T cell expression of MyD88 is required for resistance to Toxoplasma gondii.

Resistance to Toxoplasma gondii depends on dendritic cells to recognize this pathogen and secrete IL-12, in turn promoting IFN-gamma production from responding T cells. The adaptor protein, myeloid differentiation primary-response gene 88 (MyD88), is important for most Toll-like receptor (TLR) signaling, as well as IL-1R/IL-18R signals. There is considerable evidence that MyD88 is required for the innate sensing of T. gondii and IL-12 responses. Although Myd88(-/-) mice challenged with T. gondii have defective IL-12 and Th1 effector responses and succumb to disease, administration of IL-12 to Myd88(-/-) mice partially restores the Th1 response and yet fails to prolong survival. This finding suggested that MyD88 may mediate signals within T cells important for resistance to this pathogen. To evaluate the role of MyD88 in T cells under noncompetitive conditions, bone marrow chimeras were generated, in which the T cells lacked MyD88, but MyD88-dependent innate immune responses were intact. Upon challenge with T. gondii, these chimeric mice were more susceptible to disease, developing severe toxoplasmic encephalitis and succumbing within 30 days. Splenocytes and brain mononuclear cells isolated from infected chimeric mice produced less IFN-gamma when cultured with a T. gondii-derived antigen. The increase in susceptibility observed was independent of signals via the IL-1R and IL-18R, suggesting a role for TLRs in MyD88-mediated T cell responses to T. gondii. These observations show that, in addition to a role for MyD88 in innate responses, T cell expression of MyD88 is necessary for prolonged resistance to a pathogen.

Assessment of commercial SARS-CoV-2 antibody assays, Jamaica.

BACKGROUND: The performance of the Roche Elecsys® Anti-SARS-CoV-2, Abbott Architect SARS-CoV-2 IgM, Abbott Architect SARS-CoV-2 IgG, Euroimmun SARS-CoV-2 IgA, Euroimmun SARS-CoV-2 IgG ELISA, and Trillium IgG/IgM rapid assays was evaluated in Jamaica. METHODS: Diagnostic sensitivities of the assays were assessed by testing serum samples from SARS-CoV-2 PCR-confirmed persons and diagnostic specificity was assessed by testing serum samples collected during 2018-2019 from healthy persons and from persons with antibodies to a wide range of viral infections. RESULTS: Serum samples collected ≥14 days after onset of symptoms, or an initial SARS-CoV-2 RT-PCR positive test for asymptomatics, showed diagnostic sensitivities ranging from 67.9 to 75.0% when including all possible disease severities and increased to 90.0-95.0% when examining those with moderate to critical disease. Grouping moderate to critical disease showed a significant association with a SARS-CoV-2 antibody positive result for all assays. Diagnostic specificity ranged from 96.7 to 100.0%. For all assays examined, SARS-CoV-2 real-time PCR cycle threshold (Ct) values of the initial nasopharyngeal swab sample testing positive were significantly different for samples testing antibody positive versus negative. CONCLUSIONS: These data from a predominantly African descent Caribbean population show comparable diagnostic sensitivities and specificities for all testing platforms assessed and limited utility of these tests for persons with asymptomatic and mild infections.

MyD88 plays a critical T cell-intrinsic role in supporting CD8 T cell expansion during acute lymphocytic choriomeningitis virus infection.

During acute lymphocytic choriomeningitis virus (LCMV) infection, CD8 T cells rapidly expand and differentiate into effectors that are required for viral clearance. The accumulation of activated T cells is greatly reduced in mice lacking the adaptor molecule MyD88. Although MyD88 has generally been considered to indirectly regulate adaptive immune responses by controlling inflammatory cytokine production and Ag presentation in innate immune cells, in this study, we identify an unappreciated cell-intrinsic role for MyD88 in LCMV-specific CD8 T cells. Using reciprocal adoptive transfer models and bone marrow chimeras, we show that Myd88(-/-) CD8 T cells are defective in their clonal expansion in response to LCMV infection, independent of their environment. Furthermore, we show that while MyD88 is dispensable for initial activation and division of LCMV-specific CD8 T cells during the early stages of viral infection, MyD88-dependent signals are critical for supporting their survival and sustained accumulation.

PTEN inhibits IL-2 receptor-mediated expansion of CD4+ CD25+ Tregs.

One of the greatest barriers against harnessing the potential of CD4+ CD25+ Tregs as a cellular immunotherapy is their hypoproliferative phenotype. We have previously shown that the hypoproliferative response of Tregs to IL-2 is associated with defective downstream PI3K signaling. Here, we demonstrate that targeted deletion of the lipid phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome 10) regulates the peripheral homeostasis of Tregs in vivo and allows their expansion ex vivo in response to IL-2 alone. PTEN deficiency does not adversely affect either the thymic development or the function of Tregs, which retain their ability to suppress responder T cells in vitro and prevent colitis in vivo. Conversely, reexpression of PTEN in PTEN-deficient Tregs as well as in activated CD4+ T cells inhibits IL-2-dependent proliferation, confirming PTEN as a negative regulator of IL-2 receptor signaling. These data demonstrate that PTEN regulates the "anergic" response of Tregs to IL-2 in vitro and Treg homeostasis in vivo and indicate that inhibition of PTEN activity may facilitate the expansion of these cells for potential use in cellular immunotherapy.

SLE Plasma Profiling Identifies Unique Signatures of Lupus Nephritis and Discoid Lupus.

Systemic lupus erythematosus (SLE) impacts multiple organ systems, although the causes of many individual SLE pathologies are poorly understood. This study was designed to elucidate organ-specific inflammation by identifying proteins that correlate with SLE organ involvement and to evaluate established biomarkers of disease activity across a diverse patient cohort. Plasma proteins and autoantibodies were measured across seven SLE manifestations. Comparative analyses between pathologies and correlation with the SLE Disease Activity Index (SLEDAI) were used to identify proteins associated with organ-specific and composite disease activity. Established biomarkers of composite disease activity, SLE-associated antibodies, type I interferon (IFN), and complement C3, correlated with composite SLEDAI, but did not significantly associate with many individual SLE pathologies. Two clusters of proteins were associated with renal disease in lupus nephritis samples. One cluster included markers of infiltrating leukocytes and the second cluster included markers of tissue remodelling. In patients with discoid lupus, a distinct signature consisting of elevated immunoglobulin A autoantibodies and interleukin-23 was observed. Our findings indicate that proteins from blood samples can be used to identify protein signatures that are distinct from established SLE biomarkers and SLEDAI and could be used to conveniently monitor multiple inflammatory pathways present in different organ systems.

T follicular helper-like cells contribute to skin fibrosis.

Systemic sclerosis (SSc) is a debilitating inflammatory and fibrotic disease that affects the skin and internal organs. Although the pathophysiology of SSc remains poorly characterized, mononuclear cells, mainly macrophages and T cells, have been implicated in inflammation and fibrosis. Inducible costimulator (ICOS), which is expressed on a subset of memory T helper (TH) and T follicular helper (TFH) cells, has been shown to be increased in SSc and associated with disease pathology. However, the identity of the relevant ICOS+ T cells and their contribution to inflammation and fibrosis in SSc are still unknown. We show that CD4+ ICOS-expressing T cells with a TFH-like phenotype infiltrate the skin of patients with SSc and are correlated with dermal fibrosis and clinical disease status. ICOS+ TFH-like cells were found to be increased in the skin of graft-versus-host disease (GVHD)-SSc mice and contributed to dermal fibrosis via an interleukin-21- and matrix metalloproteinase 12-dependent mechanism. Administration of an anti-ICOS antibody to GVHD-SSc mice prevented the expansion of ICOS+ TFH-like cells and inhibited inflammation and dermal fibrosis. Interleukin-21 neutralization in GVHD-SSc mice blocked disease pathogenesis by reducing skin fibrosis. These results identify ICOS+ TFH-like profibrotic cells as key drivers of fibrosis in a GVHD-SSc model and suggest that inhibition of these cells could offer therapeutic benefit for SSc.

Tregs and transplantation tolerance.

The induction and maintenance of immune tolerance to transplanted tissues constitute an active process involving multiple mechanisms that work cooperatively to prevent graft rejection. These mechanisms are similar to inherent tolerance toward self antigens and have a requirement for active immunoregulation, largely T cell mediated, that promotes specific unresponsiveness to donor alloantigens. This review outlines our current understanding of the Treg subsets that contribute to allotolerance and the mechanisms by which these cells exert their effects as well as their potential for therapy.

Heterologous immunity and homeostatic proliferation as barriers to tolerance.

The different threshold of activation for memory T cells compared to that of naïve T cells makes them resistant to immunomodulation, thus representing a barrier to tolerance. Recently it has been demonstrated that homeostatic proliferation and heterologous immunity represent two naturally occurring and distinct processes that can generate memory T cells. Homeostatic proliferation refers to the process by which, in a lymphodeficient host, normal T cells 'spontaneously' proliferate in response to self-MHC-peptide complexes. Heterologous immunity refers to a process in which a response to one or more infectious agents generates effector/memory T cells with cross-reactive specificities. Recent new studies have defined the importance of these processes in transplantation models and implicated strategies to induce transplantation tolerance.

Loss of tolerance of anti-dsDNA B cells in mice overexpressing CD19.

Mice transgenic for the R4A-Cmu heavy chain of an anti-dsDNA antibody, maintain tolerance by anergy and deletion. In C57BL/6 mice overexpressing CD19, a molecule, which lowers the threshold for B cell activation, elevated levels of serum autoantibodies have been observed. In the present study, we wished to determine whether CD19 overexpression could alter the induction of tolerance in R4A-Cmu mice and lead to the secretion of transgenic anti-dsDNA antibodies. We, therefore, bred R4A-Cmu transgenic mice-to-mice transgenic for human CD19 (hCD19) and generated R4A-Cmu mice heterozygous and homozygous for hCD19. We, now report the spontaneous secretion of transgenic IgM anti-dsDNA antibody in the sera of R4A-Cmu mice overexpressing CD19, indicative of a loss of B cell tolerance. We observe that transgenic B cells secreting anti-dsDNA antibody in these mice are T independent and display a marginal zone like phenotype althought they do not reside in the MZ. In addition, they appear to be derived from the conventional B2 subset rather than the B1 subset. Interestingly, a subset of the anti-dsDNA B cells in these mice still display the phenotype and functional characteristics of anergic B cells. These B cells cannot be activated to secrete antibody following BCR crosslinking, however, they are hyper-responsive to activation by innate signaling mechanisms. This suggests that CD19 overexpression may promote anergic B cells to escape tolerance by converging with BCR independent pathways, thereby rendering these B cells hyper-responsive to innate signaling.

The contribution of direct TLR signaling to T cell responses.

It is well established that Toll-like receptors (TLRs) play a critical role in the generation of innate immune responses and thereby also play an important, indirect role in the initiation of subsequent adaptive T cell responses. However, T cells also express certain TLRs, and we have focused on the physiological importance of direct TLR signaling in T cells. TLRs can function as co-stimulatory receptors that complement TCR-induced signals to enhance effector T cell proliferation, survival and cytokine production. We also found that TLR signaling pathways in T cells are required for the effective clonal expansion of antigen-specific T cells during infection in vivo. Thus, the importance of TLRs in T cell-mediated immunity reflects both T cell-extrinsic and T cell-intrinsic components, which warrants a reconsideration of the dogma that restricts germ-line encoded pattern recognition to cells of the innate immune system.

Constitutive activation of STAT5 supersedes the requirement for cytokine and TCR engagement of CD4+ T cells in steady-state homeostasis.

The transcription factor STAT5 is one of several signaling mediators activated via common gamma-chain cytokine receptors. As such, it plays an important role in lymphocyte survival and proliferation during normal homeostasis as well as under lymphopenic conditions. Transgenic mice expressing a constitutively activated form of STAT5b have been shown previously to contain increased numbers of peripheral CD4+CD25- T cells. To define the mechanism(s) for this occurrence, we have used adoptive transfer studies to examine the effects of STAT5 activity on steady-state CD4+ T cell homeostasis. We observed that constitutive STAT5 signaling induced 4- to 7-fold increased levels of basal steady-state proliferation, which was accompanied by a comparable increase in T cell recovery. Most strikingly, steady-state CD4 T cell proliferation occurred independently of both MHC class II and IL-15. These observations demonstrate that the STAT5-driven pathway is important to lymphocyte homeostasis and can supersede the need for both TCR engagement and cytokine stimulation. This suggests that the need for TCR stimulation to induce common gamma-chain cytokine receptor expression, and thus STAT5 activation, is a key factor in maintaining normal CD4+ T cell homeostasis.

Expression of the Epstein-Barr virus nuclear antigen-1 (EBNA-1) in the mouse can elicit the production of anti-dsDNA and anti-Sm antibodies.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder characterized by the production of anti-nuclear antibodies. The etiology of SLE is unknown, although several viruses including the Epstein-Barr virus (EBV) have been implicated. An increase in the frequency of EBV infection has been observed in SLE patients relative to normal individuals. Some patients with SLE develop antibodies that recognize a proline rich epitope in the ribonucleoprotein Sm B/B that is similar to an epitope in EBNA-1, a major nuclear antigen of EBV. In the present study we have cloned the EBNA-1 gene under the control of the CMV promoter in the vector pcDNA3. We now report for the first time that expression of the entire EBNA-1 protein in the mouse can elicit the production of IgG antibodies to Sm and to double-stranded DNA (dsDNA). Our data suggest that the anti-Sm response arises as a consequence of antigenic cross-reactivity by anti-EBNA-1 antibodies. These results support a possible association between EBV infection and SLE.