Zijian Pan

Targeting Toll-like receptors for treatment of SLE.

Toll-like receptors (TLRs) are important innate immune receptors for the identification and clearance of invading pathogens. Twelve TLRs that recognize various conserved components of microorganisms are currently known. Among these, the endosomal TLRs 3, 7/8, and 9 recognize dsRNA, ssRNA, and CpG DNA, respectively. Nucleic acid-sensing TLRs, TLR 7 in particular, have been implicated in systemic lupus erythematosus (SLE) and are thought to exacerbate disease pathology. Activation of these TLRs results in the production of inflammatory cytokines and type I interferon. Genome-wide association studies, single nucleotide polymorphism analyses as well as experimental mouse models have provided evidence of TLR signaling involvement in SLE and other autoimmune diseases. Since activation of these receptor pathways promotes autoimmune phenotypes, inhibitory drugs that target these pathways constitute important new therapeutic strategies for the treatment of systemic autoimmunity.

The presence of masked antiribosomal P autoantibodies in healthy children

OBJECTIVE To determine if antiribosomal P (anti-P) autoantibodies are present in healthy children. METHODS Sera from healthy children were screened for anti-P by conventional enzyme-linked immunosorbent assay and immunoblot techniques. Sera were also treated with immobilized ribosomal P antigens on nitrocellulose strips; affinity-purified fractions were tested for anti-P by high-sensitivity immunoblot. The relative binding affinities were compared for affinity-purified anti-P antibodies from healthy children and adults, and patients with systemic lupus erythematosus. IgG fractions of anti-P-depleted sera from healthy children were assessed for inhibition of autologous anti-P activity. RESULTS Conventional serologic screening showed no IgG nor IgM anti-P in 88 untreated sera. IgG anti-P were unmasked in all 79 sera treated by the membrane batch affinity technique. IgM anti-P were identified in 27 of the treated sera; the percentage of positive sera decreased with increasing age (chi(2) for linear trend P = 0.00081). Affinity-purified anti-P from children had relative binding affinities similar to those of anti-P from other groups. Sera from healthy children contained inhibitory IgG antibodies to anti-P. CONCLUSION These results show that anti-P autoantibodies are present in all healthy children. The majority of these autoantibodies are masked by IgG antibodies, suggesting concordant development of a regulatory network.

Neo-epitopes are required for immunogenicity of the La/SS-B nuclear antigen in the context of late apoptotic cells

Mechanisms responsible for the induction of anti‐nuclear autoantibodies (ANA) following exposure of the immune system to an excess of apoptotic cells are incompletely understood. In this study, the immunogenicity of late apoptotic cells expressing heterologous or syngeneic forms of La/SS‐B was investigated following subcutaneous administration to A/J mice, a non‐autoimmune strain in which the La antigenic system is well understood. Immunization of A/J mice with late apoptotic thymocytes taken from mice transgenic (Tg) for the human La (hLa) nuclear antigen resulted in the production of IgG ANA specific for human and mouse forms of La in the absence of foreign adjuvants. Preparations of phenotypically healthy cells expressing heterologous hLa were also immunogenic. However, hLa Tg late apoptotic cells accelerated and enhanced the apparent heterologous healthy cell‐induced anti‐La humoral response, while non‐Tg late apoptotic cells did not. Subcutaneous administration of late apoptotic cells was insufficient to break existing tolerance to the hLa antigen in hLa Tg mice or to the endogenous mouse La (mLa) antigen in A/J mice immunized with syngeneic thymocytes, indicating a requirement for the presence of heterologous epitopes for anti‐La ANA production. Lymph node dendritic cells (DC) but not B cells isolated from non‐Tg mice injected with hLa Tg late apoptotic cells presented immunodominant T helper cell epitopes of hLa. These studies support a model in which the generation of neo‐T cell epitopes is required for loss of tolerance to nuclear proteins after exposure of the healthy immune system to an excess of cells in late stages of apoptosis.

Interleukin-6 Deficiency Corrects Nephritis, Lymphocyte Abnormalities, and Secondary Sjögren's Syndrome Features in Lupus-Prone Sle1.Yaa Mice†

To assess disease features in Sle1.Yaa mice with genetic interleukin‐6 (IL‐6) deficiency.

T-Helper Cell Tolerance to Ubiquitous Nuclear Antigens

Systemic autoimmune diseases are characterized by the development of antinuclear autoantibodies. In order to understand the immunologic events leading to the development of such antibodies, knowledge of mechanisms of immune tolerance to nuclear antigens is required. By utilizing adoptive T‐cell transfer strategies with transgenic mouse models expressing nuclear neo‐self antigens, T‐cell tolerance to the lupus‐related nuclear antigens human La and nRNP A has been demonstrated. These findings also indicate the existence in normal animals of autoreactive B cells continuously presenting nuclear antigen, suggesting that nuclear antigens are not sequestered from the immune system. Investigations of CD4+ T‐cell tolerance to non‐nuclear antigens have revealed a number of mechanisms that protect the host from autoreactivity, including autoreactive T‐cell deletion, regulatory T‐cell development and anergy induction. Recent studies using T‐cell receptor and neo‐self nuclear antigen transgenic mice are revealing the importance of such mechanisms in maintaining tolerance to nuclear antigens. Mechanisms of tolerogenic antigen presentation, identification of tolerogenic antigen source(s) and the pathways leading to loss of tolerance to nuclear antigens in systemic autoimmune disease states are currently being sought.

Plasmacytoid dendritic cells and type 1 interferon promote peripheral expansion of forkhead box protein 3+ regulatory T cells specific for the ubiquitous RNA-binding nuclear antigen La/Sjögren's syndrome (SS)-B

RNA‐binding nuclear antigens are a major class of self‐antigen to which immune tolerance is lost in rheumatic diseases. Serological tolerance to one such antigen, La/Sjögrens syndrome (SS)‐B (La), is controlled by CD4+ T cells. This study investigated peripheral tolerance to human La (hLa) by tracking the fate of hLa‐specific CD4+ T cells expressing the transgenic (Tg) 3B5.8 T cell receptor (TCR) after adoptive transfer into lymphocyte‐replete recipient mice expressing hLa as a neo‐self‐antigen. After initial antigen‐specific cell division, hLa‐specific donor CD4+ T cells expressed forkhead box protein 3 (FoxP3). Donor cells retrieved from hLa Tg recipients displayed impaired proliferation and secreted interleukin (IL)−10 in vitro in response to antigenic stimulation. Transfer of highly purified FoxP3‐negative donor cells demonstrated that accumulation of hLa‐specific regulatory T cells (Treg) was due primarily to expansion of small numbers of donor Treg. Depletion of recipient plasmacytoid dendritic cells (pDC), but not B cells, severely hampered the accumulation of FoxP3+ donor Treg in hLa Tg recipients. Recipient pDC expressed tolerogenic markers and higher levels of co‐stimulatory and co‐inhibitory molecules than B cells. Adoptive transfer of hLa peptide‐loaded pDC into mice lacking expression of hLa recapitulated the accumulation of hLa‐specific Treg. Blockade of the type 1 interferon (IFN) receptor in hLa Tg recipients of hLa‐specific T cells impaired FoxP3+ donor T cell accumulation. Therefore, peripheral expansion of Treg specific for an RNA‐binding nuclear antigen is mediated by antigen‐presenting pDC in a type 1 IFN‐dependent manner. These results reveal a regulatory function of pDC in controlling autoreactivity to RNA‐binding nuclear antigens.

Plasmacytoid dendritic cells and type 1 IFN promote peripheral expansion of Foxp3+ regulatory T cells specific for the ubiquitous RNA‐binding nuclear antigen La/SS‐B

RNA‐binding nuclear antigens are a major class of self‐antigen to which immune tolerance is lost in rheumatic diseases. Serological tolerance to one such antigen, La/Sjögrens syndrome (SS)‐B (La), is controlled by CD4+ T cells. This study investigated peripheral tolerance to human La (hLa) by tracking the fate of hLa‐specific CD4+ T cells expressing the transgenic (Tg) 3B5.8 T cell receptor (TCR) after adoptive transfer into lymphocyte‐replete recipient mice expressing hLa as a neo‐self‐antigen. After initial antigen‐specific cell division, hLa‐specific donor CD4+ T cells expressed forkhead box protein 3 (FoxP3). Donor cells retrieved from hLa Tg recipients displayed impaired proliferation and secreted interleukin (IL)−10 in vitro in response to antigenic stimulation. Transfer of highly purified FoxP3‐negative donor cells demonstrated that accumulation of hLa‐specific regulatory T cells (Treg) was due primarily to expansion of small numbers of donor Treg. Depletion of recipient plasmacytoid dendritic cells (pDC), but not B cells, severely hampered the accumulation of FoxP3+ donor Treg in hLa Tg recipients. Recipient pDC expressed tolerogenic markers and higher levels of co‐stimulatory and co‐inhibitory molecules than B cells. Adoptive transfer of hLa peptide‐loaded pDC into mice lacking expression of hLa recapitulated the accumulation of hLa‐specific Treg. Blockade of the type 1 interferon (IFN) receptor in hLa Tg recipients of hLa‐specific T cells impaired FoxP3+ donor T cell accumulation. Therefore, peripheral expansion of Treg specific for an RNA‐binding nuclear antigen is mediated by antigen‐presenting pDC in a type 1 IFN‐dependent manner. These results reveal a regulatory function of pDC in controlling autoreactivity to RNA‐binding nuclear antigens.

IL-6 Deficiency Corrects Nephritis, Lymphocyte Abnormalities and Secondary Sjögren’s Features in Sle1.Yaa Lupus-Prone Mice

To assess disease features in Sle1.Yaa mice with genetic interleukin‐6 (IL‐6) deficiency.

Interleukin-6 Deficiency Corrects Nephritis, Lymphocyte Abnormalities, and Secondary Sjögren's Syndrome Features in Lupus-ProneSle1.YaaMice: IL-6 Deficiency Abrogates SLE and SS Features in Lupus-Prone Mice

To assess disease features in Sle1.Yaa mice with genetic interleukin‐6 (IL‐6) deficiency.