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Migratory dermal dendritic cells act as rapid sensors of protozoan parasites.

Ng LG, Hsu A, Mandell MA, Roediger B, Hoeller C, Mrass P, Iparraguirre A, Cavanagh LL, Triccas JA, Beverley SM, Scott P, Weninger W - PLoS Pathog. (2008)

Bottom Line: Surprisingly, we found that, under homeostatic conditions, DDC were highly motile, continuously crawling through the interstitial space in a Galpha(i) protein-coupled receptor-dependent manner.Together, our study has visualized the dynamics and microenvironmental context of parasite encounter by an innate immune cell subset during the initiation of the immune response.Our results uncover a unique migratory tissue surveillance program of DDC that ensures the rapid detection of pathogens.

View Article: PubMed Central - PubMed

Affiliation: The Wistar Institute, Philadelphia, Pennsylvania, USA.

ABSTRACT
Dendritic cells (DC), including those of the skin, act as sentinels for intruding microorganisms. In the epidermis, DC (termed Langerhans cells, LC) are sessile and screen their microenvironment through occasional movements of their dendrites. The spatio-temporal orchestration of antigen encounter by dermal DC (DDC) is not known. Since these cells are thought to be instrumental in the initiation of immune responses during infection, we investigated their behavior directly within their natural microenvironment using intravital two-photon microscopy. Surprisingly, we found that, under homeostatic conditions, DDC were highly motile, continuously crawling through the interstitial space in a Galpha(i) protein-coupled receptor-dependent manner. However, within minutes after intradermal delivery of the protozoan parasite Leishmania major, DDC became immobile and incorporated multiple parasites into cytosolic vacuoles. Parasite uptake occurred through the extension of long, highly dynamic pseudopods capable of tracking and engulfing parasites. This was then followed by rapid dendrite retraction towards the cell body. DDC were proficient at discriminating between parasites and inert particles, and parasite uptake was independent of the presence of neutrophils. Together, our study has visualized the dynamics and microenvironmental context of parasite encounter by an innate immune cell subset during the initiation of the immune response. Our results uncover a unique migratory tissue surveillance program of DDC that ensures the rapid detection of pathogens.

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Internalization of L. major by DDC.(A) Three-dimensional reconstructions of ear skin inoculated with LmjF-DsRed2 promastigotes (red) showing the distribution of parasites (90 serial optical sections, 1 µm step size). (B) Representative images showing the morphology of LC (epidermis, yellow) and DDC (dermis, yellow) after LmjF-DsRed2 promastigote (red) inoculation. (C) A three-dimensional section of DDC (yellow) containing intracellular LmjF-DsRed2 promastigotes (red). Plot shows the frequency of LC and DDC containing LmjF or LV39 parasites (>50 cells obtained from randomly selected fields). (D) Comparison of the mean velocity and displacement of DDC in control skin, and DDC in infected skin with or without internalized parasites. Data points represent individual cells, lines indicate mean. Data were obtained from at least three independent experiments. (E) SNARF-1 was injected i.d. and DDC migration determined after 2 h (n = 3 experiments). Symbols represent individual cells. Control data are the same as in Figure 4A.
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ppat-1000222-g005: Internalization of L. major by DDC.(A) Three-dimensional reconstructions of ear skin inoculated with LmjF-DsRed2 promastigotes (red) showing the distribution of parasites (90 serial optical sections, 1 µm step size). (B) Representative images showing the morphology of LC (epidermis, yellow) and DDC (dermis, yellow) after LmjF-DsRed2 promastigote (red) inoculation. (C) A three-dimensional section of DDC (yellow) containing intracellular LmjF-DsRed2 promastigotes (red). Plot shows the frequency of LC and DDC containing LmjF or LV39 parasites (>50 cells obtained from randomly selected fields). (D) Comparison of the mean velocity and displacement of DDC in control skin, and DDC in infected skin with or without internalized parasites. Data points represent individual cells, lines indicate mean. Data were obtained from at least three independent experiments. (E) SNARF-1 was injected i.d. and DDC migration determined after 2 h (n = 3 experiments). Symbols represent individual cells. Control data are the same as in Figure 4A.

Mentions: 1–2×105 DsRed2-tagged Leishmania (LmjF-DsRed2) promastigotes were injected in a small volume (1.5 µl) of saline solution into the superficial dermis. This allowed us to deposit parasites underneath the epidermis at a vertical depth of 25–60 µm while keeping mechanical tissue disruption as minimal as possible (Figure 5A). Within 20 min of injection, DDC in the vicinity of parasites decreased their migratory speed and changed their shape to a more dendritic cell-like morphology characterized by the emergence of multiple dendritic processes (Figure 5B and 5C). This was paralleled by the appearance of several intracellular vacuoles, each of them containing a single red parasite (Figure 5C), which is consistent with the formation of PVs [26],[27]. Interestingly, these vacuoles were mobile, i.e. appeared to move freely within the cytoplasm of the cells. Two to three hours after infection, the percentage of DDC harboring one or more parasite was ∼70% (Figure 5C). Of note, LC morphology and behavior was unchanged after infection with L. major. Further, LC were not found to take up parasites, at least during the first six hours of infection (data not shown). However, it should be pointed out that parasites were injected intradermally. Consequently, LC access to parasites may have been prevented by anatomical barriers, such as the epidermal basement membrane.


Migratory dermal dendritic cells act as rapid sensors of protozoan parasites.

Ng LG, Hsu A, Mandell MA, Roediger B, Hoeller C, Mrass P, Iparraguirre A, Cavanagh LL, Triccas JA, Beverley SM, Scott P, Weninger W - PLoS Pathog. (2008)

Internalization of L. major by DDC.(A) Three-dimensional reconstructions of ear skin inoculated with LmjF-DsRed2 promastigotes (red) showing the distribution of parasites (90 serial optical sections, 1 µm step size). (B) Representative images showing the morphology of LC (epidermis, yellow) and DDC (dermis, yellow) after LmjF-DsRed2 promastigote (red) inoculation. (C) A three-dimensional section of DDC (yellow) containing intracellular LmjF-DsRed2 promastigotes (red). Plot shows the frequency of LC and DDC containing LmjF or LV39 parasites (>50 cells obtained from randomly selected fields). (D) Comparison of the mean velocity and displacement of DDC in control skin, and DDC in infected skin with or without internalized parasites. Data points represent individual cells, lines indicate mean. Data were obtained from at least three independent experiments. (E) SNARF-1 was injected i.d. and DDC migration determined after 2 h (n = 3 experiments). Symbols represent individual cells. Control data are the same as in Figure 4A.
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Related In: Results  -  Collection

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ppat-1000222-g005: Internalization of L. major by DDC.(A) Three-dimensional reconstructions of ear skin inoculated with LmjF-DsRed2 promastigotes (red) showing the distribution of parasites (90 serial optical sections, 1 µm step size). (B) Representative images showing the morphology of LC (epidermis, yellow) and DDC (dermis, yellow) after LmjF-DsRed2 promastigote (red) inoculation. (C) A three-dimensional section of DDC (yellow) containing intracellular LmjF-DsRed2 promastigotes (red). Plot shows the frequency of LC and DDC containing LmjF or LV39 parasites (>50 cells obtained from randomly selected fields). (D) Comparison of the mean velocity and displacement of DDC in control skin, and DDC in infected skin with or without internalized parasites. Data points represent individual cells, lines indicate mean. Data were obtained from at least three independent experiments. (E) SNARF-1 was injected i.d. and DDC migration determined after 2 h (n = 3 experiments). Symbols represent individual cells. Control data are the same as in Figure 4A.
Mentions: 1–2×105 DsRed2-tagged Leishmania (LmjF-DsRed2) promastigotes were injected in a small volume (1.5 µl) of saline solution into the superficial dermis. This allowed us to deposit parasites underneath the epidermis at a vertical depth of 25–60 µm while keeping mechanical tissue disruption as minimal as possible (Figure 5A). Within 20 min of injection, DDC in the vicinity of parasites decreased their migratory speed and changed their shape to a more dendritic cell-like morphology characterized by the emergence of multiple dendritic processes (Figure 5B and 5C). This was paralleled by the appearance of several intracellular vacuoles, each of them containing a single red parasite (Figure 5C), which is consistent with the formation of PVs [26],[27]. Interestingly, these vacuoles were mobile, i.e. appeared to move freely within the cytoplasm of the cells. Two to three hours after infection, the percentage of DDC harboring one or more parasite was ∼70% (Figure 5C). Of note, LC morphology and behavior was unchanged after infection with L. major. Further, LC were not found to take up parasites, at least during the first six hours of infection (data not shown). However, it should be pointed out that parasites were injected intradermally. Consequently, LC access to parasites may have been prevented by anatomical barriers, such as the epidermal basement membrane.

Bottom Line: Surprisingly, we found that, under homeostatic conditions, DDC were highly motile, continuously crawling through the interstitial space in a Galpha(i) protein-coupled receptor-dependent manner.Together, our study has visualized the dynamics and microenvironmental context of parasite encounter by an innate immune cell subset during the initiation of the immune response.Our results uncover a unique migratory tissue surveillance program of DDC that ensures the rapid detection of pathogens.

View Article: PubMed Central - PubMed

Affiliation: The Wistar Institute, Philadelphia, Pennsylvania, USA.

ABSTRACT
Dendritic cells (DC), including those of the skin, act as sentinels for intruding microorganisms. In the epidermis, DC (termed Langerhans cells, LC) are sessile and screen their microenvironment through occasional movements of their dendrites. The spatio-temporal orchestration of antigen encounter by dermal DC (DDC) is not known. Since these cells are thought to be instrumental in the initiation of immune responses during infection, we investigated their behavior directly within their natural microenvironment using intravital two-photon microscopy. Surprisingly, we found that, under homeostatic conditions, DDC were highly motile, continuously crawling through the interstitial space in a Galpha(i) protein-coupled receptor-dependent manner. However, within minutes after intradermal delivery of the protozoan parasite Leishmania major, DDC became immobile and incorporated multiple parasites into cytosolic vacuoles. Parasite uptake occurred through the extension of long, highly dynamic pseudopods capable of tracking and engulfing parasites. This was then followed by rapid dendrite retraction towards the cell body. DDC were proficient at discriminating between parasites and inert particles, and parasite uptake was independent of the presence of neutrophils. Together, our study has visualized the dynamics and microenvironmental context of parasite encounter by an innate immune cell subset during the initiation of the immune response. Our results uncover a unique migratory tissue surveillance program of DDC that ensures the rapid detection of pathogens.

Show MeSH
Related in: MedlinePlus