IFN-can skew human Ab responses toward the IgG1 opsonizing and complement-fixing Ig subclass and IL-4 toward the allergy-related IgG4 and IgE subclasses (21). is perturbed in RA and suggest that increased EBV-specific effector T cell and Ab responses are driven by an elevated EBV load in RA. Rheumatoid arthritis (RA)5 is a chronic inflammatory disease with an unknown etiology. Data from clinical trials as well as from animal models demonstrate a role for both T and B lymphocytes in RA pathogenesis (1, 2) and certain HLA-DR class II alleles; D2PM hydrochloride for example, HLA-DRB1*01 and HLA-DRB1*0401 are the strongest risk-conferring genes (3). It is, however, unclear to date if pathogenic T cells in RA predominantly recognize self or pathogen-derived Ags. The fact that concordance rates for RA are only between 15 and 30% among monozygotic twins strongly argues for environmental factors, such as pathogens that trigger or perpetuate the disease (4). EBV has been suspected for more than 25 years to be involved in RA pathogenesis (5C9). EBV is a gammaherpesvirus that infects 90% of the human adult population. After primary infection in childhood or adolescence, EBV persists life-long in B lymphocytes. In latently infected B cells, only some viral proteins are expressed and confer D2PM hydrochloride resistance to apoptosis, possibly preventing activation-induced cell death of autoreactive B cells. The frequency D2PM hydrochloride of EBV-infected B cells in the blood is low (0.5C50 per million) and stable over time. Periodically, activation of infected B cells by Ag receptor triggering leads to reactivation of EBV into lytic cycle for transmission of infectious virus in the saliva of healthy virus carriers. Strong T cell responses against lytic and latent EBV Ags can be detected in healthy asymptomatic carriers and are critically important for the control of latent infection. CD4+ Th cell responses against EBV nuclear Ag 1 (EBNA1) can be consistently detected in healthy virus carriers. EBNA1-specific T cells produce IFN-= 14/25) with those not receiving immunosuppressive or immunomodulatory therapy (= 11/25) compared with healthy donors and noted no significant differences in any parameter tested. Age- and sex-matched healthy donors were recruited from a family physicians private practice. We excluded patients with autoimmune or other chronic inflammatory disease, metabolic disorders, and a recent history of infection. Not all patients and controls were included in every analysis; rather, subsets of both groups were chosen as indicated in the results section Id1 and figure legends. Demographic and clinical characteristics are given in Table I. The study was approved by the local Institutional Review Board, and all subjects provided informed consent. Table I Patients and healthy blood donors BL21 (DE3) pLysS cells. Production was D2PM hydrochloride induced with 1 mM isopropyl enterotoxin B (SEB; 1.5 (25723.11), and CD45RO (UCHL-1; all from BD Pharmingen) for 15 min at room temperature. After two washes, cells were resuspended in 200 producing T cells were calculated using FlowJo software (Tree Star). According to criteria previously used in ELISPOT analyses (25), a positive response required a frequency at least 2-fold above background (no Ag) and at least 10 IFN-= 2 is the EBV is the EBV is the bcl-2 copy number. All samples were tested in at least duplicate, and the mean results were determined. Statistical analysis Statistics were performed using commercial software (Prism 4, GraphPad Software). Comparisons between RA patients and healthy donors were based on the nonparametric Mann-Whitney test. Categorical differences between the two cohorts were analyzed by Fishers exact test. For correlation analyses between clinical disease parameters and T cell responses, we used the nonparametric Spearman correlation. Results Increased EBV-specific IgG titer and frequent IgG recognition of EBV-encoded early Ags in RA First, we evaluated.