Limb lymph node response to bone fracture

In previous clinical studies, dilation of afferent lymphatics and enlargement of inguinal lymph nodes (LN) were observed in lymphoscintigrams from patients with persistent posttraumatic edema of lower extremities after fractures and trauma of soft tissues. In this study, changes in rat popliteal and iliac lymph nodes draining lymph from the site of tibial fracture and adjacent soft tissue injury were investigated. The observed parameters were lymph node weight, cell number, phenotype frequency, cell cytokine expression, and reactivity to mitogens. The key observations included: a) increase in the weight and total cell number of the lymph nodes; b) increased autotransformation rate and responsiveness of lymph node cells to mitogen; c) decreased frequency of ED1 macrophages and activated OX8 cytotoxic cells in flow cytometry analysis; d) high expression of OX6 class II-positive, OX7 (stem cells), OX62 (migrating dendritic cells), ED1 (macrophages), and OX12 (B cells) on immunohistochemical sections of LNs with some few HIS48 (granulocytes); e) high expression of NOS3 and TGF beta by lymph node lymphocytes and endothelial cells. In summary, local lymph nodes reacted to internal wounds, such as bone fracture and injury to adjacent tissues, through mobilization of cells from the blood circulation, along with activation of cellular subsets. The molecular mechanism that provides the signal for this reaction remains unknown. The absence of major changes in the frequency of lymph node cell subpopulations indicates that lymph nodes are constitutively prepared for influx of antigens from damaged tissues and react only with increase in cell number and cell activation. The nature of the reaction, including lack of immunization against autoantigens, remains unclear. Further elucidation will require studies on the mechanism of cross-tolerance to self-antigens during wound healing.