Summary• Chilling triggers rapid molecular responses that permit the maintenance of plant cell homeostasis and plant adaptation. Recent data showed that nitric oxide (NO) is involved in plant acclimation and tolerance to cold. The participation of NO in the early transduction of the cold signal in Arabidopsis thaliana was investigated.• The production of NO after a short exposure to cold was assessed using the NOsensitive fluorescent probe 4, 5-diamino fluoresceine diacetate and chemiluminescence. Pharmacological and genetic approaches were used to analyze NO sources and NO-mediated changes in cold-regulated gene expression, phosphatidic acid (PtdOH) synthesis and sphingolipid phosphorylation.• NO production was detected after 1-4 h of chilling. It was impaired in the nia1nia2 nitrate reductase mutant. Moreover, NO accumulation was not observed in H7 plants overexpressing the A. thaliana nonsymbiotic hemoglobin Arabidopsis haemoglobin 1 (AHb1). Cold-regulated gene expression was affected in nia1nia2 and H7 plants. The synthesis of PtdOH upon chilling was not modified by NO depletion. By contrast, the formation of phytosphingosine phosphate and ceramide phosphate, two phosphorylated sphingolipids that are transiently synthesized upon chilling, was negatively regulated by NO.• Taken together, these data suggest a new function for NO as an intermediate in gene regulation and lipid-based signaling during cold transduction.

Background Primary Sjögren's syndrome (pSS) is the autoimmune disease associated with the higher risk of developing non-Hodgkin lymphoma. Objective To determine the nature of B cells driving lymphoproliferation in pSS. Methods B cell subsets and function were analyzed in peripheral blood from 66 adult patients with pSS [including 14 patients with B-cell lymphoproliferative disorder (LPD)] and 30 healthy donors, using flow cytometry, calcium mobilization, and gene array analysis. We tested by ELISA the reactivity of recombinant antibodies isolated from single B cells from pSS-LPD. Results We report here the expansion of an unusual CD21-/low B-cell population which correlates with lymphoproliferation in pSS patients. A majority of CD21–/low B cells from pSS patients expressed autoreactive antibodies, which recognized nuclear and cytoplasmic structures. These B cells belonged to the memory compartment because their immunoglobulin genes were mutated. They were unable to induce calcium flux, become activated, or proliferate in response to B-cell receptor and/or CD40 triggering, suggesting that these autoreactive B cells may be anergic. However, CD21–/low B cells from pSS remained responsive to TLR stimulation. Gene array analyses of CD21–/low B cells revealed molecules specifically expressed in these B cells and that are likely to induce their unresponsive stage. Conclusion pSS patients who display high frequencies of autoreactive and unresponsive CD21-/low B cells are susceptible for developing lymphoproliferation. These cells remain in peripheral blood controlled by functional anergy instead of being eliminated, and chronic antigenic stimulation through TLR stimulation may create a favorable environment for breaking tolerance and activating these cells.

Homeostasis of peripheral B cell subsets is disturbed during chronic hepatitis C virus (HCV) infection, leading to the occurrence of autoimmunity and B cell lymphoproliferation. However, mechanisms by which HCV causes lymphoproliferation remain controversial. We report in this article on the elevated number of clonal CD21−/lowIgM+CD27+ marginal zone (MZ)-like B cells, which correlates with autoimmunity and lymphoproliferation in HCV patients. We found an increase in autoreactive BCRs using VH1–69 and VH4–34 genes in CD21−/low MZ B cells. CD21−/low MZ B cells showed impaired calcium-mediated signaling, did not upregulate activation markers, and did not proliferate in response to BCR triggering. CD21−/low MZ B cells also were prone to dying faster than their CD21+ counterparts, suggesting that these B cells were anergic. CD21−/low MZ B cells, in contrast, remained responsive to TLR9 stimulation. Gene array analyses revealed the critical role of Early growth response 2 and Cbl-b in the induction of anergy. Therefore, HCV patients who display high frequencies of unresponsive CD21−/low MZ B cells are more susceptible to developing autoimmunity and/or lymphoproliferation. These cells remain in peripheral blood controlled by functional anergy instead of being eliminated, and chronic antigenic stimulation through TLR stimulation may create a favorable environment for breaking tolerance and activating these cells.