Carrying yourself: self antigen composition of the lymphatic fluid

Acute exposure to space flight results in evidence of reduced lymph Transport, tissue fluid Shifts, and immune alterations in the rat gastrointestinal system

Space flight causes a number of alterations in physiological systems, changes in the immunological status of subjects, and altered interactions of the host to environmental stimuli. We studied the effect of space flight on the lymphatic system of the gastrointestinal tract which is responsible for lipid transport and immune surveillance which includes the host interaction with the gut microbiome. We found that there were signs of tissue damage present in the space flown animals that was lacking in ground controls (epithelial damage, crypt morphological changes, etc.). Additionally, morphology of the lymphatic vessels in the tissue suggested a collapsed state at time of harvest and there was a profound change in the retention of lipid in the villi of the ileum. Contrary to our assumptions there was a reduction in tissue fluid volume likely associated with other fluid shifts described. The reduction of tissue fluid volume in the colon and ileum is a likely contributing factor to the state of the lymphatic vessels and lipid transport issues observed. There were also associated changes in the number of MHC-II⁺ immune cells in the colon tissue, which along with reduced lymphatic competence would favor immune dysfunction in the tissue. These findings help expand our understanding of the effects of space flight on various organ systems. It also points out potential issues that have not been closely examined and have to potential for the need of countermeasure development.

Exploiting lymphatic vessels for immunomodulation: Rationale, opportunities, and challenges

Lymphatic vessels are the primary route of communication from peripheral tissues to the immune system; as such, they represent an important component of local immunity. In addition to their transport functions, new immunomodulatory roles for lymphatic vessels and lymphatic endothelial cells have come to light in recent years, demonstrating that lymphatic vessels help shape immune responses in a variety of ways: promoting tolerance to self-antigens, archiving antigen for later presentation, dampening effector immune responses, and resolving inflammation, among others. In addition to these new biological insights, the growing field of immunoengineering has begun to explore therapeutic approaches to utilize or exploit the lymphatic system for immunotherapy.

Modes of Antigen Presentation by Lymph Node Stromal Cells and Their Immunological Implications

Antigen presentation is no longer the exclusive domain of cells of hematopoietic origin. Recent works have demonstrated that lymph node stromal cell (LNSC) populations, such as fibroblastic reticular cells, lymphatic and blood endothelial cells, not only provide a scaffold for lymphocyte interactions but also exhibit active immunomodulatory roles that are critical to mounting and resolving effective immune responses. Importantly, LNSCs possess the ability to present antigens and establish antigen-specific interactions with T cells. One example is the expression of peripheral tissue antigens, which are presented on major histocompatibility complex (MHC)-I molecules with tolerogenic consequences on T cells. Additionally, exogenous antigens, including self and tumor antigens, can be processed and presented on MHC-I complexes, which result in dysfunctional activation of antigen-specific CD8⁺ T cells. While MHC-I is widely expressed on cells of both hematopoietic and non-hematopoietic origins, antigen presentation via MHC-II is more precisely regulated. Nevertheless, LNSCs are capable of endogenously expressing, or alternatively, acquiring MHC-II molecules. Transfer of antigen between LNSC and dendritic cells in both directions has been recently suggested to promote tolerogenic roles of LNSCs on the CD4⁺ T cell compartment. Thus, antigen presentation by LNSCs is thought to be a mechanism that promotes the maintenance of peripheral tolerance as well as generates a pool of diverse antigen-experienced T cells for protective immunity. This review aims to integrate the current and emerging literature to highlight the importance of LNSCs in immune responses, and emphasize their role in antigen trafficking, retention, and presentation.

Lymph is not a plasma ultrafiltrate: a proteomic analysis of injured patients

Studies on animal models have documented a role for the water-soluble protein fraction of mesenteric lymph as a conduit from hemorrhagic shock to acute lung injury and postinjury multiple organ failure. We hypothesize that mesenteric lymph is not an ultrafiltrate of plasma and contains specific protein mediators that may predispose patients to acute lung injury/multiple organ failure. Mesenteric lymph and plasma were collected from critically ill or injured patients and from nine patients with lymphatic injuries, during semielective spine reconstruction, or immediately before organ donation. Proteomic analyses were performed through immunoaffinity depletion of the 14 most abundant plasma proteins and 1D gel electrophoresis followed by liquid chromatography coupled online with mass spectrometry analyses. Overall, 548 proteins were identified in the patients undergoing semielective surgery, of which 155 were uniquely present in the lymph. In addition, the postshock plasma proteome was characterized by peculiar features, suggesting that only a partial overlap exists between the plasma and mesenteric lymph from trauma patients. Differential proteins between the matched plasma and mesenteric lymph from trauma patients could be related to coagulopathy and hypercoagulability, cell lysis, proinflammatory responses and immune system activation, extracellular matrix remodeling, lymph-specific immunomodulation and vascular hypoactivity/neoangiogenesis, and energy/redox metabolic adaptation to trauma. In conclusion, the proteome of mesenteric lymph is biologically different (in qualitative and quantitative terms) than that of a mere plasma ultrafiltrate.

Colonic Insult Impairs Lymph Flow, Increases Cellular Content of the Lymph, Alters Local Lymphatic Microenvironment, and Leads to Sustained Inflammation in the Rat Ileum

BACKGROUND

Lymphatic dysfunction has been linked to inflammation since the 1930s. Lymphatic function in the gut and mesentery is grossly underexplored in models of inflammatory bowel disease despite the use of lymphatic occlusion in early models of inflammatory bowel disease. Activation of the innate and adaptive immune system is a hallmark of TNBS-induced inflammation and is linked to disruption of the intrinsic lymph pump. Recent identification of crosstalk between lymphatic vessel resident immune cells and regulation of lymphatic vessel contractility underscore the importance of the timing of lymphatic dysfunction during tissue inflammation in response to TNBS.

METHODS

To evaluate lymphatic function in TNBS induced inflammation, lymph was collected and flow measured from mesenteric lymphatics. Cellularity and cytokine profile of the lymph was also measured. Histopathology was performed to determine severity of injury and immunofluorescent staining of the mesentery was done to evaluate changes in the population of immune cells that reside near and on gastro-intestinal collecting lymphatics.

RESULTS

Lymph transport fell 24 hours after TNBS administration and began recovering at 72 hours. Significant reduction of lymph flow preceded significant increase in histopathological score and occurred simultaneously with increased myeloperoxidase activity. These changes were preceded by increased MHCII cells surrounding mesenteric lymphatics leading to an altered lymphatic environment that would favor dysfunction.

CONCLUSIONS

Alterations in environmental factors that effect lymphatic function occur before the development of gross GI inflammation. Reduced lymphatic function in TNBS-mediated inflammation is likely an early factor in the development of injury and that recovery of function is associated with resolution of inflammation.