Monocyte-derived dendritic cells perform hemophagocytosis to fine-tune excessive immune responses

Because immune responses simultaneously defend and injure the host, the immune system must be finely regulated to ensure the host's survival. Here, we have shown that when injected with high Toll-like receptor ligand doses or infected with lymphocytic choriomeningitis virus (LCMV) clone 13, which has a high viral turnover, inflammatory monocyte-derived dendritic cells (Mo-DCs) engulfed apoptotic erythroid cells. In this process, called hemophagocytosis, phosphatidylserine (PS) served as an "eat-me" signal. Type I interferons were necessary for both PS exposure on erythroid cells and the expression of PS receptors in the Mo-DCs. Importantly, hemophagocytosis was required for interleukin-10 (IL-10) production from Mo-DCs. Blocking hemophagocytosis or Mo-DC-derived IL-10 significantly increased cytotoxic T cell lymphocyte activity, tissue damage, and mortality in virus-infected hosts, suggesting that hemophagocytosis moderates immune responses to ensure the host's survival in vivo. This sheds light on the physiological relevance of hemophagocytosis in severe inflammatory and infectious diseases.

A platform to parallelize planar surfaces and control their spatial separation with nanometer resolution

Parallelizing planar surfaces and manipulating them into close proximity with spatial separation of nanoscale dimensions is critical for probing phenomena such as near-field radiative heat transport and Casimir forces. Here, we report on a novel platform, with an integrated reflected light microscope, that is capable of parallelizing two planar surfaces such that the angular deviation is <6 μrad, while simultaneously allowing control of the gap from 15 μm down to contact with ∼0.15 nm resolution. The capabilities of this platform were verified by using two custom-fabricated micro-devices with planar surfaces, 60 × 60 μm(2) each, whose flatness and surface roughness were experimentally quantified. We first parallelized the two micro-devices by using the developed platform in conjunction with a simple optical approach that relies on the shallow depth of field (∼2 μm) of a long working distance microscope objective. Subsequently, we experimentally tested the parallelism achieved via the optical alignment procedure by taking advantage of electrodes integrated into the micro-devices. Our measurements unambiguously show that the simple depth-of-field based optical approach enables parallelization such that the angular deviation between the two surfaces is within ∼500 μrad. This ensures that the separation between any two corresponding points on the parallel surfaces deviate by ∼30 nm or less from the expected value. Further, we show that improved parallelization can be achieved using the integrated micro-electrodes which enable surface roughness limited parallelization with deviations of ∼5 nm from parallelism.