Haemocytes control stem cell activity in the Drosophila intestine.

Coordination of stem cell activity with inflammatory responses is critical for regeneration and homeostasis of barrier epithelia. The temporal sequence of cell interactions during injury-induced regeneration is only beginning to be understood. Here we show that intestinal stem cells (ISCs) are regulated by macrophage-like haemocytes during the early phase of regenerative responses of the Drosophila intestinal epithelium. On tissue damage, haemocytes are recruited to the intestine and secrete the BMP homologue DPP, inducing ISC proliferation by activating the type I receptor Saxophone and the Smad homologue SMOX. Activated ISCs then switch their response to DPP by inducing expression of Thickveins, a second type I receptor that has previously been shown to re-establish ISC quiescence by activating MAD. The interaction between haemocytes and ISCs promotes infection resistance, but also contributes to the development of intestinal dysplasia in ageing flies. We propose that similar interactions influence pathologies such as inflammatory bowel disease and colorectal cancer in humans.

Obligate symbionts activate immune system development in the tsetse fly.

Many insects rely on the presence of symbiotic bacteria for proper immune system function. However, the molecular mechanisms that underlie this phenomenon are poorly understood. Adult tsetse flies (Glossina spp.) house three symbiotic bacteria that are vertically transmitted from mother to offspring during this insect's unique viviparous mode of reproduction. Larval tsetse that undergo intrauterine development in the absence of their obligate mutualist, Wigglesworthia, exhibit a compromised immune system during adulthood. In this study, we characterize the immune phenotype of tsetse that develop in the absence of all of their endogenous symbiotic microbes. Aposymbiotic tsetse (Glossina morsitans morsitans [Gmm(Apo)]) present a severely compromised immune system that is characterized by the absence of phagocytic hemocytes and atypical expression of immunity-related genes. Correspondingly, these flies quickly succumb to infection with normally nonpathogenic Escherichia coli. The susceptible phenotype exhibited by Gmm(Apo) adults can be reversed when they receive hemocytes transplanted from wild-type donor flies prior to infection. Furthermore, the process of immune system development can be restored in intrauterine Gmm(Apo) larvae when their mothers are fed a diet supplemented with Wigglesworthia cell extracts. Our finding that molecular components of Wigglesworthia exhibit immunostimulatory activity within tsetse is representative of a novel evolutionary adaptation that steadfastly links an obligate symbiont with its host.

Sessile hemocytes as a hematopoietic compartment in Drosophila melanogaster.

The blood cells, or hemocytes, in Drosophila participate in the immune response through the production of antimicrobial peptides, the phagocytosis of bacteria, and the encapsulation of larger foreign particles such as parasitic eggs; these immune reactions are mediated by phylogenetically conserved mechanisms. The encapsulation reaction is analogous to the formation of granuloma in vertebrates, and is mediated by large specialized cells, the lamellocytes. The origin of the lamellocytes has not been formally established, although it has been suggested that they are derived from the lymph gland, which is generally considered to be the main hematopoietic organ in the Drosophila larva. However, it was recently observed that a subepidermal population of sessile blood cells is released into the circulation in response to a parasitoid wasp infection. We set out to analyze this phenomenon systematically. As a result, we define the sessile hemocytes as a novel hematopoietic compartment, and the main source of lamellocytes.

Selective percutaneous desiccation of the perforators with radiofrequency for strategic transfer of angiosomes in a sequential four-territory cutaneous island flap model.

BACKGROUND: Research in prevention of partial flap necrosis has recently concentrated on extending the safe length of a flap by ligating vessels of known territories. To advance this approach one step further, the authors decided to reveal the least invasive surgical strategy for transfer of angiosomes. METHODS: The study was arranged into three experiments. In the first experiment (n = 17 rabbits), a cutaneous island flap model spanning four adjacent vascular territories was developed. In the second experiment (n = 15 rabbits), the flap model was used to test the possibility of desiccating those vessels supplying the angiosomes to be captured percutaneously with radiofrequency. The delay procedures were performed by means of minimal skin incisions, and the flaps were elevated after a 2-week delay period. In the third experiment, the effectiveness of selective interference of these pedicles was compared to minimize the number of target vessels for successful transfer of angiosomes. RESULTS: The mean surviving area of the new flap model was 63 +/- 2 percent. The mean surviving flap area was 97 +/- 3 percent for the endoscopy equivalent technique and 94 +/- 4 percent for radiofrequency delay. The results were statistically insignificant between these two groups. In experiment 3, comparison of the results yielded a statistically insignificant difference for flap survival area among all four of the groups. CONCLUSIONS: An alternative flap model is introduced for future investigation of the vascular delay process. Percutaneous desiccation of the perforators with radiofrequency was found to be a reliable method, and selective desiccation of the perforator(s) was as efficient as destruction of all vascular sources other than the pedicle.

Killing of Schistosoma mansoni sporocysts in Biomphalaria glabrata implanted with amoebocyte-producing organ allografts from resistant snails.

Schistosome-susceptible National Institutes of Health (NIH) albino Biomphalaria glabrata were implanted with the amoebocyte-producing organ (APO) from 4 types of donors: (1) exposed-resistant (eR), i.e., schistosome-resistant 13-16-R1 snails that had been exposed to miracidia of Schistosoma mansoni 30 or more days previously in order to verify their resistance, (2) exposed-susceptible (eS), i.e., NIH albino snails that had been similarly exposed to miracidia, (3) unexposed-resistant (uR), and (4) unexposed-susceptible (uS). Allograft recipients, along with unimplanted NIH albino and 13-16-R1 controls (cS and cR, respectively), were then challenged with 100 miracidia each of Schistosoma mansoni at 14-15 days postimplantation. Histological sections of tentacles fixed at 3 days postchallenge (PC) showed significantly fewer normal sporocysts and more numerous developmentally retarded sporocysts in cR snails than in the other 5 treatment groups, and significantly more killed sporocysts in both cR snails and recipients of eR APOs than in the other 4 groups. In addition, the histological condition of eR allografts in both unchallenged (at 1, 3, 7, 10, and 14 days postimplantation) and schistosome-challenged (at 3 days PC) NIH albino recipients was examined. Viable hematopoietic cells were found in 96% of implants, and in 86% of implants low numbers of mitotic figures were found among these cells, although no increased mitotic activity occurred in challenged recipients. These data suggest that lowered susceptibility to infection with S. mansoni in recipients of APO allografts results primarily from hemocyte-mediated resistance.

Proliferation of lymphocyte-like cells from the solitary tunicate, Styela clava, in response to allogeneic stimuli.

Lymphocyte-like hemocytes (LLCs) of solitary tunicates proliferate in response to allogeneic stimuli. In vitro labeling of proliferative hemocytes from the solitary species Styela clava revealed significantly greater proliferative activity among individuals immunized with allogeneic tissue as opposed to autogeneically primed and naïve animals. Enhanced proliferation was restricted to discrete crypts of dividing cells within the body wall of recipients. Here, increased proliferative activity was specifically associated with LLCs. These data support previous results which implicated LLC activity with immunological memory that is evident in allograft rejection. Hence, it is postulated that adaptive histoincompatibility responses in solitary tunicates depend upon the specific proliferation of immunocompetent cells.

Demonstration of cell-mediated cytotoxicity to allogeneic and xenogeneic tissue in the American cockroach, Periplaneta americana, using a combination in vivo/in vitro assay.

Previous reports have claimed that insects lack the ability to reject integumentary allografts. However, when we followed the fate of the epidermal layer underneath the inert cuticle, we observed that the American cockroach not only rejected xenografts, but also demonstrated impressive reactivity against allografts. We have now developed a combination in vivo/in vitro assay that can quantitate the extent of allograft reactivity in the roach. Pieces of filter paper (3 X 4-mm) were implanted under the second and fourth tergites of donor animals. After 7 days, implants seeded with host hemocytes were removed, washed, and incubated in culture medium containing 3H-thymidine for 24 hr. Labeled grafts were reimplanted into paired animals to detect cytotoxicity as follows: grafts removed from under the second tergite were placed back into their original positions to serve as autograft controls; grafts removed from under the fourth tergite were reciprocally transferred between paired animals; and grafts were recovered after various time intervals and processed for scintillation counting. There was no significant difference in counts between allografts and autografts at day 1. Autografts sampled on days 3, 5, 7, and 10 had significantly higher counts than allografts, with peak reactivity occurring between days 3 and 5. This indicates that allogeneic cells were selectively destroyed, and confirms our recent data from conventional grafting studies that insects have the ability to react to allografts.