Inflammatory manifestations of experimental lymphatic insufficiency

Background Sustained lymph stagnation engenders a pathological response that is complex and not well characterized. Tissue inflammation in lymphedema may reflect either an active or passive consequence of impaired immune traffic. Methods and Findings We studied an experimental model of acute post-surgical lymphedema in the tails of female hairless, immunocompetent SKH-1 mice. We performed in vivo imaging of impaired immune traffic in experimental, murine acquired lymphatic insufficiency. We demonstrated impaired mobilization of immunocompetent cells from the lymphedematous region. These findings correlated with histopathological alterations and large-scale transcriptional profiling results. We found intense inflammatory changes in the dermis and the subdermis. The molecular pattern in the RNA extracted from the whole tissue was dominated by the upregulation of genes related to acute inflammation, immune response, complement activation, wound healing, fibrosis, and oxidative stress response. Conclusions We have characterized a mouse model of acute, acquired lymphedema using in vivo functional imaging and histopathological correlation. The model closely simulates the volume response, histopathology, and lymphoscintigraphic characteristics of human acquired lymphedema, and the response is accompanied by an increase in the number and size of microlymphatic structures in the lymphedematous cutaneous tissues. Molecular characterization through clustering of genes with known functions provides insights into processes and signaling pathways that compose the acute tissue response to lymph stagnation. Further study of genes identified through this effort will continue to elucidate the molecular mechanisms and lead to potential therapeutic strategies for lymphatic vascular insufficiency.
Editors' Summary Background. Lymphedema is the term used to describe the swelling that can occur after surgery, especially after axillary lymph node dissection for breast cancer, when the lymph vessels that carry protein-rich interstitial fluid from the tissues to the heart are damaged. Lymphedema can be extremely unpleasant and is very hard to treat; treatments that are currently used include those aimed to help massage the flow of lymph back to the chest. Lymphedema seems to be more than just accumulation of lymph, however, as changes also occur in the tissue surrounding the damaged lymph vessels. Currently, very little is known at the most basic level about what exactly these changes are, although they appear to be similar to an inflammatory process. One way of studying such a disease process in humans is to make an animal model that mimics the human condition and study the changes that occur there. For lymphedema, such a model can be made in the mouse tail by cutting lymph vessels there. Why Was This Study Done? The authors wanted to look closely at what happens in the tissues surrounding damaged lymph vessels to try to understand better what these changes are. They also wanted to study the movement of the cells that are normally carried in the lymph. What Did the Researchers Do and Find? The mouse model that the authors developed closely simulates the characteristics of human acquired lymphedema. In the mouse tails that had had their lymph vessels damaged, the authors were able to show that the tails were swollen compared with those of normal animals and of animals that hadhad sham (pretend) surgery. In the animals with lymphedema, many small lymph vessels were seen, as the lymph was unable to flow away normally. The area affected by the lymphedema had the appearance often seen in inflamed tissue, and analysis of genes from the same area to see how active, or “expressed,” they were showed changes that are often seen in, for example, acute inflammation and wound healing. The authors also showed that when these animals were injected with immune cells marked with a light marker, they were less able to remove the cells from the circulation. What Do These Findings Mean? These results show that the response to lymph stagnation is complex, but looks similar to that seen in acute inflammation. These results and this model may be useful in suggesting, and at a later date perhaps testing, treatments for lymphedema. One difference, however, between this mouse model and the condition in humans is that whereas lymphedema in humans is a rather chronic condition, here the researchers were only able to look at the changes over a short period of time. In a related Perspective article, Peter Carmeliet and colleagues further discuss the clinical relevance of these findings ( http://dx.doi.org/10.1371/journal.pmed.0030264). Additional Information. Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0030254. • The National Cancer Institute has information for patients and health professionals on lymphedema • Cancerbackup is a United Kingdom cancer information service with information on many aspects of cancer, including lymphedema • The Lymphatic Research Foundation Description has information on lymphatic system research
Rockson and colleagues characterized a mouse model of acute, acquired lymphedema using in vivo functional imaging, histopathological examination, and transcriptional profiling.