Volume Articles

The low down on sphingosine-1-phosphate lyase as a regulator of thymic egress

Julie D. Saba*

After undergoing positive and negative selection in the thymus, surviving mature T cells egress from the thymic parenchyma and enter the bloodstream to participate in adaptive immunity. Thymic egress requires signals mediated by sphingosine-1-phosphate (S1P), a bioactive lipid that serves as the ligand for a family of G protein-coupled receptors (S1P1-5) expressed on many cell types, including T cells. In the final stage of their development, T cells upregulate S1P1 expression on the cell surface, which enables them to recognize and respond to a chemotactic S1P gradient that lures them into the bloodstream. The gradient is generated by an S1P source close to the site of egress combined with an S1P sink generated by the actions of S1P catabolic enzymes including S1P lyase (SPL), the only enzyme that irreversibly degrades S1P. The requisite contribution of SPL to thymic egress is demonstrated by the profound lymphopenia observed in SPL knockout (KO) mice and wild type mice treated with SPL inhibitors. SPL is robustly expressed in thymic epithelial cells (TECs), which make up the stromal reticular network of the thymus. However, TEC SPL was recently found to be dispensable for thymic egress. In contrast, deletion of SPL in dendritic cells (DCs) — which represent only a small percent of thymic stroma — disrupts the S1P gradient and blocks thymic egress. These recent observations identify DCs as homeostatic regulators of thymic export through the actions of SPL, thereby adding one more piece to the complex puzzle of how S1P signaling contributes to the regulation of T cell trafficking.

Ficolin-2 triggers antitumor and anti-pathogen effects by activating antigen presenting cells and CD8+T cells

Quanquan Ding, Min Liu, Xiao-Lian Zhang*

New dimensions in intravital multi-photon imaging of immune reactions

Asylkhan Rakhymzhan^1*, Randall L. Lindquist^1*, Anja E. Hauser^1,2#, Raluca Niesner^1#

In the last two decades intravital multi-photon imaging has become a central tool to investigate cellular and molecular dynamics of immune reactions in vivo. Currently, challenges in exploiting the full power of this technology include limitations on the number of simultaneously detectable parameters as well as in expanding the acquisition in time and space. Here we discuss technological advancements developed in order to overcome these challenges and focus on the example of germinal center reactions as multi-parametric immunological processes evolving over a time course of days and weeks.

RIC-3, a potential target for regulating cholinergic signaling and inflammation

Millet Treinin*

The nicotinic acetylcholine receptor (nAChR) gene family encodes for subunits of acetylcholine gated ion channels. These receptors are expressed widely and have many functions including anti-inflammatory effects mediated by the α7 nAChR, as part of the cholinergic anti-inflammatory pathway, in immune cells, microglia and astrocytes. Maturation of α7 nAChRs into functional ligand-gated ion channels in the plasma membrane is a complex process likely to require the RIC-3 protein. This endoplasmic reticulum resident chaperone affects maturation of multiple nAChRs, but its interaction with these receptors and its effects on their maturation differ for different nAChRs. Moreover, these interactions and effects are regulated by multiple mechanisms. Genetic analysis has implicated RIC-3 in the neuroinflammatory disease Multiple Sclerosis (MS), and in the neurodegenerative Parkinson's disease (PD). Neuroinflammation contributes to the progression of neurodegenerative diseases including PD. This information combines to suggest that RIC-3 may contribute to progression of both MS and PD via its effects on the α7 nAChR and the cholinergic anti-inflammatory pathway. Furthermore, we suggest that mechanisms regulating RIC-3 expression and activity may have a role in controlling inflammation.

Sneaking ligands inhibiting NF-kappaB activation selectively in endothelial cells improve experimental arthritides

Bettina Sehnert^1*, Harald Burkhardt², Stefan Dübel³, Reinhard E. Voll¹

The activation of intracellular signaling pathways such as the classical nuclear factor kappaB (NF-kappaB) pathway is related to the pathogenesis of several inflammatory autoimmune diseases including rheumatoid arthritis (RA). To clarify the role of disease-relevant cell-types and signaling molecules in vitro or in vivo, it is necessary to target them selectively without disturbing the homeostasis of the immune system. We developed sneaking ligand fusion proteins (SLFPs) for cell-type specific modulation of signaling pathways. We designed the first SLFPs to inhibit the activation of NF-kappaB, a key regulator of inflammation, solely in the activated endothelium. Our “sneaking ligand” NF-kappaB inhibitor (named SLC1) inhibits NF-kappaB activation specifically in E-selectin expressing cells in vitro and in mouse models of arthritis indicating the importance of NF-kappaB in the activated endothelium. Clinical signs of arthritis were ameliorated by SLC1 treatment. We conclude that the SLFP architecture consisting of easily exchangeable domains represents an attractive approach to utilize other disease-relevant biological targets both on the cell surface and intracellularly. By relying on two independent disease specific targets, SLFPs may increase the therapeutic efficacy and reduce adverse effects.

Commentary to "A Case of Recombinant Coxsackievirus A2 Infection with Neurological Complications in Taiwan"

Kao-Pin Hwang^1*, Ting-Yu Yen¹