No. 21 (10 Nov. 2006): 1-15
Accepted: 25 Sept. 2006
Potential role of lectins in ticks:
Rhipicephalus
appendiculatus and Rhipicephalus
pulchellus (Acari: Ixodidae)
ESTHER KIBUKA-SEBITOSI
Centre for African Renaissance
Studies (CARS), University of South Africa (UNISA) 287 Skinner Street,
Pretoria, P.O. Box 392,
UNISA, 0003 Pretoria, South Africa; E-mail: sebitek@unisa.ac.za
Abstract
The role of lectins in
tick vectors was investigated by comparing the presence of lectins in the
hemolymph, guts and salivary
glands of two tick species: (1) Rhipicephalus appendiculatus, the
vector of Theileria parva, and (2) Rhipicephalus
pulchellus, which is
refractory to this protozoan parasite. There was variation in the
agglutination titres with
erythrocytes from bovine, mouse and rabbit erythrocytes, suggesting different
binding affinities and quantities
of lectins. The hemolymph from R. pulchellus gave the highest
agglutination titer with mouse erythrocytes
(1024) compared to that obtained with rabbit cells (8). No agglutination was
observed with bovine erythrocytes
when assayed with the gut, salivary gland or hemolymph lectins from either
tick species. The gut lectin from
R. pulchellus also demonstrated high titers (1024) with rabbit cells
but moderate titers with mouse erythrocytes
(256). Hemolymph from T. parva- infected R. appendiculatus contained
double (512) the quantities of
lectins compared to uninfected ticks (256) with mouse erythrocytes suggesting
an increase in the amount of
lectin in the presence of infection and implying a role of lectins in the
immunity of these arthropods. Lectin
from the gut of R. appendiculatus agglutinated purified piroplasms, a
stage in the T. parva life cycle ingested
by the tick when it feeds on infected cattle. The anti-lectin antibodies
conjugated with Fluorescein isothiocyanate
(FITC) bound to the piroplasms, suggesting a possible point at which
intervention may be developed for
the control of theileriosis. The significance of lectins in tick parasite
transmission lies in the fact that
these molecules play an important part in cell-to-cell adhesion. Defining
their binding specificities and quantities
in a given tick species may lead to development of a novel type of disease
control whose mode of action
would be based on competing for the ligands for binding to pathogen receptors
or preventing adhesion to host
tissues (transmission-blocking), thereby preventing infection.
This study revealed that
tick-derived antigens in the form of lectins produced antibodies that
recognized the piroplasm as well
as schizont stages of T. parva. With increasing attention on
vaccination of cattle against ticks,
there is a need to identify and show target antigens within the tick. The
study has elucidated three targets, the
salivary gland, hemolymph and the gut. It forms one of the first reports on
the effect of lectin antibody on the
development and transmission of T. parva. This also means that lectins
may be used as disease immunogens that
can possibly intervene at the piroplasm stage and the schizont stage.
Key words: Lectins,
ticks, Transmission blocking vaccine, Rhipicephalus
appendiculatus, Rhipicephalus pulchellus
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