Differences in human macrophage receptor usage, lysosomal fusion kinetics and survival between logarithmic and metacyclicLeishmania infantum chagasipromastigotes

Abstract

SummaryThe obligate intracellular protozoan, Leishmania infantum chagasi (Lic) undergoes receptormediated phagocytosis by macrophages followed by a transient delay in phagolysosome maturation. We found differences in the pathway through which virulent Lic metacyclic promastigotes or avirulent logarithmic promastigotes are phagocytosed by human monocyte-derived macrophages (MDMs). Both logarithmic and metacyclic promastigotes entered MDMs through a compartment lined by the third complement receptor (CR3). In contrast, many logarithmic promastigotes entered through vacuoles lined by mannose receptors (MR) whereas most metacyclic promastigotes did not (P < 0.005). CR3-positive vacuoles containing metacyclic promastigotes stained for caveolin-1 protein, suggesting CR3 localizes in caveolae during phagocytosis. Following entry, the kinetics of phagolysosomal maturation and intracellular survival also differed. Vacuoles containing metacyclic parasites did not accumulate lysosomeassociated membrane protein-1 (LAMP-1) at early times after phagocytosis, whereas vacuoles with logarithmic promastigotes did. MDMs phagocytosed greater numbers of logarithmic than metacyclic promastigotes, yet metacyclics ultimately replicated intracellularly with greater efficiency. These data suggest that virulent metacyclic Leishmania promastigotes fail to ligate macrophage MR, and enter through a path that ultimately enhances intracellular survival. The relatively quiescent entry of virulent Leishmania spp. into macrophages may be accounted for by the ability of metacyclic promastigotes to selectively bypass deleterious entry pathways.

Attenuation of Leishmania infantum chagasi Metacyclic Promastigotes by Sterol Depletion

“…Furthermore, a decreased abundance of ligand for the macrophage CR3 receptor (iC3b) on the promastigote surface would likely decrease the proportion of promastigotes ligating that receptor and possibly direct parasites to enter through different phagocytic receptors such as the mannose receptor. Phagocytosis through alternate receptors can alter the kinetics and efficiency of uptake and affect the ultimate survival of intracellular parasites, as illustrated in our recent report comparing avirulent to virulent parasite entry into macrophages (38). Similar to those in the prior study, our current observations may provide another example in which enhanced macrophage entry does not translate into enhanced intracellular survival (38).…”

“…One plausible explanation is that M␤CD-treated cells bind to alternate macrophage receptors via ligands exposed by sterol depletion or via the enhanced opsonic C3, such as CR1 or mannose receptor (55). A parallel observation is made in the case of L. infantum chagasi logarithmic-phase promastigotes, which contain only one-fourteenth the level of steady-state MSPs of stationary-phase promastigotes (13) but contain only one-third of the MSPs of metacyclic promastigotes (18), yet their phagocytosis by MDMs is more efficient than that of metacyclic promastigotes (38).…”

“…Phagocytosis through alternate receptors can alter the kinetics and efficiency of uptake and affect the ultimate survival of intracellular parasites, as illustrated in our recent report comparing avirulent to virulent parasite entry into macrophages (38). Similar to those in the prior study, our current observations may provide another example in which enhanced macrophage entry does not translate into enhanced intracellular survival (38). We hypothesize that the decreased abundance of MSP, a protease that cleaves C3b to iC3b, results in a greater proportion of C3b on treated parasites (12).…”

“…Serum-opsonized Leishmania promastigotes have been found to ligate two complement receptors on the surface of macrophages: CR3, which binds the inactive C3b derivative iC3b, and CR1, which binds C3b but also has a low affinity for iC3b (35)(36)(37). Phagocytosis stimulated through ligation of different receptors can lead to different rates or pathways of intracellular trafficking and consequent parasite survival (38). As such, if sterol content affects the type or amount of complement opsonization, this could influence parasite entry and survival.…”

Transmission and Epidemiology of Zoonotic Protozoal Diseases of Companion Animals

“…Leishmania phagocytosis is mediated through complement receptors 1 and 3 and mannose scavenger receptors, indicating both opsonization-dependent and -independent mechanisms of invasion (300). Uptake results in the reorganization of F-actin and delayed phagolysosomal fusion (300,301). Leishmania spp.…”