Evaluation of the optimal inoculation of leishmania major culture-derived stationary phase promastigotes required to assess protective immune status in the vervet monkey model

ABSTRACT

"Vervet monkeys have been shown to be resistant to a homologous challenge of Leishmania major after an active infection followed by self cure responses. Confirmation of the protective immune status of such animals was demonstrated by exposing a group of 4 monkeys to multiple infected sandfly challenge. Two animals revealed small transient nodule formation while in the remaining two; no signs or symptoms were obvserved. In order to ascertain the level of promastigote challenge which was equivalent to such a ""natural"" fly challenge; 3 additional groups of immune vervet monkeys were challenged with 1x103; 1x104 and 105 stationary phase culture promastigotes in the presence of salivary gl and lysates. In all groups; there was no lesion development whatsoever. A second challenge of 1x106; 1x107 and 4x107 in these same animal groups; revealed self healing nodules in the group inoculated with 1x106 promastigotes whilst in the remaining 2 groups challeged at the higher levels; there was nodule formation which progressed to ulceration. A challenge dose of 1x105 culture promastigotes was thus considered to be optimal since this level of challenge in naive animals was demonstrated to result in ulcer formation when inoculated with salivary gland lysates."