Currently, there is a need for reliable tests that allow identification of individuals that have been infected with SARS-CoV-2 even if the infection was asymptomatic. To date, the vast majority of the serological tests for SARS-CoV-2-specific Abs are based on serum detection of Abs to either the viral spike glycoprotein (the major target for neutralizing Abs) or the viral nucleocapsid protein that is known to be highly immunogenic in other coronaviruses. Conceivably, exposure of Ags released from infected cells could stimulate Ab responses that might correlate with tissue damage and, hence, they may have some value as a prognostic indicator. We addressed whether other nonstructural viral proteins, not incorporated into the infectious viral particle, specifically the viral cysteine-like protease, might also be potent immunogens. Using ELISA tests, coating several SARS-CoV-2 proteins produced in vitro, we describe that COVID-19 patients make high titer IgG, IgM, and IgA Ab responses to the Cys-like protease from SARS-CoV-2, also known as 3CLpro or Mpro, and it can be used to identify individuals with positive serology against the coronavirus. Higher Ab titers in these assays associated with more-severe disease, and no crossreactive Abs against prior betacoronavirus were found. Remarkably, IgG Abs specific for Mpro and other SARS-CoV-2 Ags can also be detected in saliva. In conclusion, Mpro is a potent Ag in infected patients that can be used in serological tests, and its detection in saliva could be the basis for a rapid, noninvasive test for COVID-19 seropositivity.

Cross-linking of the collagen binding receptor LAIR-1 in vitro delivers an inhibitory signal that is able to down-regulate activation-mediated signals. To study the in vivo function of LAIR-1, we generated LAIR-1−/− mice. They are healthy and fertile, and have normal longevity; however, they show certain phenotypic characteristics distinct from wild-type mice, including increased numbers of splenic B, T regulatory and dendritic cells. As LAIR-1−/− mice age, the splenic T cell population shows a higher frequency of activated and memory T cells. Since LAIR-1+/+ and LAIR-1−/− T cells traffic with equal proficiency to peripheral lymphoid organs, this is not likely due to abnormal T lymphocyte trafficking. LAIR-1−/− mice have lower serum levels of IgG1 and, in response to T-dependent immunization with TNP-OVA, switch less efficiently to antigen specific IgG2a and IgG2b, while switching to IgG1 is not affected. Several mouse disease models, including EAE and colitis, were utilized to examine the effect of LAIR-1 deficiency and no differences in the responses of LAIR-1−/− and LAIR-1+/+ mice were observed. Taken together, these observations indicate that LAIR-1 plays a role in regulating immune cells and suggest that any adverse effects of its absence may be balanced in vivo by other inhibitory receptors.

Intravesical instillation of bacillus Calmette–Guérin (BCG) is used to treat superficial bladder cancer, either papillary tumors (after transurethral resection) or high-grade flat carcinomas (carcinoma in situ), reducing recurrence in about 70% of patients. Initially, BCG was proposed to work through an inflammatory response, mediated by phagocytic uptake of mycobacterial antigens and cytokine release. More recently, other immune effectors such as monocytes, natural killer (NK), and NKT cells have been suggested to play a role in this immune response. Here, we provide a comprehensive study of multiple bladder cancer cell lines as putative targets for immune cells and evaluated their recognition by NK cells in the presence and absence of BCG. We describe that different bladder cancer cells can express multiple activating and inhibitory ligands for NK cells. Recognition of bladder cancer cells depended mainly on NKG2D, with a contribution from NKp46. Surprisingly, exposure to BCG did not affect the immune phenotype of bladder cells nor increased NK cell recognition of purified IL-2-activated cell lines. However, NK cells were activated efficiently when BCG was included in mixed lymphocyte cultures, suggesting that NK activation after mycobacteria treatment requires the collaboration of various immune cells. We also analyzed the percentage of NK cells in peripheral blood of a cohort of bladder cancer patients treated with BCG. The total numbers of NK cells did not vary during treatment, indicating that a more detailed study of NK cell activation in the tumor site will be required to evaluate the response in each patient.

Infection of the small intestine by enterotoxigenic Escherichia coli F4ab/ac is a major welfare problem and financial burden for the pig industry. Natural resistance to this infection is inherited as a Mendelian recessive trait, and a polymorphism in the MUC4 gene segregating for susceptibility/resistance is presently used in a selection programme by the Danish pig breeding industry. To elucidate the genetic background involved in E. coli F4ab/ac susceptibility in pigs, a detailed haplotype map of the porcine candidate region was established. This region covers approximately 3.7 Mb. The material used for the study is a three generation family, where the founders are two Wild boars and eight Large White sows. All pigs have been phenotyped for susceptibility to F4ab/ac using an adhesion assay. Their haplotypes are known from segregation analysis using flanking markers. By a targeted approach, the candidate region was subjected to screening for polymorphisms, mainly focusing on intronic sequences. A total of 18 genes were partially sequenced, and polymorphisms were identified in GP5, CENTB2, APOD, PCYT1A, OSTalpha, ZDHHC19, TFRC, ACK1, MUC4, MUC20, KIAA0226, LRCH3 and MUC13. Overall, 227 polymorphisms were discovered in the founder generation. The analysis revealed a large haplotype block, spanning at least 1.5 Mb around MUC4, to be associated with F4ab/ac susceptibility.

Proteolytic shedding of ligands for the NK group 2D (NKG2D) receptor is a strategy used by tumors to modulate immune recognition by NK cells and cytotoxic T cells. A number of metalloproteases, especially those of the a disintegrin and metalloprotease (ADAM) family, can mediate NKG2D ligand cleavage and this process can be modulated by expression of the thiol isomerase ERp5. In this article, we describe that an increased shedding of the NKG2D ligand MICA is observed postinfection with several strains of human CMV due to an enhanced activity of ADAM17 (TNF-α converting enzyme) and matrix metalloprotease 14 caused by a reduction in the expression of the endogenous inhibitor of metalloproteases tissue inhibitors of metalloproteinase 3 (TIMP3). This decrease in TIMP3 expression correlates with increased expression of a cellular miRNA known to target TIMP3, and we also identify a human CMV–encoded microRNA able to modulate TIMP3 expression. These observations characterize a novel viral strategy to influence the shedding of cell-surface molecules involved in immune response modulation. They also provide an explanation for previous reports of increased levels of various ADAM17 substrates in the serum from patients with CMV disease. Consistent with this hypothesis, we detected soluble MICA in serum of transplant recipients with CMV disease. Finally, these data suggest that it might be worthwhile to prospectively study ADAM17 activity in a larger group of patients to assay whether this might be a useful biomarker to identify patients at risk for development of CMV disease.

BackgroundEnterotoxigenic Escherichia coli (ETEC) that express the F4ab and F4ac fimbriae is a major contributor to diarrhoea outbreaks in the pig breeding industry, infecting both newborn and weaned piglets. Some pigs are resistant to this infection, and susceptibility is inherited as a simple dominant Mendelian trait. Indentifying the genetics behind this trait will greatly benefit pig welfare as well as the pig breeding industry by providing an opportunity to select against genetically susceptible animals, thereby reducing the number of diarrhoea outbreaks. The trait has recently been mapped by haplotype sharing to a 2.5 Mb region on pig chromosome 13, a region containing 18 annotated genes.FindingsThe coding regions of five candidate genes for susceptibility to ETEC F4ab/ac infection (TFRC, ACK1, MUC20, MUC4 and KIAA0226), all located in the 2.5 Mb region, were investigated for the presence of possible causative mutations. A total of 34 polymorphisms were identified in either coding regions or their flanking introns. The genotyping data for two of those were found to perfectly match the genotypes at the ETEC F4ab/ac locus, a G to C polymorphism in intron 11 of TFRC and a C to T silent polymorphism in exon 22 of KIAA0226. Transcriptional profiles of the five genes were investigated in a porcine tissue panel including various intestinal tissues. All five genes were expressed in intestinal tissues at different levels but none of the genes were found differentially expressed between ETEC F4ab/ac resistant and ETEC F4ab/ac susceptible animals in any of the tested tissues.ConclusionsNone of the identified polymorphisms are obvious causative mutations for ETEC F4ab/ac susceptibility, as they have no impact on the level of the overall mRNA expression nor predicted to influence the composition of the amino acids composition. However, we cannot exclude that the five tested genes are bona fide candidate genes for susceptibility to ETEC F4ab/ac infection since the identified polymorphism might affect the translational apparatus, alternative splice forms may exist and post translational mechanisms might contribute to disease susceptibility.

MICA and MICB (MHC-class-I-related chain A/B) are transmembrane proteins expressed in pathological conditions that are ligands for NKG2D, an activating receptor found on cytotoxic lymphocytes. The recognition on target cells of NKG2D ligands leads to the activation of lysis and cytokine secretion by NK cells and T cells. Besides being expressed at the cell surface, MICA/B can be released as soluble proteins. Soluble NKG2D ligands downmodulate expression of the NKG2D receptor on lymphocytes, leading to a diminished cytotoxic response. Prior studies suggested that recruitment of MICA/B molecules to cholesterol-enriched microdomains was an important factor regulating the proteolytic release of these molecules. We now show that recruitment of MICA to these microdomains depends on palmitoylation of two cysteine residues that allow MICA molecules to reside in the membrane in the same domains as caveolin-1. Compared with WT molecules, nonpalmitoylated mutant MICA molecules were shed to the supernatant with low efficiency; however, both WT and mutant MICA were able to trigger NK cell cytotoxicity. These data suggest that the presence of NKG2D ligands at the plasma membrane is sufficient to activate cytotoxicity and reflect the need of different ligands to exploit different cellular pathways to reach the cell surface upon different stress situations.

Immunotherapy, via intra-vesical instillations of BCG, is the therapy of choice for patients with high-risk non-muscle invasive bladder cancer. The subsequent recruitment of lymphocytes and myeloid cells, as well as the release of cytokines and chemokines, is believed to induce a local immune response that eliminates these tumors, but the detailed mechanisms of action of this therapy are not well understood. Here, we have studied the phenotype and function of the responding lymphocyte populations as well as the spectrum of cytokines and chemokines produced in an model of human peripheral blood mononuclear cells (PBMCs) co-cultured with BCG. Natural killer (NK) cell activation was a prominent feature of this immune response and we have studied the expansion of this lymphocyte population in detail. We show that, after BCG stimulation, CD56 NK cells proliferate, upregulate CD56, but maintain the expression of CD16 and the ability to mediate ADCC. CD56 NK cells also contribute to this expansion by increasing CD16 and KIR expression. These unconventional CD56 cells efficiently degranulated against bladder cancer cells and the expansion of this population required the release of soluble factors by other immune cells in the context of BCG. Consistent with these data, a small, but significant increase in the intensity of CD16 expression was noted in peripheral blood CD56 cells from bladder cancer patients undergoing BCG therapy, that was not observed in patients treated with mitomycin-C instillations. These observations suggest that activation of NK cells may be an important component of the anti-tumoral immune response triggered by BCG therapy in bladder cancer.