Effective antiviral immunity depends on the ability of infected cells or cells triggered with virus-derived nucleic acids to produce type I interferon (IFN), which activates transcription of numerous antiviral genes. However, disproportionately strong or chronic IFN expression is a common cause of inflammatory and autoimmune diseases. We describe an epigenetic mechanism that determines cell type–specific differences in IFN and IFN-stimulated gene (ISG) expression in response to exogenous signals. We identify di-methylation of histone H3 at lysine 9 (H3K9me2) as a suppressor of IFN and IFN-inducible antiviral gene expression. We show that levels of H3K9me2 at IFN and ISG correlate inversely with the scope and amplitude of IFN and ISG expression in fibroblasts and dendritic cells. Accordingly, genetic ablation or pharmacological inactivation of lysine methyltransferase G9a, which is essential for the generation of H3K9me2, resulted in phenotypic conversion of fibroblasts into highly potent IFN-producing cells and rendered these cells resistant to pathogenic RNA viruses. In summary, our studies implicate H3K9me2 and enzymes controlling its abundance as key regulators of innate antiviral immunity.

Sarcoidosis is a disease of unknown etiology characterized by noncaseating epithelioid granulomas, oligoclonal CD4 + T cell infiltrates, and immune complex formation. To identify pathogenic antigens relevant to immune-mediated granulomatous inflammation in sarcoidosis, we used a limited proteomics approach to detect tissue antigens that were poorly soluble in neutral detergent and resistant to protease digestion, consistent with the known biochemical properties of granuloma-inducing sarcoidosis tissue extracts. Tissue antigens with these characteristics were detected with immunoglobulin (Ig)G or F(ab′) 2 fragments from the sera of sarcoidosis patients in 9 of 12 (75%) sarcoidosis tissues (150–160, 80, or 60–64 kD) but only 3 of 22 (14%) control tissues (all 62–64 kD; P = 0.0006). Matrix-assisted laser desorption/ionization time of flight mass spectrometry identified Mycobacterium tuberculosis catalase–peroxidase (mKatG) as one of these tissue antigens. Protein immunoblotting using anti-mKatG monoclonal antibodies independently confirmed the presence of mKatG in 5 of 9 (55%) sarcoidosis tissues but in none of 14 control tissues (P = 0.0037). IgG antibodies to recombinant mKatG were detected in the sera of 12 of 25 (48%) sarcoidosis patients compared with 0 of 11 (0%) purified protein derivative (PPD) − (P = 0.0059) and 4 of 10 (40%) PPD + (P = 0.7233) control subjects, suggesting that remnant mycobacterial catalase–peroxidase is one target of the adaptive immune response driving granulomatous inflammation in sarcoidosis.

The idea that stem cells oscillate between a state of activity and dormancy, thereby giving rise to differentiating progeny either randomly or in orderly clonal succession, has important implications for understanding normal hematopoiesis and blood cell dyscrasias. The degree of clonal stability in individuals also has practical implications for the evaluation of clonal lymphomyeloproliferative diseases. To evaluate the clonality pattern of the different types of blood cells as a function of time we have validated the applicability, sensitivity, and reproducibility of a thermostable ligase reaction to detect transcripts of the G6PD allele on the active X-chromosome in normal heterozygous females. While the ratio of the two X-chromosome-derived allelic transcripts varied widely among hemopoietic tissues in a given individual, this allelic ratio was virtually identical in all types of mature myeloid and lymphoid cells. Longitudinal studies indicated constancy of the G6PD allelic ratio in blood cells over a 912-d period of observation in healthy females. The individual variability observed in this allelic ratio suggests that the progeny of a relatively small number of original embryonic hemopoietic stem cells, approximately eight, contribute to the sustained production of all types of blood cells in healthy individuals.

Certain aspects of the phenomenon of IgE class-restricted tolerance induced in mice by neonatal treatment with monoclonal IgE, either in soluble form or coupled to syngeneic spleen cells, were examined. The present studies document that this tolerance results from exposure to IgE molecules, irrespective of their antigen specificity, and the resulting effects are polyclonal in nature since IgE responses directed against antigenic determinants unrelated to the tolerance-inducing IgE molecules are affected. Moreover, such findings indicate that the molecular subregion(s) responsible for inducing IgE class-restricted tolerance resides in the epsilon heavy chain constant region domain(s) of IgE. When soluble IgE is employed, tolerance induction results from neonatal treatment with doses as low as 2.5 micrograms per injection per mouse; cell-bound IgE is considerably more potent, in terms of total dose required, since tolerance results from treatment with as few as 1 X 10(6) cells per injection (per mouse), equivalent to an absolute quantity of 0.2 ng of IgE per injection. This long-term class-specific tolerance appears to be a unique feature of the IgE antibody system, since treatment of mice with monoclonal antibodies of the IgA, IgG1, or IgG2b isotypes, either in soluble or cell-bound form, does not perturb antibody responses of their corresponding isotypes or in the IgE class. By analyzing the lymphoid cells of IgE-tolerant mice after they reached adulthood, the following observations were made: (a) lymphoid cells from such tolerant mice fail to develop FcR epsilon + cells upon in vitro stimulation with IgE, as is characteristically observed with lymphoid cells from nontolerant mice; and (b) mice rendered tolerant by neonatal treatment with soluble IgE possess IgE class-restricted suppressor T cells, demonstrable in adoptive transfer experiments, whereas no such suppressor cells are evident in mice in which cell-bound IgE was used for neonatal treatment. The latter observations could mean that two different mechanisms underlie the IgE class-restricted tolerance, or both mechanisms operate coordinately to varying degrees depending upon which regimen is used for tolerance induction, as discussed herein.

Induction of IgE class-restricted tolerance was studied in high IgE-responder (BALB/c X SJL)F1 mice, of which the parental BALB/c and SJL mice are high and low IgE-responder mice, respectively. 2,4-Dinitrophenyl (DNP)-specific monoclonal IgE was administered to (BALB/c X SJL)F1 mice neonatally in two forms: soluble IgE at 250 micrograms per injection, or 10-100 ng of IgE coupled to 25-50 X 10(6) syngeneic splenocytes by binding to the chemically reactive hapten trinitrobenzene sulfonate (TNBS) or directly conjugated via a heterobifunctional reagent, N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP). Polyclonal induction of IgE class-restricted tolerance was observed in (BALB/c X SJL)F1 mice, neonatally treated with soluble IgE or IgE-conjugated syngeneic splenocytes. Thus these mice failed to mount IgE antibody responses to either keyhole limpet hemocyanin or ovalbumin challenge, assessed by the passive cutaneous anaphylaxis reaction. The IgG antibody responses to these same antigens, however, were not affected by this treatment. The IgE class-restricted tolerance induced by both forms of IgE persisted up to at least 6 mo with repeated antigenic challenges. IgE coupled to syngeneic cells by TNBS or the SPDP method induced prolonged tolerance up to 9 mo. The induction of polyclonal IgE class-restricted tolerance was achieved only by monoclonal IgE, whereas DNP-specific monoclonal IgG1 plus IgG2b coupled to syngeneic splenocytes by the SPDP method failed to modulate either IgE or IgG antibody responses. In contrast, (BALB/c X A/J)F1 mice, of which both parental strains are high IgE responders, developed IgE class-restricted tolerance upon repeated neonatal injection of soluble IgE, but not IgE-conjugated syngeneic splenocytes, indicating that gene products of the low IgE-responder mice contributed to the effective presentation and/or recognition of epsilon heavy chain of the IgE molecules. Taken collectively, these results demonstrated that non-antigen-specific, isotype-restricted tolerance can be induced in the IgE antibody system. The differential induction of IgE class-restricted tolerance by different forms of tolerogen in the strains studied perhaps distinguishes two underlying cellular mechanisms for IgE class-restricted tolerance.

Group A streptococcal peptidoglycan has previously been shown to be arthritogenic in rats and has been implicated as a structure present in a class of possible etiologic agents for rheumatoid arthritis. The present study reports that conditioned medium from human monocytes, after interaction with cell wall sonicates of four group A streptococcal strains, stimulates the plasminogen activator (PA) activity of nonrheumatoid synovial fibroblasts. Low concentrations of N-acetylmuramyl-L-alanyl-D isoglutamine (muramyl dipeptide) can also generate this synovial activator (SA) activity from human monocytes. Preliminary biochemical data suggest that the SA activity is distinct from interferon-gamma, interleukin 1, and interleukin 2. These results indicate that agents that are arthritogenic in rats can modulate human synovial fibroblast functions via monocytes. The findings are proposed to have possible significance for an understanding of the cellular interactions involved in the formation and function of the rheumatoid pannus, because PA has been invoked as possibly being generally important for the processes of cell migration, tissue remodeling, and inflammation.

Friend murine leukemia virus (FV), isolated from infectious serum of several mouse strains, has been examined for the presence of H-2 antigens. Following banding of the virus on a discontinuous sucrose gradient, pelleting, and disruption with Nonidet P-40 detergent, virus preparations were tested for their capacity to inhibit the lysis of target cells mediated by various anti-H-2K or anti-H-2D antisera. Virus from mice homozygous for the H-2b, H-2d, H-2g H-2k, and H-2ol haplotypes or heterozygous for the H-2g/H-2k, H-2b/H-2d, and H-2b/H-2k haplotypes was used. Of the six H-2D or H-2K alleles examined, the products of only two, H-2Db and H-2Kk were detected. Virus preparations contained no, one, or both antigens, depending on the genotype of the host animal. Control preparations from normal mouse serum and preparations in which the virus had not been disrupted demonstrated no H-2 activity. Furthermore, attempts to neutralize FV spleen focus forming activity with anti-H-2Db or anti-H-2Kk antisera yielded negative results.