Abstract:
One approach towards the development of a vaccine against malaria is to immunize against the
parasite sexual stages that mediate transmission of the parasite from man to mosquito. Antibodies
against these stages, ingested with the blood meal, inhibit the parasite development in
the mosquito vector, constituting "transmission blocking immunity." Most epitopes involved
in transmission-blocking immunity depend on the tertiary conformational structure of surface
antigens. However, one of the transmission-blocking monodonal antibodies we have raised against
Plasmodium vivax reacts with a linear epitope on both asexual stages and gametes. This monoclonal
antibody (A12) is capable of totally blocking development of the parasite in the mosquito
host when tested in membrane feeding assays with gametocytes from P. vivax-infected patients.
Immune screening of a P. vivax Xgtll genomic expression library with A12 led to the isolation
of a clone to which was mapped the six-amino acid epitope recognized by A12. Antisera raised
in mice against a 12-mer synthetic peptide containing this epitope coupled to bovine serum albumin
not only had high titers of antipeptide antibodies as measured by enzyme-linked immunosorbent
assay, but in addition recognized the same 24- and 57-kD parasite components
as A12 on Western blots and reacted with the parasite by immunofluorescence. When tested
in membrane feeding assays, these antibodies have significant suppressive effects on parasite development
in the mosquito.
