Engagement of the T cell antigen receptor (TCR) rapidly induces multiple signal transduction pathways, including ERK activation. Here, we report a critical role for ERK at a late stage of T cell activation. Inhibition of the ERK pathway 2-6 h after the start of TCR stimulation significantly impaired interleukin-2 (IL-2) production, whereas the same treatment during the first 2 h had no effect. ERK inhibition significantly impaired nuclear translocation of c-Rel with a minimum reduction of NF-AT activity. Requirement for sustained ERK activation was also confirmed using primary T cells. To induce sustained activation of ERK, T cells required continuous engagement of TCR. Stimulation of T cells with soluble anti-TCR antibody resulted in activation of ERK lasting for 60 min, but failed to induce IL-2 production. In contrast, plate-bound anti-TCR antibody activated ERK over 4 h and induced IL-2. Furthermore, T cells treated with soluble anti-TCR antibody produced IL-2 when phorbol 12-myristate 13-acetate, which activates ERK, was present in the culture medium 2-6 h after the start of stimulation. Together, the data demonstrate the presence of a novel activation process following TCR stimulation that requires ERK-dependent regulation of c-Rel, a member of the NF-B family.

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Background Periprosthetic joint infection (PJI) is one of the most devastating complications of total joint arthroplasty. Given the mortality and morbidity associated with PJI and the challenges in treating it, there has been increased interest in risk factors that can be modified before surgery. In this study, we used a novel mouse model to consider the role of the gut microbiome as a risk factor for PJI. Questions/purposes (1) Does the state of the gut microbiota before surgery influence the likelihood of developing an established infection in a mouse model of PJI? (2) How does the state of the gut microbiota before surgery influence the local and systemic response to the presence of an established infection in a mouse model of PJI? Methods Male C57Bl/6 mice were divided into two groups: those with modified microbiome ∆microbiome (n = 40) and untreated mice (n = 42). In ∆microbiome mice, the gut flora were modified using oral neomycin and ampicillin from 4 weeks to 16 weeks of age. Mice received a titanium tibial implant to mimic a joint implant and a local inoculation of Staphylococcus aureus in the synovial space (102 colony forming units [CFUs]). The proportion of animals developing an established infection in each group was determined by CFU count. The local and systemic response to established infection was determined using CFU counts in surrounding joint tissues, analysis of gait, radiographs, body weight, serum markers of inflammation, and immune cell profiles and was compared with animals that received the inoculation but resisted infection. Results A greater proportion of animals with disrupted gut microbiota had infection (29 of 40 [73%]) than did untreated animals (21 of 42 [50%]; odds ratio, 2.63, 95% CI, 1.04–6.61; p = 0.035). The immune response to established infection in mice with altered microbiota was muted; serum amyloid A, a marker of systemic infection in mice, was greater than in mice with disrupted gut microbiota with infection (689 µg/dL; range, 68–2437 µg/dL, p < 0.05); infection associated increases in monocytes and neutrophils in the spleen and local lymph node in untreated mice but not were not observed in mice with disrupted gut microbiota. Conclusions The findings from this in vivo mouse model suggest that the gut microbiota may influence susceptibility to PJI. Clinical Relevance These preclinical findings support the idea that the state of the gut microbiome before surgery may influence the development of PJI and justify further preclinical and clinical studies to develop appropriate microbiome-based interventions.