Antigenic variation in Leishmania mexicana following infection of immunized mice leads to relative sparing of suppressor determinants.

Intravenous immunization of BALB/c mice with irradiated Leishmania mexicana slows the growth of a subsequent intradermal inoculation of virulent parasites. Prior subcutaneous immunization with irradiated parasites before i.v. immunization blocks the protective effect of the latter. Parasites harvested from vaccinated mice grow more slowly in naive mice than the initial inoculated clone, and have a diminished capacity to immunize mice against this initial clone when used as (irradiated) i.v. immunogen. However, parasites harvested from vaccinated mice are as effective as the initial clone in blocking protection when used as subcutaneous immunogen. Understanding the nature of this differential response in expression of protecting/suppressor determinants in parasites harvested from vaccinated or naive mice will likely be important to developing a suitable vaccination strategy for human use.