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Apoptosis in Hemocytes Induces a Shift in Effector Mechanisms in the Drosophila Immune System and Leads to a Pro-Inflammatory State.

Arefin B, Kucerova L, Krautz R, Kranenburg H, Parvin F, Theopold U - PLoS ONE (2015)

Bottom Line: Surprisingly, we found that Hml-apo larvae are still resistant to nematode infections.When further elucidating the immune status of Hml-apo larvae, we observe a shift in immune effector pathways including massive lamellocyte differentiation and induction of Toll- as well as repression of imd signaling.Finally we show that the nitric oxide donor L-arginine similarly modifies the response against an early stage of tumor development in fly larvae.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biosciences, Wenner-Gren Institute, Stockholm University, Stockholm, Sweden.

ABSTRACT
Apart from their role in cellular immunity via phagocytosis and encapsulation, Drosophila hemocytes release soluble factors such as antimicrobial peptides, and cytokines to induce humoral responses. In addition, they participate in coagulation and wounding, and in development. To assess their role during infection with entomopathogenic nematodes, we depleted plasmatocytes and crystal cells, the two classes of hemocytes present in naïve larvae by expressing proapoptotic proteins in order to produce hemocyte-free (Hml-apo, originally called Hemoless) larvae. Surprisingly, we found that Hml-apo larvae are still resistant to nematode infections. When further elucidating the immune status of Hml-apo larvae, we observe a shift in immune effector pathways including massive lamellocyte differentiation and induction of Toll- as well as repression of imd signaling. This leads to a pro-inflammatory state, characterized by the appearance of melanotic nodules in the hemolymph and to strong developmental defects including pupal lethality and leg defects in escapers. Further analysis suggests that most of the phenotypes we observe in Hml-apo larvae are alleviated by administration of antibiotics and by changing the food source indicating that they are mediated through the microbiota. Biochemical evidence identifies nitric oxide as a key phylogenetically conserved regulator in this process. Finally we show that the nitric oxide donor L-arginine similarly modifies the response against an early stage of tumor development in fly larvae.

No MeSH data available.


Related in: MedlinePlus

Melanotic masses are formed in Hid- and Grim-expressing larvae.(A-B’’’) Different patterns of melanotic masses were found in both Hid- (A-A’) and Grim-expressing larvae (B-B’’’). (C-E) The melanotic mass of the area marked in B’’’ was visualized at higher magnification (C-E). GFP-positive hemocytes were observed within the melanotic mass (D) indicating hemocyte origin. (F-H) Melanotic masses from Hid-expressing larvae also displayed a GFP signal (G) as in (D). (G). Of note, Hid expression was found stronger than Grim. (I) Positive correlation between larval frequency (melanotic spot) and lamellocyte numbers in different Hid and Grim lines (Spearman correlation, P value = 0.0108).
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pone.0136593.g005: Melanotic masses are formed in Hid- and Grim-expressing larvae.(A-B’’’) Different patterns of melanotic masses were found in both Hid- (A-A’) and Grim-expressing larvae (B-B’’’). (C-E) The melanotic mass of the area marked in B’’’ was visualized at higher magnification (C-E). GFP-positive hemocytes were observed within the melanotic mass (D) indicating hemocyte origin. (F-H) Melanotic masses from Hid-expressing larvae also displayed a GFP signal (G) as in (D). (G). Of note, Hid expression was found stronger than Grim. (I) Positive correlation between larval frequency (melanotic spot) and lamellocyte numbers in different Hid and Grim lines (Spearman correlation, P value = 0.0108).

Mentions: We observed melanotic masses or pseudo-tumors in Hml-apo larvae at late 3rd instar larval stages leading to different patterns (Fig 5A and 5B”). These melanotic aggregates were found in both the anterior and posterior part of the larva and in circulation. To test whether melanization targets any particular organ, we dissected larvae but did not observe any organ-specific pattern. Instead melanotic masses appeared loosely attached to the fore- and hindgut. When they were analyzed microscopically (Fig 5C–5H), some GFP-positive cells were detected indicating that they were at least partially of hemocyte origin. When plotted against lamellocyte numbers the frequency of the melanotic aggregates clearly showed a positive correlation (Fig 5I) (P value = 0.0067) indicating that melanization might depend on lamellocyte phenoloxidase (PPO3) or that lamellocyte differentiation and melanization are co-regulated.


Apoptosis in Hemocytes Induces a Shift in Effector Mechanisms in the Drosophila Immune System and Leads to a Pro-Inflammatory State.

Arefin B, Kucerova L, Krautz R, Kranenburg H, Parvin F, Theopold U - PLoS ONE (2015)

Melanotic masses are formed in Hid- and Grim-expressing larvae.(A-B’’’) Different patterns of melanotic masses were found in both Hid- (A-A’) and Grim-expressing larvae (B-B’’’). (C-E) The melanotic mass of the area marked in B’’’ was visualized at higher magnification (C-E). GFP-positive hemocytes were observed within the melanotic mass (D) indicating hemocyte origin. (F-H) Melanotic masses from Hid-expressing larvae also displayed a GFP signal (G) as in (D). (G). Of note, Hid expression was found stronger than Grim. (I) Positive correlation between larval frequency (melanotic spot) and lamellocyte numbers in different Hid and Grim lines (Spearman correlation, P value = 0.0108).
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4555835&req=5

pone.0136593.g005: Melanotic masses are formed in Hid- and Grim-expressing larvae.(A-B’’’) Different patterns of melanotic masses were found in both Hid- (A-A’) and Grim-expressing larvae (B-B’’’). (C-E) The melanotic mass of the area marked in B’’’ was visualized at higher magnification (C-E). GFP-positive hemocytes were observed within the melanotic mass (D) indicating hemocyte origin. (F-H) Melanotic masses from Hid-expressing larvae also displayed a GFP signal (G) as in (D). (G). Of note, Hid expression was found stronger than Grim. (I) Positive correlation between larval frequency (melanotic spot) and lamellocyte numbers in different Hid and Grim lines (Spearman correlation, P value = 0.0108).
Mentions: We observed melanotic masses or pseudo-tumors in Hml-apo larvae at late 3rd instar larval stages leading to different patterns (Fig 5A and 5B”). These melanotic aggregates were found in both the anterior and posterior part of the larva and in circulation. To test whether melanization targets any particular organ, we dissected larvae but did not observe any organ-specific pattern. Instead melanotic masses appeared loosely attached to the fore- and hindgut. When they were analyzed microscopically (Fig 5C–5H), some GFP-positive cells were detected indicating that they were at least partially of hemocyte origin. When plotted against lamellocyte numbers the frequency of the melanotic aggregates clearly showed a positive correlation (Fig 5I) (P value = 0.0067) indicating that melanization might depend on lamellocyte phenoloxidase (PPO3) or that lamellocyte differentiation and melanization are co-regulated.

Bottom Line: Surprisingly, we found that Hml-apo larvae are still resistant to nematode infections.When further elucidating the immune status of Hml-apo larvae, we observe a shift in immune effector pathways including massive lamellocyte differentiation and induction of Toll- as well as repression of imd signaling.Finally we show that the nitric oxide donor L-arginine similarly modifies the response against an early stage of tumor development in fly larvae.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biosciences, Wenner-Gren Institute, Stockholm University, Stockholm, Sweden.

ABSTRACT
Apart from their role in cellular immunity via phagocytosis and encapsulation, Drosophila hemocytes release soluble factors such as antimicrobial peptides, and cytokines to induce humoral responses. In addition, they participate in coagulation and wounding, and in development. To assess their role during infection with entomopathogenic nematodes, we depleted plasmatocytes and crystal cells, the two classes of hemocytes present in naïve larvae by expressing proapoptotic proteins in order to produce hemocyte-free (Hml-apo, originally called Hemoless) larvae. Surprisingly, we found that Hml-apo larvae are still resistant to nematode infections. When further elucidating the immune status of Hml-apo larvae, we observe a shift in immune effector pathways including massive lamellocyte differentiation and induction of Toll- as well as repression of imd signaling. This leads to a pro-inflammatory state, characterized by the appearance of melanotic nodules in the hemolymph and to strong developmental defects including pupal lethality and leg defects in escapers. Further analysis suggests that most of the phenotypes we observe in Hml-apo larvae are alleviated by administration of antibiotics and by changing the food source indicating that they are mediated through the microbiota. Biochemical evidence identifies nitric oxide as a key phylogenetically conserved regulator in this process. Finally we show that the nitric oxide donor L-arginine similarly modifies the response against an early stage of tumor development in fly larvae.

No MeSH data available.


Related in: MedlinePlus