Persistent virus-specific and clonally expanded antibody-secreting cells respond to induced self-antigen in the CNS

The bidirectional relationship of depression and disturbances in B cell homeostasis: Double trouble

Major depressive disorder (MDD) is a recurrent, persistent, and debilitating neuropsychiatric syndrome with an increasing morbidity and mortality, representing the leading cause of disability worldwide. The dysregulation of immune systems (including innate and adaptive immune systems) has been identified as one of the key contributing factors in the progression of MDD. As the main force of the humoral immunity, B cells have an essential role in the defense against infections, antitumor immunity and autoimmune diseases. Several recent studies have suggested an intriguing connection between disturbances in B cell homeostasis and the pathogenesis of MDD, however, the B-cell-dependent mechanism of MDD remains largely unexplored compared to other immune cells. In this review, we provide an overview of how B cell abnormality regulates the progression of MMD and the potential consequence of the disruption of B cell homeostasis in patients with MDD. Abnormalities of B-cell homeostasis not only promote susceptibility to MDD, but also lead to an increased risk of developing infection, malignancy and autoimmune diseases in patients with MDD. A better understanding of the contribution of B cells underlying MDD would provide opportunities for identification of more targeted treatment approaches and might provide an overall therapeutic benefit to improve the long-term outcomes of patients with MDD.

Single cell transcriptomics of cerebrospinal fluid cells from patients with recent-onset narcolepsy

Narcolepsy is a rare cause of hypersomnolence and may be associated or not with cataplexy, i.e. sudden muscle weakness. These forms are designated narcolepsy-type 1 (NT1) and -type 2 (NT2), respectively. Notable characteristics of narcolepsy are that most patients carry the HLA-DQB1*06:02 allele and NT1-patients have strongly decreased levels of hypocretin-1 (synonym orexin-A) in the cerebrospinal fluid (CSF). The pathogenesis of narcolepsy is still not completely understood but the strong HLA-bias and increased frequencies of CD4+ T cells reactive to hypocretin in the peripheral blood suggest autoimmune processes in the hypothalamus. Here we analyzed the transcriptomes of CSF-cells from twelve NT1 and two NT2 patients by single cell RNAseq (scRNAseq). As controls, we used CSF cells from patients with multiple sclerosis, radiologically isolated syndrome, and idiopathic intracranial hypertension. From 27,255 CSF cells, we identified 20 clusters of different cell types and found significant differences in three CD4+ T cell and one monocyte clusters between narcolepsy and multiple sclerosis patients. Over 1000 genes were differentially regulated between patients with NT1 and other diseases. Surprisingly, the most strongly upregulated genes in narcolepsy patients as compared to controls were coding for the genome-encoded MTRNR2L12 and MTRNR2L8 peptides, which are homologous to the mitochondria-encoded HUMANIN peptide that is known playing a role in other neurological diseases including Alzheimer's disease.

B cell phylogenetics in the single cell era

The widespread availability of single-cell RNA sequencing (scRNA-seq) has led to the development of new methods for understanding immune responses. Single-cell transcriptome data can now be paired with B cell receptor (BCR) sequences. However, RNA from BCRs cannot be analyzed like most other genes because BCRs are genetically diverse within individuals. In humans, BCRs are shaped through recombination followed by mutation and selection for antigen binding. As these processes co-occur with cell division, B cells can be studied using phylogenetic trees representing the mutations within a clone. B cell trees can link experimental timepoints, tissues, or cellular subtypes. Here, we review the current state and potential of how B cell phylogenetics can be combined with single-cell data to understand immune responses.

The pathogenesis of multiple sclerosis: a series of unfortunate events

Multiple sclerosis (MS) is characterized by the chronic inflammatory destruction of myelinated axons in the central nervous system. Several ideas have been put forward to clarify the roles of the peripheral immune system and neurodegenerative events in such destruction. Yet, none of the resulting models appears to be consistent with all the experimental evidence. They also do not answer the question of why MS is exclusively seen in humans, how Epstein-Barr virus contributes to its development but does not immediately trigger it, and why optic neuritis is such a frequent early manifestation in MS. Here we describe a scenario for the development of MS that unifies existing experimental evidence as well as answers the above questions. We propose that all manifestations of MS are caused by a series of unfortunate events that usually unfold over a longer period of time after a primary EBV infection and involve periodic weakening of the blood-brain barrier, antibody-mediated CNS disturbances, accumulation of the oligodendrocyte stress protein αB-crystallin and self-sustaining inflammatory damage.