Gld mutation of Fas ligand increases the frequency and up-regulates cell survival genes in CD25+CD4+ TR cells.

The Fas pathway and regulatory T (T(R)) cells play intertwining roles in controlling T cell tolerance through deletion and suppression of autoreactive T cells. Impairment of either mechanism causes severe T cell lymphoproliferation albeit with opposing outcomes. T cell lymphoproliferation induced by defective Fas pathway does not cause overt lymphocytic infiltration but rather prevents an important set of T cell-mediated autoimmune diseases. In contrast, deficiency in T(R) cell causes fulminant autoimmunity in very early life and fatal lymphocytic infiltration. These observations suggest existence of unidirectional fail/safe mechanism that compensate for defects in the Fas pathway but not in regulatory cells. To gain insights into how animals compensate for defects in the Fas system, we analyzed the impact of generalized lymphoproliferative disease (gld) mutation on survival, function and transcription profile of CD25+CD4+ T(R) cells. Our results show that all CD4 T cells expanded in gld mice. However, CD25+CD4+ T(R) cells are disproportionately increased in the pool of CD4 T cells perhaps due to their unique apoptosis phenotype. Freshly isolated CD25+CD4+ T(R) cells, unlike CD25-CD4+ T cells, are highly sensitive to FasL-induced apoptosis in the steady state. CD25+CD4+ T(R) cells that accumulate in gld mice express similar level of Foxp3, and have suppression potency and T(R) gene expression profile as wild-type CD25+CD4+ T(R) cells. Furthermore, the transcription profile of gld CD25+CD4+ T(R) cells is characterized by differential expression of genes involved in cell survival, metabolism and innate immune responses. These results provide a strong cellular and molecular basis for understanding why impaired Fas pathway prevents an important subset of T cell-mediated autoimmune diseases.

B lymphocyte activation by human papillomavirus-like particles directly induces Ig class switch recombination via TLR4-MyD88.

Vaccination with human papillomavirus type 16 (HPV16) L1 virus-like particles (VLP) induces both high titer neutralizing IgG and protective immunity. Because protection from experimental infection by papillomavirus is mediated by neutralizing IgG, we sought the mechanisms that trigger humoral immunity to HPV16 L1 VLP. We find that HPV16 L1 VLP bind to murine B lymphocytes thereby inducing activation-induced cytidine deaminase expression and Ig class switch recombination to cause the generation of IgG. HPV16 L1 VLP also activate production of proinflammatory factors IFN-alpha, IL-6, MIP-1alpha, RANTES, and KC, up-regulate the expression of costimulatory molecules by naive B cells, and increase the B1 B cell subpopulation. These B cell responses to HPV16 L1 VLP are dependent upon MyD88. Although MyD88(-/-) B cells produce only mu transcript after exposure to HPV16 L1 VLP, MyD88(+/+) B cells express alpha, gamma, and mu Ig H chain and activation-induced cytidine deaminase transcripts. Notably, TLR4 mutant C3H/HeJ mice exhibited significantly reduced HPV16 VLP-specific IgG1, IgG2a, IgG2b, and IgG3 titers after vaccination as compared with the control C3H/HeOuJ mice. HPV16 L1 VLP directly activated class switch recombination and costimulatory molecule expression by B cells of C3H/HeOuJ mice but not C3H/HeJ mice. Thus HPV16 L1 VLP directly activate B cells to induce CD4(+) T cell independent humoral immune responses via TLR4- and MyD88-dependent signaling.

Papillomavirus-like particles stimulate murine bone marrow-derived dendritic cells to produce alpha interferon and Th1 immune responses via MyD88.

Dendritic cells (DCs) link innate and adaptive immunity by sensing pathogens or vaccinogens and signaling a variety of defense responses. Since human papillomavirus type 16 L1 virus-like particles (HPV16 VLPs) induce a potent, protective immune response after vaccination, we examined their recognition by DCs. HPV16 VLPs cause phenotypic maturation of murine bone marrow-derived DCs (BMDCs), and immunization of mice with HPV16 VLP-loaded BMDCs or HPV16 VLPs alone induced T helper 1 (Th1)-biased immune responses. Analysis of transcriptional responses of murine BMDCs by microarray suggested that alpha/beta interferon (IFN-alpha/beta) transcripts and numerous proinflammatory cytokines and chemokines are up regulated in response to HPV16 VLPs. Indeed, the induction of IFN-alpha, IFN-gamma, and interleukin-12 (IL-12) production by BMDCs after stimulation with HPV16 VLPs was demonstrated by quantitative enzyme-linked immunosorbent assay. Many microbial products that induce proinflammatory responses are recognized via Toll-like receptor (TLR) signaling through the key adaptor protein MyD88 and activation of NF-kappaB, nuclear factor of activated T cells (NF-AT), and activating protein 1 (AP-1). Reporter assays indicated that HPV16 VLPs activated NF-kappaB-, NF-AT-, and AP-1-dependent transcription in the RAW264.7 macrophage cell line. Knockdown of MyD88 transcripts by small interfering RNA in the RAW264.7 macrophage cell line inhibited the activation of NF-kappaB-, NF-AT- and AP-1-dependent transcription by HPV16 VLP. Furthermore, MyD88(-/-) BMDCs failed to up regulate IL-12 and IFN-alpha and -gamma in response to HPV16 VLPs. Finally, Th1-biased immune responses to HPV16 VLPs are dramatically impaired in MyD88 and IFN-alpha/beta receptor-deficient mice. This implicates TLR recognition as central to immune recognition of HPV16 L1 VLPs.

Human papillomavirus type-16 virus-like particles activate complementary defense responses in key dendritic cell subpopulations.

Human papillomavirus type-16 (HPV16) L1 virus-like particles (VLPs) activate dendritic cells (DCs) and induce protective immunity. In this study, we demonstrate, using global gene expression analysis, that HPV16 VLPs produce quite distinct innate responses in murine splenic DC subpopulations. While HPV16 VLPs increase transcription of IFN-gamma and numerous Th1-related cytokines and chemokines in CD8alpha(+)CD11c(+) DCs, CD4(+)CD11c(+) DCs up-regulate only type I IFN and a different set of Th2-associated cytokines and chemokines. Type I IFN, but not IFN-gamma, potentiates humoral immunity, notably production of VLP-specific IgG2a. However, HPV16 VLP-stimulated IL-12 production by CD8alpha(+)CD11c(+) DCs is augmented by autocrine IFN-gamma signaling. Thus, before adaptive immunity, HPV16 VLPs signal complementary defense responses in key DC subpopulations, indicating specialized DC lineages with predetermined polarization.