Extracellular vs. Intracellular Parasitic Mechanisms of Immune Evasion: Leishmania



Figure 1: Phlebotomine sandfly (14)

Leishmania causes the disease Leishmaniasis and primarily affects the populations of developing countries, causing high rates of morbidity and mortality (1). The parasite uses the sandfly as a vector (Figure 1), and is preserved in an alarming number of animal reservoirs including sloths, dogs, opossums, and asymptomatic


There are three clinically distinguishable types of leishmaniasis: cutaneous, mucocutaneous, and visceral (Figure 2):

Figure 2: Clinical presentations of Leishmaniasis

Figure 3: Leishmania life cycle

All three types of leishmaniasis can be caused by a number of Leishmania species. Though the parasite resides exclusively in macrophages and therefore uses several intracellular evasion tactics, it also employs extracellular mechanisms when it is outside of a cell and waiting to be phagocytosed by a macrophage. The timing of the parasite’s humoral and cell-mediated responses can be seen in its life cycle (Figure 3). Because Leishmania utilizes both types of immune system evasion, it is an ideal parasite with which to model overall parasitic immune system evasion (3).


© 2007 The Board of Trustees of the Leland Stanford Junior University. All rights reserved.