Naturally occurring agglutinins against trypanosomatid flagellates in the haemolymph of insects

In vitro studies of the behaviour of the trypanosomatid flagellates Trypanosoma brucei and Leishmania hertigi in the presence of cell-free haemolymph of locusts, Schislocerca gregaria and cockroaches, Periplaneta americana revealed the presence of parasite agglutinins. The range of normal values of agglutination titres was 2-4to 2–13. Physicochemical treatment of haemolymph indicated that these agglutinins are protein or glycoprotein in nature and are only partially affected by heat treatment below 65 °C, at which temperature incubation of haemolymph for 30 min abrogated all agglutination. Agglutination was not dependent on the presence of Ca2+or Mg2+. Prior injection of locusts and cockroaches with T. brucei and L. hertigi significantly increased agglutinin titres between Days 4 and 6 in cockroaches (P < 0. 05) and from Days 2 to 4 when L. hertigi was inoculated into locusts. The induced differences in titres observed in locusts infected with T. brucei were not significant. Lysozyme levels were significantly increased after inoculation of T. brucei into cockroaches compared with placebo-inoculated and uninoculated controls. L. hertigi inoculation produced significant increases in lysozyme levels compared with controls between Days 1 and 7 in locusts and 3 to 6 in cockroaches. These studies indicate that, at least in easily manipulated model systems, induced responses to intrahaemocoelic inoculation to trypanosomes and Leishmania can occur. As far as we are aware this is the first report of an induced response of an insect to such important parasites. The possibility that induced responses in natural vectors to these parasites occurs requires investigation.