Chronic inflammation, neutrophil activity, and autoreactivity splits long COVID

While immunologic correlates of COVID-19 have been widely reported, their associations with post-acute sequelae of COVID-19 (PASC) remain less clear. Due to the wide array of PASC presentations, understanding if specific disease features associate with discrete immune processes and therapeutic opportunities is important. Here we profile patients in the recovery phase of COVID-19 via proteomics screening and machine learning to find signatures of ongoing antiviral B cell development, immune-mediated fibrosis, and markers of cell death in PASC patients but not in controls with uncomplicated recovery. Plasma and immune cell profiling further allow the stratification of PASC into inflammatory and non-inflammatory types. Inflammatory PASC, identifiable through a refined set of 12 blood markers, displays evidence of ongoing neutrophil activity, B cell memory alterations, and building autoreactivity more than a year post COVID-19. Our work thus helps refine PASC categorization to aid in both therapeutic targeting and epidemiological investigation of PASC.

Normal IgG protects against acute graft-versus-host disease by targeting CD4(+)CD134(+) donor alloreactive T cells

Intravenous immunoglobulin (IVIg) was shown to decrease the severity of acute graft-versus-host disease (aGVHD) in recipients of allogeneic bone marrow transplants. To investigate the mechanisms involved in the protective effect of IVIg, we have used the parent-into-F1 model in which parental lymphocytes are transferred into semi-syngeneic non-irradiated F1 rats. Here we report that IVIg, as well as F(ab')(2) fragments of IVIg, protected (Lewis x Brown-Norway) F1 rats against aGVHD induced by a single injection of Lewis lymphocytes. IVIg was given as five consecutive daily injections, starting on the day preceding that of the transfer of Lewis cells. Protection was associated with a decreased ability of lymphocytes to spontaneously proliferate and to produce NO and IFN-gamma, in the absence of an increased production of IL-10. We further demonstrate that protection was associated with a decrease in CD4(+) T cells bearing the activation marker CD134 in vivo, and with an enhanced apoptosis of activated CD4(+) T cells by IVIg, in vitro. Our observations suggest that the prevention of aGVHD by IVIg in this model is mediated by the induction of apoptosis of activated alloreactive CD4(+)CD134(+) donor T cells. The results further emphasize the role of normal immunoglobulin in modulating alloantigen immune responsiveness.