T-cell tolerance is the central program that prevents harmful immune responses against self-antigens, in which inhibitory PD-1 signal given by B7-H1 interaction plays an important role. Recent studies demonstrated that B7-H1 binds CD80 besides PD-1, and B7-H1/CD80 interaction also delivers inhibitory signals in T cells. However, a role of B7-H1/CD80 signals in regulation of T-cell tolerance has yet to be explored. We report here that attenuation of B7-H1/CD80 signals by treatment with anti-B7-H1 monoclonal antibody, which specifically blocks B7-H1/CD80 but not B7-H1/PD-1, enhanced T-cell expansion and prevented T-cell anergy induction. In addition, B7-H1/CD80 blockade restored Ag responsiveness in the previously anergized T cells. Experiments using B7-H1 or CD80-deficient T cells indicated that an inhibitory signal through CD80, but not B7-H1, on T cells is responsible in part for these effects. Consistently, CD80 expression was detected on anergic T cells and further up-regulated when they were reexposed to the antigen (Ag). Finally, blockade of B7-H1/CD80 interaction prevented oral tolerance induction and restored T-cell responsiveness to Ag previously tolerized by oral administration. Taken together, our findings demonstrate that the B7-H1/CD80 pathway is a crucial regulator in the induction and maintenance of T-cell tolerance. (Blood. 2010;116(8): 1291-1298) Introduction B7-H1 (CD274, PD-L1), a transmembrane glycoprotein belonging to immunoglobulin (Ig) superfamily molecule, plays an integral role in the regulation of immune tolerance and homeostasis. 1 Mice deficient of B7-H1 gene or wild-type mice treated with anti-B7-H1 blocking monoclonal antibody (mAb) exhibit exacerbated autoimmune phenotypes associated with an activation of self-reactive CD4 ϩ and CD8 ϩ T cells. [2][3][4][5] Tolerogenic functions of B7-H1 are dependent on its expression on hematopoietic or parenchymal cells, and mediated by its interaction with PD-1 receptor. 6-8 PD-1 is inducibly expressed on T cells after activation and delivers coinhibitory signals via immunoreceptor tyrosine-based switch motif in the cytoplasmic domain. 9,10 PD-1 signal interferes with phosphatidylinositol-3-kinase (PI3K) activity and subsequently inhibits interleukin-2 (IL-2) production, which eventually renders T cells anergic. 11 The mice deficient of PD-1 gene spontaneously develop autoimmune phenotypes, and single nucleotide polymorphisms of human PD-1 gene are associated with an increased risk of autoimmune diseases. [12][13][14][15][16] Recent studies by Butte et al discovered that B7-H1 interacts with CD80 (B7-1) in addition to PD-1. 17,18 In vitro studies using CD4ϩ T cells deficient of PD-1, CD28, and/or CTLA-4 indicated that B7-H1/CD80 interaction delivers bidirectional inhibitory signals to T cells. 17 These findings are consistent with previous observations implicating the presence of non-PD-1 receptor(s) of B7-H1. For instance, when the B7-H1/PD-1 interaction is blocked in models of T-cell tolerance, the effects of anti-B7-H1 antagonistic mAb in rest...

MHC class I-restricted CD8+ T cells are a crucial component of the host defense against mycobacterial infection in mice, but it has often proved very difficult to identify the CD8 T cell response in humans. Human group 1 CD1 molecules (CD1a, -b, -c) mediate MHC-independent presentation of mycobacteria-derived lipid and glycolipid Ags to CD8+ T cells, and their intracellular localization to the endocytic system may favor efficient monitoring of phagosome-resident mycobacteria. Here, we show that bacillus Calmette-Guérin (BCG)-immunized subjects contain a significant circulating pool of CD8+ T cells that recognize BCG-infected DCs in a CD1-dependent, but MHC-independent, manner. These CD1-restricted T cells efficiently detected live, rather than dead, BCG and produced IFN-γ, an important cytokine for protection against mycobacterial infection. These results emphasize that lipid-reactive CD8+ T cells may contribute to host defense against mycobacterial infection.

Antigen-specific memory T cells (Tms) are essential in the immune surveillance of residual and metastatic tumors. Activation of Tms requires designing vaccines based on tumor rejection antigens, which are often not available to cancer patients. Therefore, it is desirable to have a general applicable approach to activate Tms without extensive knowledge of tumor antigens. Here, we report that activation of antigen-specific Tms could be achieved by the administration of agonistic anti-CD137 monoclonal antibody without additional tumor vaccination, leading to the prevention of recurrence and metastases after surgical resection of primary tumors in mouse models. By reconstitution with CD137-deficient Tms, we demonstrate that expression of CD137 on antigen-specific Tms is only partially required for the effect of anti-CD137 antibody. Other host cells, including those from hematopoietic and nonhematopoietic origins, are also important because ablation of CD137 from these cells partially but significantly eliminates antitumor effect of anti-CD137 antibody. Our findings implicate a potential new approach to prevent recurrence and metastases in cancer patients. (Blood.

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Although thrombotic thrombocytopenic purpura (TTP) is rare, early diagnosis and treatment are important for decreasing the mortality rate. Acquired vitamin B12 deficiency is frequently overlooked because of its rarity in developed countries, particularly in children and adolescents. The hematological changes in vitamin B12 deficiency present as megaloblastic anemia, increased lactate dehydrogenase, vasoconstriction, increased platelet aggregation, and abnormal activation of the coagulation followed by microangiopathy as well as neutropenia and thrombocytopenia. We report herein the case of a 15-year-old girl who had been neglected, which might have caused pseudo-TTP through malnutrition, particularly vitamin B12 deficiency. When we encounter cases of TTP in children, clinicians must be aware of the possibility of malnutrition, particularly with vitamin B12 deficiency, even in developed countries, and investigate the cause of malnutrition including neglect.

Purpose of review Coronavirus disease 2019 (COVID-19), a respiratory infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 virus), is a pandemic in over 120 countries worldwide. Risk factors for severe COVID-19 include older age, ethnicity, sex, comorbidities, and living conditions. Although asthmatics and those with allergies are susceptible to more severe outcomes to viral infections, interestingly, asthma has not been reported to be a major comorbidity of COVID-19. However, there are some conflicting reports on the impact of asthma on COVID-19. The underlying immunological and molecular mechanisms may explain at least in part these observations. Furthermore, environmental factors like air pollution that have detrimental effects on asthma and respiratory illnesses also have an impact on COVID-19. Recent findings Angiotensin-converting enzyme 2 (ACE2) is the receptor for the attachment and entry of SARS-CoV-2 into the host cells that is upregulated by Th1-mediated responses. In asthmatics, ACE2 gene expression is generally reduced and recent studies have shown a negative correlation between the levels of Th2 cytokines including IL-4, IL-5, and IL-13 in airway epithelial cells and other type 2 biomarkers with ACE2 expression. This may explain in part the potential protective role of asthma on COVID-19. Here, we review the relation of respiratory viral illnesses and asthma, the immune-molecular mechanisms of SARS-CoV-2 infection, the impact of asthma on COVID-19 and that of SARS-CoV-2 on asthma and allergic rhinitis, and the impact of environmental factors like air pollution on COVID-19. Summary Expression of ACE2 in airway epithelial cells in SARS-COV-2 is influenced by inflammatory profile. Respiratory allergic diseases like asthma appear to have a protective effect against SARS-COV-2 infection. However, the clinical association between asthma and SARS-COV-2 is not fully established and the underlying immune-molecular mechanisms may explain these observations.

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