Vaccination against cutaneous leishmaniasis in mice using nonpathogenic cloned promastigotes of Leishmania major and importance of route of injection

Abstract

In vaccination studies, mice have been injected by different routes with living promastigotes of nonpathogenic leishmania followed by cutaneous challenge with pathogenic promastigotes. Parasites used for vaccination have been promastigotes of the cloned parasite lines A12 and A52 derived from Leishmania major isolate L137, or long-term cultured promastigotes of the leishmaniasis recidiva isolate, L32 (L.t.tropica). None of these protozoa causes lesions after cutaneous injection to mice. Disease in previously injected mice has been monitored after cutaneous challenge with promastigotes of a virulent cloned line, V121, derived from isolate L137. Mice used were C57BL/6 (genetically resistant), BALB/c and BALB/c.H-2b (genetically susceptible) and BALB/c.H-2k (also genetically susceptible but sometimes less so than BALB/c). C57BL/6 mice were almost completely resistant to subsequent cutaneous disease when challenged after intraperitoneal injection of viable nonpathogenic cloned promastigotes. In contrast, BALB/c, BALB/c.H-2b and BALB/c.H-2k mice challenged after intravenous or intraperitoneal injection were only protected partially against cutaneous leishmaniasis. These vaccinated mice generally showed persistent low grade cutaneous disease for many months after challenge. High doses of viable L32 promastigotes injected intraperitoneally were also able to induce a degree of resistance to subsequent cutaneous leishmaniasis. Using any protocol, subcutaneous injections have been totally without protective effects as have been killed promastigotes injected by any route to mice. Subcutaneous injections appear to be ineffective rather than counterproductive in that mice injected by both the intravenous and subcutaneous routes with nonpathogenic living cloned promastigotes resemble mice injected by the intravenous route in their disease status following challenge.