Dendritic cells (DC) connect the innate and adaptive arms of the immune system and carry out numerous roles that are significant in the context of viral disease. Their functions include the control of inflammatory responses, the promotion of tolerance, cross-presentation, immune cell recruitment and the production of antiviral cytokines. Based primarily on the available literature that characterizes the behaviour of many DC subsets during Severe acute respiratory syndrome (SARS) and coronavirus disease 2019 (COVID-19), we speculated possible mechanisms through which DC could contribute to COVID-19 immune responses, such as dissemination of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to lymph nodes, mounting dysfunctional inteferon responses and T cell immunity in patients. We highlighted gaps of knowledge in our understanding of DC in COVID-19 pathogenesis and discussed current pre-clinical development of therapies for COVID-19.

Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) have been thoroughly explored in the treatment of various psychiatric disorders and neuropsychiatric symptoms. However, whether combining rTMS and tDCS can safely and effectively treat psychiatric conditions remains unknown. In this systematic review, we seek to summarize all existing studies that have combined rTMS and tDCS to remedy psychiatric disorders and symptoms. We searched four databases in addition to grey literature to identify relevant studies. All abstracts and manuscripts were independently reviewed by two reviewers. For inclusion, studies necessarily consisted of those who received both rTMS and tDCS for a psychiatric condition or symptom. Fourteen studies were reviewed, which had relevance to unipolar depression (five), bipolar disorder (two), obsessive-compulsive disorder (two), Alzheimer's Disease (one), chronic insomnia (two), depressive and anxiety symptoms (one) and stress (one). In three RCTs on unipolar depression, the group receiving both rTMS and tDCS experienced significant reductions in mean Hamilton Depression Rating Scale (HDRS) scores (by 18.22, 16.59 and 20.04) as well as response rates (83.33 % and 91.7 %) and remission rates (83.3 %) - all of which were generally superior compared to treatment with rTMS or tDCS alone. For chronic insomnia, one RCT noted greater improvements in sleep quality/efficiency and depressive symptoms compared to monotherapy. The type and frequency of side effects were comparable to monotherapy, and no significant adverse events were reported. The existing evidence suggests that combining rTMS and tDCS alone yields greater symptomatic benefit for unipolar depression compared to either treatment alone. Further studies involving additional protocols and disorders could elucidate the utility of combined treatment.