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SARS-CoV-2 is the cause of an ongoing pandemic that has infected over 36 million and killed over 1 million people. Informed implementation of government public health policies depends on accurate data on SARS-CoV-2 immunity at population scale. We hypothesized that detection of SARS-CoV-2 salivary antibodies could serve as a non-invasive alternative to serological testing for monitoring of SARS-CoV-2 infection and seropositivity at population scale. We developed a multiplex SARS-CoV-2 antibody immunoassay based on Luminex technology that comprised 12 CoV antigens, mostly derived from SARS-CoV-2 nucleocapsid (N) and spike (S). Saliva and sera collected from confirmed COVID-19 cases and from the pre-COVID-19 era were tested for IgG, IgA and IgM to the antigen panel. Matched saliva and serum IgG responses (n=28) were significantly correlated. The salivary anti-N IgG response resulted in highest sensitivity (100%), exhibiting a positive response in 24/24 RT-PCR-confirmed COVID-19 cases sampled at >14 days post-symptom onset (DPSO), whereas the salivary anti-receptor binding domain (RBD) IgG response yielded 100% specificity. Temporal kinetics of IgG in saliva were consistent with those observed in blood and indicated that most individuals seroconvert around 10 DPSO. Algorithms employing a combination of the IgG response to N and S antigens result in high diagnostic accuracy (100%) as early as 10 DPSO. These results support the use of saliva-based antibody testing as a non-invasive and scalable alternative to blood-based antibody testing.

Mouse small intestine intraepithelial lymphocytes (IEL) that express αβTCR and CD8αα homodimers are an enigmatic T cell subset, as their specificity and in vivo function remain to be defined. To gain insight into the nature of these cells, we performed global gene expression profiling using microarray analysis combined with real-time quantitative PCR and flow cytometry. Using these methods, TCRαβ+CD8αα IEL were compared with their TCRαβ+CD8β+ and TCRγδ+ counterparts. Interestingly, TCRαβ+CD8αα IEL were found to preferentially express genes that would be expected to down-modulate their reactivity. They have a unique expression pattern of members of the Ly49 family of NK receptors and tend to express inhibitory receptors, along with some activating receptors. The signaling machinery of both TCRαβ+CD8αα and TCRγδ+ IEL is constructed differently than other IEL and peripheral T cells, as evidenced by their low-level expression of the linker for activation of T cells and high expression of the non-T cell activation linker, which suppresses T cell activation. The TCRαβ+CD8αα IEL subset also has increased expression of genes that could be involved in immune regulation, including TGF-β3 and lymphocyte activation gene-3. Collectively, these data underscore the fact that, while TCRαβ+CD8αα IEL resemble TCRγδ+ IEL, they are a unique population of cells with regulated Ag reactivity that could have regulatory function.

No abstract

Non-invasive SARS-CoV-2 antibody testing is urgently needed to estimate the incidence and prevalence of SARS-CoV-2 infection at the general population level. Precise knowledge of population immunity could allow government bodies to make informed decisions about how and when to relax stay-at-home directives and to reopen the economy. We hypothesized that salivary antibodies to SARS-CoV-2 could serve as a non-invasive alternative to serological testing for widespread monitoring of SARS-CoV-2 infection throughout the population. We developed a multiplex SARS-CoV-2 antibody immunoassay based on Luminex technology and tested 167 saliva and 324 serum samples, including 134 and 118 negative saliva and serum samples, respectively, collected before the COVID-19 pandemic, and 33 saliva and 206 serum samples from participants with RT-PCR-confirmed SARS-CoV-2 infection. We evaluated the correlation of results obtained in saliva vs. serum and determined the sensitivity and specificity for each diagnostic media, stratified by antibody isotype, for detection of SARS-CoV-2 infection based on COVID-19 case designation for all specimens. Matched serum and saliva SARS-CoV-2 antigen-specific IgG responses were significantly correlated. Within the 10-plex SARS-CoV-2 panel, the salivary anti-nucleocapsid (N) protein IgG response resulted in the highest sensitivity for detecting prior SARS-CoV-2 infection (100% sensitivity at ≥10 days post-SARS-CoV-2 symptom onset). The salivary anti-receptor binding domain (RBD) IgG response resulted in 100% specificity. Among individuals with SARS-CoV-2 infection confirmed with RT-PCR, the temporal kinetics of IgG, IgA, and IgM in saliva were consistent with those observed in serum. SARS-CoV-2 appears to trigger a humoral immune response resulting in the almost simultaneous rise of IgG, IgM and IgA levels both in serum and in saliva, mirroring responses consistent with the stimulation of existing, cross-reactive B cells. SARS-CoV-2 antibody testing in saliva can play a critically important role in large-scale 'sero'-surveillance to address key public health priorities and guide policy and decision-making for COVID-19.

LIGHT is a member of the TNF cytokine superfamily that signals through the lymphotoxin (LT)β receptor and the herpesvirus entry mediator. LIGHT may function as a costimulatory factor for the activation of lymphoid cells and as a deterrent to infection by herpesvirus, which may provide significant selective pressure shaping the evolution of LIGHT. Here, we define the molecular genetics of the human LIGHT locus, revealing its close linkage to the TNF superfamily members CD27 ligand and 4-1BB ligand, and the third complement protein (C3), which positions LIGHT within the MHC paralog on chromosome 19p13.3. An alternately spliced isoform of LIGHT mRNA that encodes a transmembrane-deleted form is detected in activated T cells and gives rise to a nonglycosylated protein that resides in the cytosol. Furthermore, membrane LIGHT is shed from the cell surface of human 293 T cells. These studies reveal new mechanisms involved in regulating the physical forms and cellular compartmentalization of LIGHT that may contribute to the regulation and biological function of this cytokine.

The TNF superfamily of cytokines play an important role in T cell activation and inflammation. Sustained expression of lymphotoxin-like inducible protein that competes with glycoprotein D for binding herpesvirus entry mediator on T cells (LIGHT) (TNFSF14) causes a pathological intestinal inflammation when constitutively expressed by mouse T cells. In this study, we characterized LIGHT expression on activated human T cell subsets in vitro and demonstrated a direct proinflammatory effect on regulation of IFN-γ. LIGHT was induced in memory CD45RO CD4+ T cells and by IFN-γ-producing CD4+ T cells. Kinetic analysis indicated rapid induction of LIGHT by human lamina propria T cells, reaching maximal levels by 2–6 h, whereas peripheral blood or lymph node-derived T cells required 24 h. Further analysis of intestinal specimens from a 41 patient cohort by flow cytometry indicated membrane LIGHT induction to higher peak levels in lamina propria T cells from the small bowel or rectum but not colon, when compared with lymph node or peripheral blood. Independent stimulation of the LIGHT receptor, herpesvirus entry mediator, induced IFN-γ production in lamina propria T cells, while blocking LIGHT inhibited CD2-dependent induction of IFN-γ synthesis, indicating a role for LIGHT in the regulation of IFN-γ and as a putative mediator of proinflammatory T-T interactions in the intestinal mucosa. Taken together, these findings suggest LIGHT-herpesvirus entry mediator mediated signaling as an important immune regulatory mechanism in mucosal inflammatory responses.

The delicate balance between the proliferation and elimination of antigenactivated lymphocytes achieves homeostasis in peripheral lymphoid tissues. The TNF-related cytokines activate cellular differentiation, survival, and death pathways that orchestrate tissue development, organization, and homeostasis (1). Several members of the TNF superfamily of cytokines play opposing roles in lymphocyte homeostasis by enhancing effector cell activation and survival, or by cellular elimination through apoptosis.Emerging evidence indicates that a recently defined member of the TNF superfamily, LIGHT (TNFSF14), plays a key role in T cell homeostasis. Studies by Wang et al. (2), in this issue of the JCI, and Shaikh et al. (3) reveal that sustained expression of LIGHT causes profound inflammation and loss of tolerance leading to autoimmune syndromes. These new findings validate LIGHT as an important T cell regulatory molecule and suggest its candidacy as a pharmaceutical target for diseases involving T cells.LIGHT is structurally and functionally an integral member of the immediate TNF family, defined by a close structural homology and a communal pattern of receptor-ligand pairing with lymphotoxin-αβ (LTαβ), LTα, and Fas ligand (4, 5). LIGHT is a type II transmembrane protein, produced by activated T cells and immature dendritic cells, that signals through two distinct cellular receptors: the herpesvirus entry mediator (HVEM), which is expressed prominently on T cells, and the LTβ receptor (LTβR), which is expressed on stromal cells but absent from lymphocytes. LIGHT has been proposed to mediate T cell activation, survival, or death, and also -by analogy with LTαβ -to help organize lymphoid tissues (6). Indeed, results in tissue culture models appear to support a role for LIGHT in T cell activation (7,8), although the responses of T cells to LIGHT signaling in vitro are rather subtle. The phenotype of mice expressing ectopic LIGHT is anything but subtle.The studies by Wang et al. (2) and Shaikh et al. (3) demonstrate that constitutive expression of LIGHT leads to profound inflammation caused by activated T cells. Normally, LIGHT is transiently expressed on the surface of T cells following activation, but in the studies highlighted here, the proximal lck (2) or CD2 (3) promoters drive the constitutive expression of LIGHT in T cells. At several months of age, both lines of LIGHT transgenic mice show lymphoid tissue abnormalities, including splenomegaly, lymphadenopathy, and pronounced inflammation in the intestine, consisting of expanded populations of conventional CD4 + and CD8 + αβ T cells. The inflamed intestines show signs of chronic processes including loss of goblet cells, distortion and hyperplasia of crypts, villous atrophy, and mononuclear cell infiltrates. Remarkably, an LTβR-Fc decoy receptor (a chimera of the receptor's ligand-binding domain for LIGHT fused with the Fc region of IgG that neutralizes both LIGHT and LTαβ) prevents colitis in a CD4 T cell-dependent transfer model (9). In this model, expression of LTαβ in...