The perspectives of regenerative medicine are still severely hampered by the host response to biomaterial implantation, despite the robustness of technologies that hold the promise to recover the functionality of damaged organs and tissues. In this scenario, the cellular and molecular events that decide on implant success and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. To avoid adverse events, rather than the use of inert scaffolds, current state of the art points to the use of immunomodulatory biomaterials and their knowledge-based use to reduce neutrophil activation, and optimize M1 to M2 macrophage polarization, Th1 to Th2 lymphocyte switch, and Treg induction. Despite the fact that the field is still evolving and much remains to be accomplished, recent research breakthroughs have provided a broader insight on the correct choice of biomaterial physicochemical modifications to tune the reaction of the host immune system to implanted biomaterial and to favor integration and healing.

In adult healthy cartilage, chondrocytes are in a quiescent phase characterized by a fine balance between anabolic and catabolic activities. In ageing, degenerative joint diseases and traumatic injuries of cartilage, a loss of homeostatic conditions and an up-regulation of catabolic pathways occur. Since cartilage differentiation and maintenance of homeostasis are finely tuned by a complex network of signaling molecules and biophysical factors, shedding light on these mechanisms appears to be extremely relevant for both the identification of pathogenic key factors, as specific therapeutic targets, and the development of biological approaches for cartilage regeneration. This review will focus on the main signaling pathways that can activate cellular and molecular processes, regulating the functional behavior of cartilage in both physiological and pathological conditions. These networks may be relevant in the crosstalk among joint compartments and increased knowledge in this field may lead to the development of more effective strategies for inducing cartilage repair.

Objective To evaluate the sites of expression of interleukin‐1β (IL‐1β), tumor necrosis factor α (TNFα), and inducible nitric oxide synthase (iNOS) in patients with inflammatory and degenerative joint diseases. Methods Cytokines and iNOS were detected by immunohistochemistry analysis of synovial and cartilage biopsy specimens obtained at knee arthroscopy in patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA), osteoarthritis (OA), and traumatic knee arthritis. Cytokine and iNOS expression was quantified using computerized image analysis. Results IL‐1β, TNFα, and iNOS were highly expressed by synovial cells (lining layer cells, infiltrating leukocytes, endothelial cells) from patients with inflammatory arthritides and significantly less by synovial cells from patients with OA and traumatic arthritis. In contrast, the latter patients showed high chondrocyte expression of cytokines and iNOS while RA and PsA patients had only minor chondrocyte positivity. In both joint compartments, IL‐1β expression, TNFα expression, and iNOS expression were strongly correlated. Conclusion The enhanced and coordinated expression of IL‐1β, TNFα, and iNOS by chondrocytes strongly supports the hypothesis that chondrocytes are the major site of production of mediators of inflammation in human OA, thus playing a primary role in the pathogenesis of this disease.

Objective. To determine laboratory parameters that may be useful in identifying polymyalgia rheumatica (PMR) patients who require long-term corticosteroid therapy. Methods. A prospective followup study of 94 consecutive untreated patients with PMR were assessed for relapse/recurrence for a mean of 39 months. This cohort represented all the patients diagnosed over a 4-year period in 2 Italian secondary referral centers. Patients were monitored for clinical signs and symptoms, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and serum interleukin-6 (IL-6). IL-6 levels were also measured in 43 controls matched to the patients for age and sex. Results. The ESR was elevated in 91.5% of the patients prior to therapy initiation, as were CRP in 98.9% and serum IL-6 in 92.6%. Forty-seven (50.0%) patients had at least 1 relapse/recurrence during the followup period and 24 (25.5%) had at least 2. After 4 weeks of prednisone therapy, ESR was elevated in 13.2% patients, CRP in 41.9%, and serum IL-6 in 37.2%. IL-6 levels remained persistently elevated in 9.9% and CRP in 8.7% of patients during the first year of followup, whereas no patient had persistently elevated ESR. Persistently elevated CRP and IL-6 levels were significantly associated with an increased risk of relapse/recurrence. In particular, patients with persistently elevated levels of IL-6 during the first year of therapy had the highest relative risk. Conclusion. Despite the control of clinical symptoms, corticosteroids do not adequately control the inflammatory process in a subset of patients with PMR who have persistently elevated levels of CRP and IL-6 and who have a higher risk of relapsing.