Platelets regulate lymphatic vascular development through CLEC-2-SLP-76 signaling.

Although platelets appear by embryonic day 10.5 in the developing mouse, an embryonic role for these cells has not been identified. The SYK-SLP-76 signaling pathway is required in blood cells to regulate embryonic blood-lymphatic vascular separation, but the cell type and molecular mechanism underlying this regulatory pathway are not known. In the present study we demonstrate that platelets regulate lymphatic vascular development by directly interacting with lymphatic endothelial cells through C-type lectin-like receptor 2 (CLEC-2) receptors. PODOPLANIN (PDPN), a transmembrane protein expressed on the surface of lymphatic endothelial cells, is required in nonhematopoietic cells for blood-lymphatic separation. Genetic loss of the PDPN receptor CLEC-2 ablates PDPN binding by platelets and confers embryonic lymphatic vascular defects like those seen in animals lacking PDPN or SLP-76. Platelet factor 4-Cre-mediated deletion of Slp-76 is sufficient to confer lymphatic vascular defects, identifying platelets as the cell type in which SLP-76 signaling is required to regulate lymphatic vascular development. Consistent with these genetic findings, we observe SLP-76-dependent platelet aggregate formation on the surface of lymphatic endothelial cells in vivo and ex vivo. These studies identify a nonhemostatic pathway in which platelet CLEC-2 receptors bind lymphatic endothelial PDPN and activate SLP-76 signaling to regulate embryonic vascular development.

Early versus late surgical management of complicated appendicitis in children: A statewide database analysis with one-year follow-up.

BACKGROUND: Complicated appendicitis is common in children, yet the timing of surgical management remains controversial. Some support initial antibiotics with delayed operation whereas others support immediate operation. While a few randomized trials have evaluated this question, they have been small, single-center trials with limited follow-up. We present a database analysis of outcomes in early versus late surgical management of complicated appendicitis with one-year follow-up. METHODS: We conducted a retrospective review of children with complicated appendicitis presenting between 2000 and 2013, utilizing a New York State database. We compare children undergoing later versus early appendectomy with a primary outcome measure of any complication within one year as determined from ICD-9 codes. RESULTS: 8840 children were included in the analysis, 7708 of whom underwent early appendectomy. Patients with late appendectomy were significantly more likely to have at least one complication when compared to those undergoing early appendectomy (34.6% vs 26.7%, p<0.01). CONCLUSIONS: We present the first population-level study evaluating early versus late appendectomy in children with complicated appendicitis with a one-year follow-up period. Children undergoing late appendectomy were more likely to have a complication than those undergoing early appendectomy. These data corroborated previous studies supporting early operative management. LEVEL OF EVIDENCE: This study provides level III evidence of a treatment study.

Maternal alloantibodies induce a postnatal immune response that limits engraftment following in utero hematopoietic cell transplantation in mice.

The lack of fetal immune responses to foreign antigens, i.e., fetal immunologic tolerance, is the most compelling rationale for prenatal stem cell and gene therapy. However, the frequency of engraftment following in utero hematopoietic cell transplantation (IUHCT) in the murine model is reduced in allogeneic, compared with congenic, recipients. This observation supports the existence of an immune barrier to fetal transplantation and challenges the classic assumptions of fetal tolerance. Here, we present evidence that supports the presence of an adaptive immune response in murine recipients of IUHCT that failed to maintain engraftment. However, when IUHCT recipients were fostered by surrogate mothers, they all maintained long-term chimerism. Furthermore, we have demonstrated that the cells responsible for rejection of the graft were recipient in origin. Our observations suggest a mechanism by which IUHCT-dependent sensitization of the maternal immune system and the subsequent transmission of maternal alloantibodies to pups through breast milk induces a postnatal adaptive immune response in the recipient, which, in turn, results in the ablation of engraftment after IUHCT. Finally, we showed that non-fostered pups that maintained their chimerism had higher levels of Tregs as well as a more suppressive Treg phenotype than their non-chimeric, non-fostered siblings. This study resolves the apparent contradiction of induction of an adaptive immune response in the pre-immune fetus and confirms the potential of actively acquired tolerance to facilitate prenatal therapeutic applications.