1, and the recombinant protein was also observed to induce 76% protection in a jird model of protective immunity (16).…”