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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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Amastigote IA. (A) AO-stained amastigote rosettes with human erythrocytes. Rosettes were formed as described in Materials and Methods.  After incubation, samples were stained and photographed (×790). (B) Amastigote IA reaction. 50-μl aliquots each of a 10% washed erythrocyte suspension, L. amazonensis amastigotes (2 × 107 cells/ml), and 33% NHS with or without 10 mM EDTA, or PBS as control, were incubated at 37°C for 3 min.  After incubation, samples were AO-stained and amastigotes associated with two or more erythrocytes counted as IA rosettes. A, amastigotes; E, erythrocytes. Data are expressed as the mean values of duplicate samples. Similar results were obtained in two individual experiments.
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Figure 5: Amastigote IA. (A) AO-stained amastigote rosettes with human erythrocytes. Rosettes were formed as described in Materials and Methods. After incubation, samples were stained and photographed (×790). (B) Amastigote IA reaction. 50-μl aliquots each of a 10% washed erythrocyte suspension, L. amazonensis amastigotes (2 × 107 cells/ml), and 33% NHS with or without 10 mM EDTA, or PBS as control, were incubated at 37°C for 3 min. After incubation, samples were AO-stained and amastigotes associated with two or more erythrocytes counted as IA rosettes. A, amastigotes; E, erythrocytes. Data are expressed as the mean values of duplicate samples. Similar results were obtained in two individual experiments.

Mentions: To determine whether amastigotes also undergo IA, they were isolated from L. amazonensis–infected BALB/c mice and incubated with washed erythrocytes and NHS as described in method B. NHS was replaced by either PBS or EDTA-treated NHS in control samples. After incubation, amastigotes were stained with AO and those with three or more bound erythrocytes were counted as IA rosettes (Fig. 5 A). More than 90% of amastigotes were attached to erythrocytes after 3 min of incubation (Fig. 5 B), whereas no reaction was observed in controls.


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

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

Amastigote IA. (A) AO-stained amastigote rosettes with human erythrocytes. Rosettes were formed as described in Materials and Methods.  After incubation, samples were stained and photographed (×790). (B) Amastigote IA reaction. 50-μl aliquots each of a 10% washed erythrocyte suspension, L. amazonensis amastigotes (2 × 107 cells/ml), and 33% NHS with or without 10 mM EDTA, or PBS as control, were incubated at 37°C for 3 min.  After incubation, samples were AO-stained and amastigotes associated with two or more erythrocytes counted as IA rosettes. A, amastigotes; E, erythrocytes. Data are expressed as the mean values of duplicate samples. Similar results were obtained in two individual experiments.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 5: Amastigote IA. (A) AO-stained amastigote rosettes with human erythrocytes. Rosettes were formed as described in Materials and Methods. After incubation, samples were stained and photographed (×790). (B) Amastigote IA reaction. 50-μl aliquots each of a 10% washed erythrocyte suspension, L. amazonensis amastigotes (2 × 107 cells/ml), and 33% NHS with or without 10 mM EDTA, or PBS as control, were incubated at 37°C for 3 min. After incubation, samples were AO-stained and amastigotes associated with two or more erythrocytes counted as IA rosettes. A, amastigotes; E, erythrocytes. Data are expressed as the mean values of duplicate samples. Similar results were obtained in two individual experiments.
Mentions: To determine whether amastigotes also undergo IA, they were isolated from L. amazonensis–infected BALB/c mice and incubated with washed erythrocytes and NHS as described in method B. NHS was replaced by either PBS or EDTA-treated NHS in control samples. After incubation, amastigotes were stained with AO and those with three or more bound erythrocytes were counted as IA rosettes (Fig. 5 A). More than 90% of amastigotes were attached to erythrocytes after 3 min of incubation (Fig. 5 B), whereas no reaction was observed in controls.

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