GM-CSF-licensed CD11b+ lung dendritic cells orchestrate Th2 immunity to Blomia tropicalis.

The Blomia tropicalis dust mite is prevalent in tropical and subtropical regions of the world. Although it is a leading cause of asthma, little is known how it induces allergy. Using a novel murine asthma model induced by intranasal exposure to B. tropicalis, we observed that a single intranasal sensitization to B. tropicalis extract induces strong Th2 priming in the lung draining lymph node. Resident CD11b(+) dendritic cells (DCs) preferentially transport Ag from the lung to the draining lymph node and are crucial for the initiation of Th2 CD4(+) T cell responses. As a consequence, mice selectively deficient in CD11b(+) DCs exhibited attenuated Th2 responses and more importantly did not develop any allergic inflammation. Conversely, mice deficient in CD103(+) DCs and CCR2-dependent monocyte-derived DCs exhibited similar allergic inflammation compared with their wild-type counterparts. We also show that CD11b(+) DCs constitutively express higher levels of GM-CSF receptor compared with CD103(+) DCs and are thus selectively licensed by lung epithelial-derived GM-CSF to induce Th2 immunity. Taken together, our study identifies GM-CSF-licensed CD11b(+) lung DCs as a key component for induction of Th2 responses and represents a potential target for therapeutic intervention in allergy.

CD8 T cells regulate allergic contact dermatitis by modulating CCR2-dependent TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells.

Monocytes and their derived cells have critical roles in inflammation and immune defense. However, their function in skin diseases such as allergic contact dermatitis remains poorly defined. Using a model of contact hypersensitivity (CHS) toward 2,4-dinitrochlorobenzene, we show that Ly6C+ CD11b+ monocytic cells participate in the pathophysiology of CHS and their accumulation is regulated by effector CD8 T cells. These Ly6C+ CD11b+ monocytic cells are the primary contributors of tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) and derive from Ly6C(hi)CCR2+ monocytes, as they were absent in non-inflamed skin and accumulate as a consequence of inflammation in a C-C chemokine receptor type 2 (CCR2)-dependent manner. Importantly, CCR2(-/-) mice, or wild-type mice depleted of monocytes via clodronate liposomes, display a marked decrease in TNF-α and iNOS expression accompanied by attenuated skin inflammation. Using transgenic mice and antibody depletion, we show that effector CD8 T cells regulate the accumulation of Ly6C+ CD11b+ monocytic cells through IL-17 and activate them for TNF-α and iNOS through IFN-γ. CD8 T cell-derived IFN-γ was also critical for the accumulation of the major histocompatibility complex II-expressing Ly6C+ CD11b+ subset, which expressed intermediate levels of CD11c and costimulatory molecules. Taken together, our findings provide further insight into the pathophysiology of allergic contact dermatitis by showing that CD8 T cells regulate the inflammatory cascade through TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells.

Neutrophils contribute to inflammatory lymphangiogenesis by increasing VEGF-A bioavailability and secreting VEGF-D.

Lymphangiogenesis is an important physiological response to inflammatory insult, acting to limit inflammation. Macrophages, dendritic cells, and lymphocytes are known to drive lymphangiogenesis. In this study, we show that neutrophils recruited to sites of inflammation can also coordinate lymphangiogenesis. In the absence of B cells, intranodal lymphangiogenesis induced during prolonged inflammation as a consequence of immunization is dependent on the accumulation of neutrophils. When neutrophils are depleted in wild-type mice developing skin inflammation in response to immunization or contact hypersensitization, lymphangiogenesis is decreased and local inflammation is increased. We demonstrate that neutrophils contribute to lymphangiogenesis primarily by modulating vascular endothelial growth factor (VEGF)-A bioavailability and bioactivity and, to a lesser extent, secreting VEGF-D. We further show that neutrophils increased VEGF-A bioavailability and bioactivity via the secretion of matrix metalloproteinases 9 and heparanase. Together, these findings uncover a novel function for neutrophils as organizers of lymphangiogenesis during inflammation.

Expansion of cortical and medullary sinuses restrains lymph node hypertrophy during prolonged inflammation.

During inflammation, accumulation of immune cells in activated lymph nodes (LNs), coupled with a transient shutdown in lymphocyte exit, results in dramatic cellular expansion. Counter-regulatory measures to restrain LN expansion must exist and may include re-establishment of lymphocyte egress to steady-state levels. Indeed, we show in a murine model that egress of lymphocytes from LNs was returned to steady-state levels during prolonged inflammation following initial retention. This restoration in lymphocyte egress was supported by a preferential expansion of cortical and medullary sinuses during late inflammation. Cortical and medullary sinus remodeling during late inflammation was dependent on temporal and spatial changes in vascular endothelial growth factor-A distribution. Specifically, its expression was restricted to the subcapsular space of the LN during early inflammation, whereas its expression was concentrated in the paracortical and medullary regions of the LN at later stages. We next showed that this process was mostly driven by the synergistic cross-talk between fibroblastic reticular cells and interstitial flow. Our data shed new light on the biological significance of LN lymphangiogenesis during prolonged inflammation and further underscore the collaborative roles of stromal cells, immune cells, and interstitial flow in modulating LN plasticity and function.