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Immune adherence-mediated opsonophagocytosis: the mechanism of Leishmania infection.

Domínguez M, Toraño A - J. Exp. Med. (1999)

Bottom Line: We propose that adaptation to the immune adherence mechanism aids Leishmania survival, promoting rapid promastigote phagocytosis by leukocytes.This facilitates host colonization and may represent the parasite's earliest survival strategy.In light of this mechanism, it is unlikely that infection-blocking vaccines can be developed.

View Article: PubMed Central - PubMed

Affiliation: Servicio de Inmunología, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, E-28220 Madrid, Spain.

ABSTRACT
To mimic the sandfly pool feeding process and characterize the cellular and biochemical events that occur during the early stages of promastigote-host interaction, we developed an ex vivo model of human blood infection with Leishmania promastigotes. Within 30 s of blood contact, Leishmania promastigotes bind natural anti-Leishmania antibodies, which then activate the classical complement pathway and opsonization by the third component of complement. The opsonized promastigotes undergo an immune adherence reaction and bind quantitatively to erythrocyte CR1 receptors; opsonized Leishmania amastigotes also bind to erythrocytes. Progression of infection implies promastigote transfer from erythrocytes to acceptor blood leukocytes. After 10 min of ex vivo infection, 25% of all leukocytes contain intracellular parasites, indicating that blood cells are the early targets for the invading promastigotes. We propose that adaptation to the immune adherence mechanism aids Leishmania survival, promoting rapid promastigote phagocytosis by leukocytes. This facilitates host colonization and may represent the parasite's earliest survival strategy. In light of this mechanism, it is unlikely that infection-blocking vaccines can be developed.

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Kinetic and promastigote viability course of the IA  reaction. 111In-labeled L. donovani promastigotes (5 × 105 cells)  were mixed with 100 μl of heparinized blood and incubated at  37°C for 0, 10, 20, 30, 60, 120,  and 240 s. After incubation, the  samples were centrifuged (500 g,  3 min, 20°C) through 72% Percoll. The Percoll solution (free  parasites) and the erythrocyte pellet (erythrocyte-bound parasites)  were collected separately, filtered,  and the percentage of [111In] cpm  retained was determined. Promastigote viability (▴) and erythrocyte-bound promastigote (•)  profiles were calculated as described in Materials and Methods.  Data are the mean value of duplicate samples from a representative  experiment of three similar experiments performed.
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Figure 2: Kinetic and promastigote viability course of the IA reaction. 111In-labeled L. donovani promastigotes (5 × 105 cells) were mixed with 100 μl of heparinized blood and incubated at 37°C for 0, 10, 20, 30, 60, 120, and 240 s. After incubation, the samples were centrifuged (500 g, 3 min, 20°C) through 72% Percoll. The Percoll solution (free parasites) and the erythrocyte pellet (erythrocyte-bound parasites) were collected separately, filtered, and the percentage of [111In] cpm retained was determined. Promastigote viability (▴) and erythrocyte-bound promastigote (•) profiles were calculated as described in Materials and Methods. Data are the mean value of duplicate samples from a representative experiment of three similar experiments performed.

Mentions: The kinetics are shown of erythrocyte–promastigote (E-P) interaction and the promastigote viability profile over a 4-min ex vivo infection period (Fig. 2). Within the first 30 s, the IA reaction has reached completion, and the promastigote inoculum binds completely to erythrocytes. To calculate the on-rate constant (k+1) of this reaction, it is assumed that the E-P interaction occurs between cell particles (1,000:1 to 500:1 ratio) rather than between erythrocyte CR1 receptors and promastigote-bound C3b ligands. In the incubation mixture [E] >> [P], and the interaction is treated as a pseudo-first order process, giving a k+1 value of 3 × 1010 mol−1 s−1. Provided that promastigote-associated [111In] cpm parallels parasite viability, >90% of all viable promastigotes remain erythrocyte-bound during the incubation period. Promastigote viability was high during the first 60 s of incubation; between 60 and 120 s, a sharp decrease in the initial erythrocyte-bound [111In] cpm was observed due to complement lysis. A similar promastigote lysis course is obtained by incubating 111In-labeled promastigotes in the presence of 25% NHS; under these conditions, the 111In-labeled promastigote half-life measured was ∼90 s, by which time promastigote flagellar mobility was already impaired (data not shown).


Immune adherence-mediated opsonophagocytosis: the mechanism of Leishmania infection.

Domínguez M, Toraño A - J. Exp. Med. (1999)

Kinetic and promastigote viability course of the IA  reaction. 111In-labeled L. donovani promastigotes (5 × 105 cells)  were mixed with 100 μl of heparinized blood and incubated at  37°C for 0, 10, 20, 30, 60, 120,  and 240 s. After incubation, the  samples were centrifuged (500 g,  3 min, 20°C) through 72% Percoll. The Percoll solution (free  parasites) and the erythrocyte pellet (erythrocyte-bound parasites)  were collected separately, filtered,  and the percentage of [111In] cpm  retained was determined. Promastigote viability (▴) and erythrocyte-bound promastigote (•)  profiles were calculated as described in Materials and Methods.  Data are the mean value of duplicate samples from a representative  experiment of three similar experiments performed.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC1887685&req=5

Figure 2: Kinetic and promastigote viability course of the IA reaction. 111In-labeled L. donovani promastigotes (5 × 105 cells) were mixed with 100 μl of heparinized blood and incubated at 37°C for 0, 10, 20, 30, 60, 120, and 240 s. After incubation, the samples were centrifuged (500 g, 3 min, 20°C) through 72% Percoll. The Percoll solution (free parasites) and the erythrocyte pellet (erythrocyte-bound parasites) were collected separately, filtered, and the percentage of [111In] cpm retained was determined. Promastigote viability (▴) and erythrocyte-bound promastigote (•) profiles were calculated as described in Materials and Methods. Data are the mean value of duplicate samples from a representative experiment of three similar experiments performed.
Mentions: The kinetics are shown of erythrocyte–promastigote (E-P) interaction and the promastigote viability profile over a 4-min ex vivo infection period (Fig. 2). Within the first 30 s, the IA reaction has reached completion, and the promastigote inoculum binds completely to erythrocytes. To calculate the on-rate constant (k+1) of this reaction, it is assumed that the E-P interaction occurs between cell particles (1,000:1 to 500:1 ratio) rather than between erythrocyte CR1 receptors and promastigote-bound C3b ligands. In the incubation mixture [E] >> [P], and the interaction is treated as a pseudo-first order process, giving a k+1 value of 3 × 1010 mol−1 s−1. Provided that promastigote-associated [111In] cpm parallels parasite viability, >90% of all viable promastigotes remain erythrocyte-bound during the incubation period. Promastigote viability was high during the first 60 s of incubation; between 60 and 120 s, a sharp decrease in the initial erythrocyte-bound [111In] cpm was observed due to complement lysis. A similar promastigote lysis course is obtained by incubating 111In-labeled promastigotes in the presence of 25% NHS; under these conditions, the 111In-labeled promastigote half-life measured was ∼90 s, by which time promastigote flagellar mobility was already impaired (data not shown).

Bottom Line: We propose that adaptation to the immune adherence mechanism aids Leishmania survival, promoting rapid promastigote phagocytosis by leukocytes.This facilitates host colonization and may represent the parasite's earliest survival strategy.In light of this mechanism, it is unlikely that infection-blocking vaccines can be developed.

View Article: PubMed Central - PubMed

Affiliation: Servicio de Inmunología, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, E-28220 Madrid, Spain.

ABSTRACT
To mimic the sandfly pool feeding process and characterize the cellular and biochemical events that occur during the early stages of promastigote-host interaction, we developed an ex vivo model of human blood infection with Leishmania promastigotes. Within 30 s of blood contact, Leishmania promastigotes bind natural anti-Leishmania antibodies, which then activate the classical complement pathway and opsonization by the third component of complement. The opsonized promastigotes undergo an immune adherence reaction and bind quantitatively to erythrocyte CR1 receptors; opsonized Leishmania amastigotes also bind to erythrocytes. Progression of infection implies promastigote transfer from erythrocytes to acceptor blood leukocytes. After 10 min of ex vivo infection, 25% of all leukocytes contain intracellular parasites, indicating that blood cells are the early targets for the invading promastigotes. We propose that adaptation to the immune adherence mechanism aids Leishmania survival, promoting rapid promastigote phagocytosis by leukocytes. This facilitates host colonization and may represent the parasite's earliest survival strategy. In light of this mechanism, it is unlikely that infection-blocking vaccines can be developed.

Show MeSH
Related in: MedlinePlus