Lymph node fibroblastic reticular cells directly present peripheral tissue antigen under steady-state and inflammatory conditions.

Lymph node stromal cells (LNSCs) can induce potent, antigen-specific T cell tolerance under steady-state conditions. Although expression of various peripheral tissue-restricted antigens (PTAs) and presentation to naive CD8+ T cells has been demonstrated, the stromal subsets responsible have not been identified. We report that fibroblastic reticular cells (FRCs), which reside in the T cell zone of the LN, ectopically express and directly present a model PTA to naive T cells, inducing their proliferation. However, we found that no single LNSC subset was responsible for PTA expression; rather, each subset had its own characteristic antigen display. Studies to date have concentrated on PTA presentation under steady-state conditions; however, because LNs are frequently inflammatory sites, we assessed whether inflammation altered stromal cell-T cell interactions. Strikingly, FRCs showed reduced stimulation of T cells after Toll-like receptor 3 ligation. We also characterize an LNSC subset expressing the highest levels of autoimmune regulator, which responds potently to bystander inflammation by up-regulating PTA expression. Collectively, these data show that diverse stromal cell types have evolved to constitutively express PTAs, and that exposure to viral products alters the interaction between T cells and LNSCs.

Integrin-independent movement of immune cells.

Cell motility requires the temporal and spatial coordination of the actin cytoskeleton with cell-matrix adhesions. Since their discovery more than 20 years ago, integrins have been at the center of cell-matrix adhesion research. Integrin-mediated adhesions link the actin network to the extracellular matrix and are commonly observed as cells migrate across rigid two-dimensional substrates. However, as more cell motility studies are being conducted in three-dimensional (3D) culture systems and in vivo, the role of integrins has become less clear. Recent work has shown that leukocyte migration in 3D contexts can be integrin-independent and that alternative mechanisms of cell adhesion are employed.

ROCK- and myosin-dependent matrix deformation enables protease-independent tumor-cell invasion in vivo.

Tumor cells invading three-dimensional matrices need to remodel the extracellular matrix (ECM) in their path. Many studies have focused on the role of extracellular proteases; however, cells with amoeboid or rounded morphologies are able to invade even when these enzymes are inhibited. Here, we describe the mechanism by which cells move through a dense ECM without proteolysis. Amoeboid tumor cells generate sufficient actomyosin force to deform collagen fibers and are able to push through the ECM. Force generation is elevated in metastatic MTLn3E cells, and this correlates with increased invasion and altered myosin light chain (MLC) organization. In metastatic cells, MLC is organized perpendicularly to the direction of movement behind the invading edge. Both the organization of MLC and force generation are dependent upon ROCK function. We demonstrate that ROCK regulates the phosphorylation of MLC just behind the invading margin of the cell. Imaging of live tumors shows that MLC is organized in a similar ROCK-dependent fashion in vivo and that inhibition of ROCK but not matrix-metalloproteases reduces cancer cell motility in vivo.