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 t he mechanisms under lying an allergic reaction with marked synovial inflamm ation in a patient with a cobalt alloy arthroplasty. After removing the joi nt prosthesis the adjacent synovial tissue was examined for cobalt-specific T lymphocytes. Synovial membrane mononuclear cells were expanded in interl eukin 2 and cloned using a representative cloning protocol. T cell clones w ere tested for their proliferative response to cobalt and further character ized with regard to cytokine secretion, phenotype, and HLA restriction. Add itionally. synovial fibroblasts were tested for their function as antigen p resenting cells (APC). Almost 30% of the T cell clones reacted to cobalt, b ut not to the control nickel. All these T cell clones were CD4 positive. Th e cobalt induced proliferative response could be blocked by anti class II a ntibodies. Also, synovial fibroblasts expressing class II molecules induced by interferon-gamma were able to serve as APC, However, when testing a pan el of APC of HLA class II mismatched donors, no requirement for a certain H LA class II molecule could be defined. Further studies are necessary to det ermine mechanisms of presentation and recognition of cobalt by T lymphocyte s, a prerequisite for improved prevention and treatment of metal induced al lergic reactions.