Cobalt-specific T lymphocytes in synovial tissue after an allergic reaction to a cobalt alloy joint prosthesis.

Metals such as cobalt and nickel are common contact allergens. We studied the mechanisms underlying an allergic reaction with marked synovial inflammation in a patient with a cobalt alloy arthroplasty. After removing the joint prosthesis the adjacent synovial tissue was examined for cobalt-specific T lymphocytes. Synovial membrane mononuclear cells were expanded in interleukin 2 and cloned using a representative cloning protocol. T cell clones were tested for their proliferative response to cobalt and further characterized with regard to cytokine secretion, phenotype, and HLA restriction. Additionally, synovial fibroblasts were tested for their function as antigen presenting cells (APC). Almost 30% of the T cell clones reacted to cobalt, but not to the control nickel. All these T cell clones were CD4 positive. The cobalt induced proliferative response could be blocked by anticlass II antibodies. Also, synovial fibroblasts expressing class II molecules induced by interferon-gamma were able to serve as APC. However, when testing a panel of APC of HLA class II mismatched donors, no requirement for a certain HLA class II molecule could be defined. Further studies are necessary to determine mechanisms of presentation and recognition of cobalt by T lymphocytes, a prerequisite for improved prevention and treatment of metal induced allergic reactions.