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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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Related in: MedlinePlus

Promastigote binding to human blood cell populations.  111In-labeled L. donovani promastigotes (5 × 105 cells) were incubated at  37°C for 1 min with 100 μl of (A) heparinized blood; (B) blood supplemented with 10 mM EDTA; and (C) PBS. After incubation, the samples  were centrifuged (500 g, 3 min, 20°C) through a discontinuous Percoll  gradient. Three fractions (1–3), one each from the buffer-Percoll interface  (1); the 63–72% Percoll interface (2); and from the erythrocyte pellet (3)  were collected, processed as described in Materials and Methods, and the  percentage of [111In] cpm in each fraction determined. Data are the mean  values of duplicate samples from a representative experiment of seven  performed.
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Figure 1: Promastigote binding to human blood cell populations. 111In-labeled L. donovani promastigotes (5 × 105 cells) were incubated at 37°C for 1 min with 100 μl of (A) heparinized blood; (B) blood supplemented with 10 mM EDTA; and (C) PBS. After incubation, the samples were centrifuged (500 g, 3 min, 20°C) through a discontinuous Percoll gradient. Three fractions (1–3), one each from the buffer-Percoll interface (1); the 63–72% Percoll interface (2); and from the erythrocyte pellet (3) were collected, processed as described in Materials and Methods, and the percentage of [111In] cpm in each fraction determined. Data are the mean values of duplicate samples from a representative experiment of seven performed.

Mentions: To mimic natural infection conditions, fresh human blood from different donors was infected with 111In-labeled L. donovani promastigotes and the blood–parasite mixture centrifuged through a discontinuous Percoll density gradient to separate cell populations and determine 111In-labeled promastigote distribution (Fig. 1). 1 min after promastigote addition, nearly 100% of the parasites cosedimented with the erythrocyte pellet. In contrast, promastigotes added to EDTA-treated blood or mixed with PBS alone were located at the Percoll-buffer interface after centrifugation. Promastigote cosedimentation with erythrocytes was specific, unrelated to the erythrocyte blood group, and dependent on the presence of serum factors and divalent ions in the reaction mixture. These data show that the parasites bind by IA to erythrocytes immediately after contact with host blood.


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

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

Promastigote binding to human blood cell populations.  111In-labeled L. donovani promastigotes (5 × 105 cells) were incubated at  37°C for 1 min with 100 μl of (A) heparinized blood; (B) blood supplemented with 10 mM EDTA; and (C) PBS. After incubation, the samples  were centrifuged (500 g, 3 min, 20°C) through a discontinuous Percoll  gradient. Three fractions (1–3), one each from the buffer-Percoll interface  (1); the 63–72% Percoll interface (2); and from the erythrocyte pellet (3)  were collected, processed as described in Materials and Methods, and the  percentage of [111In] cpm in each fraction determined. Data are the mean  values of duplicate samples from a representative experiment of seven  performed.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1887685&req=5

Figure 1: Promastigote binding to human blood cell populations. 111In-labeled L. donovani promastigotes (5 × 105 cells) were incubated at 37°C for 1 min with 100 μl of (A) heparinized blood; (B) blood supplemented with 10 mM EDTA; and (C) PBS. After incubation, the samples were centrifuged (500 g, 3 min, 20°C) through a discontinuous Percoll gradient. Three fractions (1–3), one each from the buffer-Percoll interface (1); the 63–72% Percoll interface (2); and from the erythrocyte pellet (3) were collected, processed as described in Materials and Methods, and the percentage of [111In] cpm in each fraction determined. Data are the mean values of duplicate samples from a representative experiment of seven performed.
Mentions: To mimic natural infection conditions, fresh human blood from different donors was infected with 111In-labeled L. donovani promastigotes and the blood–parasite mixture centrifuged through a discontinuous Percoll density gradient to separate cell populations and determine 111In-labeled promastigote distribution (Fig. 1). 1 min after promastigote addition, nearly 100% of the parasites cosedimented with the erythrocyte pellet. In contrast, promastigotes added to EDTA-treated blood or mixed with PBS alone were located at the Percoll-buffer interface after centrifugation. Promastigote cosedimentation with erythrocytes was specific, unrelated to the erythrocyte blood group, and dependent on the presence of serum factors and divalent ions in the reaction mixture. These data show that the parasites bind by IA to erythrocytes immediately after contact with host blood.

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