Tapping out a mechanical code for T cell triggering

Membraneless organelles restructured and built by pandemic viruses: HIV-1 and SARS-CoV-2

Viruses hijack host functions to invade their target cells and spread to new cells. Specifically, viruses learned to usurp liquid‒liquid phase separation (LLPS), a newly exploited mechanism, used by the cell to concentrate enzymes to accelerate and confine a wide variety of cellular processes. LLPS gives rise to actual membraneless organelles (MLOs), which do not only increase reaction rates but also act as a filter to select molecules to be retained or to be excluded from the liquid droplet. This is exactly what seems to happen with the condensation of SARS-CoV-2 nucleocapsid protein to favor the packaging of intact viral genomes, excluding viral subgenomic or host cellular RNAs. Another older pandemic virus, HIV-1, also takes advantage of LLPS in the host cell during the viral cycle. Recent discoveries highlighted that HIV-1 RNA genome condensates in nuclear MLOs accompanied by specific host and viral proteins, breaking the dogma of retroviruses that limited viral synthesis exclusively to the cytoplasmic compartment. Intriguing fundamental properties of viral/host LLPS remain still unclear. Future studies will contribute to deeply understanding the role of pathogen-induced MLOs in the epidemic invasion of pandemic viruses.

Imaging: Gear up for mechano-immunology

Immune cells including B and T lymphocytes have a remarkable ability to sense the physical perturbations through their surface expressed receptors. At the advent of modern imaging technologies paired with biophysical methods, we have gained the understanding of mechanical forces exerted by immune cells to perform their functions. This review will go over the imaging techniques already being used to study mechanical forces in immune cells. We will also discuss the dire need for new modern technologies for future work.

Matrine inhibits itching by lowering the activity of calcium channel

Sophorae Flavescentis Radix (SFR) is a medicinal herb with many functions that are involved in anti-inflammation, antinociception, and anticancer. SFR is also used to treat a variety of itching diseases. Matrine (MT) is one of the main constituents in SFR and also has the effect of relieving itching, but the antipruritic mechanism is still unclear. Here, we investigated the effect of MT on anti-pruritus. In acute and chronic itch models, MT significantly inhibited the scratching behavior not only in acute itching induced by histamine (His), chloroquine (CQ) and compound 48/80 with a dose-depended manner, but also in the chronic pruritus models of atopic dermatitis (AD) and acetone-ether-water (AEW) in mice. Furthermore, MT could be detected in the blood after intraperitoneal injection (i.p.) and subcutaneous injection (s.c.). Finally, electrophysiological and calcium imaging results showed that MT inhibited the excitatory synaptic transmission from dorsal root ganglion (DRG) to the dorsal horn of the spinal cord by suppressing the presynaptic N-type calcium channel. Taken together, we believe that MT is a novel drug candidate in treating pruritus diseases, especially for histamine-independent and chronic pruritus, which might be attributed to inhibition of the presynaptic N-type calcium channel.

PI(4,5)P2 determines the threshold of mechanical force-induced B cell activation

B lymphocytes use B cell receptors (BCRs) to sense the chemical and physical features of antigens. The activation of isotype-switched IgG-BCR by mechanical force exhibits a distinct sensitivity and threshold in comparison with IgM-BCR. However, molecular mechanisms governing these differences remain to be identified. In this study, we report that the low threshold of IgG-BCR activation by mechanical force is highly dependent on tethering of the cytoplasmic tail of the IgG-BCR heavy chain (IgG-tail) to the plasma membrane. Mechanistically, we show that the positively charged residues in the IgG-tail play a crucial role by highly enriching phosphatidylinositol (4,5)-biphosphate (PI(4,5)P2) into the membrane microdomains of IgG-BCRs. Indeed, manipulating the amounts of PI(4,5)P2 within IgG-BCR membrane microdomains significantly altered the threshold and sensitivity of IgG-BCR activation. Our results reveal a lipid-dependent mechanism for determining the threshold of IgG-BCR activation by mechanical force.