Non-heat inactivated autologous serum increases accuracy of in vitro CFSE lymphocyte proliferation test (LPT) for nickel.

Background: Skin patch testing is still seen as the gold standard for the diagnosis of allergic hypersensitivity. For several metals and for patients with a suspected adverse reaction to their medical device implant material, patch testing can be unreliable. The current alternative to metal allergy patch testing is the in vitro lymphocyte proliferation test (LPT) using tritiated thymidine. This method is well-established but requires handling of radioactive material, often uses heat-inactivated allogenic human pooled serum and cannot determine T cell subsets.

Objective: To develop a radioactive free LPT by using carboxyfluorescein succinimidyl ester (CFSE) and to evaluate the influence of serum source (heat-inactivated human pooled serum [HI HPS] vs autologous serum) on the sensitivity and specificity of the nickel-specific LPT.

Methods: Peripheral blood mononuclear cells derived from nickel-allergic patients and healthy controls were collected, labelled with CFSE and cultured in medium containing 10% HI HPS or 10% autologous serum with or without additional T cell skewing cytokine cocktails (Th1: IL-7/IL-12, Th2: IL-7/IL-4 or Th17: IL-7/IL-23/IL-1β) in the absence or presence of NiSO . The stimulation index (SI) was calculated as the ratio of divided cells, that is the percentage of CFSE CD3 CD4 T-lymphocytes upon nickel stimulation compared to the percentage of CFSE CD3 CD4 T-lymphocytes without antigen. These results were compared with the history of Ni allergy, patch test results and the MELISA test.

Results: Autologous serum positively influenced Ni-specific proliferation while HI HPS negatively influenced Ni-specific proliferation. The test protocol analysing CD4 cells and autologous serum without skewing cytokines scored the best diagnostic values (sensitivity 95%; specificity 93%; and overall accuracy 94%) compared to the parallel test using HI HPS (accuracy 60%). Cytokine supplements did not further improve the test protocol which used autologous serum. The protocol using HI HPS could be further improved by addition of the cytokine skewing cocktails.

Conclusions: Here, we describe an optimized and highly accurate flow cytometric LPT which comprises of CFSE-labelled cells cultured in autologous serum (not heat inactivated) and without the presence of T cell skewing cytokines.

Clinical Relevance: The sensitivity and specificity of LPT is enhanced, compared to HI HPS, when autologous serum without skewing cytokines is used.