Possible role for cell-surface carbohydrate-binding molecules in lymphocyte recirculation.

We are investigating the hypothesis that carbohydrate-binding molecules on the cell surface are involved in the recirculation of lymphocytes from the bloodstream into lymphoid organs. This phenomenon requires the specific attachment of circulating lymphocytes to the endothelial cells of postcapillary venules. Using an in vitro assay to measure the adhesive interaction between lymphocytes and postcapillary venules, we have found that L-fucose, D mannose, and the L-fucose-rich, sulfated polysaccharide fucoidin specifically inhibit this binding interaction. L-fucose shows stereo-selective inhibitory activity at concentrations greater than 18 mM while fucoidin produces 50% inhibition at approximately 1-5 X 10(-8) M. Fucoidin appears to interact with the lymphocyte, and not the postcapillary venule, to inhibit binding. These data suggest that cell surface carbohydrates (fucoselike) and carbohydrate-binding molecules (cell surface lectins) may contribute to the specific attachment of lymphocytes to postcapillary venules

Phosphomannosyl receptors may participate in the adhesive interaction between lymphocytes and high endothelial venules.

Normal and malignant lymphocytes can migrate from the bloodstream into lymph nodes and Peyer's patches. This process helps distribute normal lymphocytes throughout the lymphoid system and may provide a portal of entry for circulating malignant cells. An adhesive interaction between lymphocytes and the endothelium of postcapillary venules is the first step in the migratory process. We have recently shown that the simple sugars L-fucose and D-mannose, and an L-fucose-rich polysaccharide (fucoidin), can inhibit this adhesive interaction in vitro. We now report that mannose-6-phosphate, the structurally related sugar fructose-1-phosphate, and a phosphomannan, core polysaccharide from the yeast Hansenula holstii (PPME) are also potent inhibitors. Inhibitory activity was assessed by incubating freshly prepared suspensions of lymphocytes, containing the various additives, over air-dried, frozen sections of syngeneic lymph nodes at 7-10 degrees C. Sections were then evaluated in the light microscope for the binding of lymphocytes to postcapillary venules. Mannose-6-phosphate and fructose-1-phosphate were potent inhibitors of lymphocyte attachment (one-half maximal inhibition at 2-3 mM). Mannose-1-phosphate and fructose-6-phosphate had slight inhibitory activity, while glucose-1-phosphate, glucose-6-phosphate, galactose-1-phosphate, and galactose-6-phosphate had no significant activity (at 10 mM). In addition, the phosphomannan core polysaccharide was a potent inhibitor (one-half maximal inhibition at 10-20 micrograms/ml); dephosphorylation with alkaline phosphatase resulted in loss of its inhibitory activity. Preincubation of the lymphocytes, but not the lymph node frozen sections, with PPME resulted in persistent inhibition of binding. Neither the monosaccharides nor the polysaccharide suppressed protein synthesis nor decreased the viability of the lymphocytes. Furthermore, inhibitory activity did not correlate with an increase in negative charge on the lymphocyte surface (as measured by cellular electrophoresis). These data suggest that a carbohydrate-binding molecule on the lymphocyte surface, with specificity for mannose-phosphates and structurally related carbohydrates, may be involved in the adhesive interaction mediating lymphocyte recirculation

The Role of Interferon-g in the Determination of Central Nervous System Damage in Experimental Autoimmune Encephalomyelitis.

In multiple Sclerosis (MS), a multifocal inflammatory demyelinating disease of the central nervous system (CNS), lesion distribution is variable between patients resulting in distinct patterns of disease progression and clinical deficits. The mechanisms regulating immune cell migration to and subsequent lesion development in different areas of the CNS are not well understood. Experimental Autoimmune Encephalomyelits (EAE), a critical model in developing effective MS therapies, can also be used to examine mechanisms driving lesion localization. In the adoptive transfer EAE model,myelin-specific CD4+ T cell transfer into wild type (WT) mice results in an ascending paralysis due to inflammation in the spinal cord (SC) (conventional EAE), while transfer of these same T cells into mice lacking the interferon-g receptor (IFNgR) results in balance deficits due to inflammation in the brainstem (BS) (atypical EAE). The reciprocal transfer of IFNg KO myelin-specific T cells into WT mice results predominantly in atypical EAE. In addition to deficiencies in IFN signaling, increased IL-17 signaling has also been shown to promote brain inflammation and atypical EAE pathogenesis. However, the mechanisms by which these cytokines promote distinct lesion localization are incompletely characterized. IFNg and IL-17 play reciprocal roles in the recruitment of neutrophils to sites of inflammation. The absence of IFNg or increased IL-17 signaling promote neutrophil infiltration in multiple infection and autoimmune models of disease. Some early studies examined neutrophil infiltration in EAE but none have examined their absolute requirement in atypical EAE. Using adoptive transfer models of EAE, we show that atypical EAE is driven by CXCR2-mediated recruitment of neutrophils to the brainstem, whereas conventional EAE is driven by CCR2-mediated recruitment of monocytes to the spinal cord. We also find that IFNg signaling suppresses atypical EAE by directly inhibiting CXCL2-dependent neutrophil recruitment axis. IFNg directly inhibits CXCL2 production by monocyte and microglia in the BS during EAE. Additionally, IFNg suppresses neutrophil production of CXCL2 in response to CXCR2 binding by directly inhibiting expression of the CXCR2 receptor on neutrophils in the CNS. Overall, these studies identify a distinct CXCR2-dependent recruitment pathway in CNS autoimmunity that is not currently targeted by current disease modifying therapies.PHDImmunologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135769/1/jsto_1.pd

Thematic Analysis of Third-Year Medical Student Reflections on Social Determinants of Health During Their Pediatric Clerkship: Emergent Themes and Topic Interconnectedness

Background. Social determinants of health (SDOH), as defined by the World Health Organization, are the “non-medical factors that influence health outcomes… the conditions in which people are born, grow, work, live, and age, and the wider set of forces and systems shaping the conditions of daily life.” Studies have estimated that SDOH account for 30-55% of health outcomes. Understanding the impact of SDOH can be integrated into medical education in different formats, here we explore student reflections. Methods. In the 2021-2022 academic year, third-year medical students at a midwestern medical school submitted discussion board reflections on their experiences with SDOH during their 8-week pediatric clerkship. We analyzed de-identified posts to look for emergent themes that showcase the experiences and perceptions of medical students as they care for patients and learn about the socio-environmental factors in the community. Initial coding was built on a preliminary codebook drafted based on the medical school’s SDOH curriculum. Utilizing a grounded theory approach, we added new codes as novel topics and themes emerged. We then examined the relationships between the codes and SDOH categories outlined in the US Department of Health and Human Services Healthy People 2030 objectives. Results. Ninety-seven student discussion posts were analyzed. Our preliminary results demonstrate the two most common themes, social support and communication, together represented approximately 50% of all student responses. With the addition of the next two most frequently discussed topics, healthcare access and diet/nutrition, this set of themes comprises over 75% of student responses. Student responses also demonstrated the interconnectedness of SDOH categories through frequent overlap of categories during coding and analysis. Conclusion. Our study demonstrates the most common SDOH themes students identified during the pediatric clerkship involve social support, communication, access to care, and diet/nutrition. We found a multifactorial, connected nature of those themes as they impact patient health. This study validates the need for explicit education on SDOH topics during medical school so that future physicians are well-equipped to intervene or accommodate these factors throughout their careers. Future directions include comparing our results to preexisting social and educational frameworks and future cohort comparisons as curriculum evolves.https://digitalcommons.unmc.edu/chri_forum/1065/thumbnail.jp

Editorial: Mitochondria as a hub in cellular signaling

Editorial on the Research Topic Mitochondria as a hub in cellular signalin

Discovery of a potent nanoparticle P‐selectin antagonist with anti‐inflammatory effects in allergic airway disease

The severity of allergic asthma is dependent, in part, on the intensity of peribronchial inflammation. P‐selectin is known to play a role in the development of allergen‐induced peribronchial inflammation and airway hyperreactivity. Selective inhibitors of P‐selectin‐ mediated leukocyte endothelial‐cell interactions may therefore attenuate the inflammatory processes associated with allergic airway disease. Novel P‐selectin inhibitors were created using a polyvalent polymer nanoparticle capable of displaying multiple synthetic, low molecular weight ligands. By assembling a particle that presents an array of groups, which as monomers interact with only low affinity, we created a construct that binds extremely efficiently to P‐ selectin. The ligands acted as mimetics of the key binding elements responsible for the high‐ avidity adhesion of P‐selectin to the physiologic ligand, PSGL‐1. The inhibitors were initially evaluated using an in vitro shear assay system in which interactions between circulating cells and P‐selectin‐coated capillary tubes were measured. The nanoparticles were shown to preferentially bind to selectins expressed on activated endothelial cells. We subsequently demonstrated that nanoparticles displaying P‐selectin blocking arrays were functionally active in vivo, significantly reducing allergen‐induced airway hyperreactivity and peribronchial eosinophilic inflammation in a murine model of asthma.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154265/1/fsb2fj030166fje-sup-0001.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154265/2/fsb2fj030166fje.pd

Molecular mapping of functional domains of the leukocyte receptor for endothelium, LAM-1

The human lymphocyte homing receptor LAM-1, like its murine counterpart MEL-14, functions as a mammalian lectin, and mediates the binding of leukocytes to specialized high endothelial cells in lymphoid organs (HEV). LAM-1 is a member of a new family of cell adhesion molecules, termed selectins or LEC-CAMs, which also includes ELAM-1 and PAD-GEM (GMP-140/CD62). To localize the regions of LAM-1 that are involved in cell adhesion, we developed chimeric selectins, in which various domains of PAD-GEM were substituted into LAM-1, and used these chimeric proteins to define the domain requirements for carbohydrate binding, and to localize the regions recognized by several mAb which inhibit the adhesion of lymphocytes to lymph node HEV. The binding of PPME or fucoidin, soluble complex carbohydrates that specifically define the lectin activity of LAM-1 and MEL-14, required only the lectin domain of LAM-1. The LAM1-1, LAM1-3, and LAM1-6 mAb each strongly inhibit the binding of lymphocytes to HEV in the in vitro frozen section assay, and defined three independent epitopes on LAM-1. Blocking of PPME or fucoidin binding by LAM1-3 indicated that this site is identical, or in close proximity, to the carbohydrate binding site, and analysis of the binding of LAM1-3 to chimeric selectins showed that the epitope detected by LAM1-3 is located within the lectin domain. Although the LAM1-6 epitope is also located in the lectin domain, LAM1-6 did not affect the binding of PPME or fucoidin. The LAM1-1 epitope was located in, or required, the EGF domain, and, importantly, binding of LAM1-1 significantly enhanced the binding of both PPME and fucoidin. These results suggest that adhesion mediated by LAM-1 may involve cooperativity between functionally and spatially distinct sites, and support previous data suggesting a role for the EGF domain of LAM-1 in lymphocyte adhesion to HEV