Development and Validation of a Fluorescent Microsphere Immunoassay for Soluble CD30 Testing

Testing for soluble CD30 (sCD30), an indicator of Th2 immune response, is a useful prognostic marker in solid organ transplantation, lymphoproliferative disorders, autoimmunity, and various parasitic diseases. In this study we report the development and validation of a fluorescent microsphere immunoassay for the detection of sCD30 in serum, plasma, and culture supernatants. The dynamic range of this assay is 1 to 400 ng/ml, and the rate of recovery of various concentrations of recombinant sCD30 ranges from 97 to 116% (average recovery, 105%). The test showed a high degree of precision in both intra-assay and interassay studies (coefficients of variation, as high as 7% and 8%, respectively), with a sensitivity of 1 ng/ml. The normal reference range calculated for a cohort of 151 healthy individuals was 1 to 29 ng/ml. The clinical usefulness of the sCD30 fluorescent microsphere immunoassay was demonstrated by showing that levels of sCD30 have a positive correlation with specimens containing high titers of anti-double-stranded DNA antibodies and high titers of immunoglobulin G against Leishmania species. Given the multiplexing potential of the sCD30 fluorescent microsphere immunoassay reported in this study, it is expected that testing of sCD30 concentrations along with those of other cytokines will become an important diagnostic tool for selected immunological and inflammatory diseases where Th2-type cytokine responses have been reported.CD30 (TNFRSF 8) is a transmembrane protein, a member of the tumor necrosis factor (TNF) receptor superfamily. It was originally described as a marker for Reed-Sternberg cells (“Ki-1 antigen”) in Hodgkin''s disease (12, 18, 20). CD30 is expressed on CD4⁺ and CD8⁺ T cells that secrete Th-2 type cytokines (8, 17). Signaling through CD30 plays important roles in T- and B-cell growth, differentiation, and function. The soluble form of CD30 (sCD30) is produced after proteolytic cleavage of the membrane-bound CD30 ectodomain by the TNF-α-converting enzyme (9).Numerous studies have reported that circulating levels of sCD30 may represent a biomarker for outcomes in solid-organ transplantation (16, 21). In addition, other studies have reported that levels of sCD30 have important prognostic value for various lymphoproliferative disorders (4, 15, 22), systemic lupus erythematosus (SLE) (5, 7), and leishmaniasis (1, 2). The current method for quantitation of sCD30 is the enzyme-linked immunosorbent assay (ELISA), which has good sensitivity and specificity. However sCD30 production differs greatly between patients, and the dynamic range of ELISAs requires that many samples be diluted and retested. Moreover, ELISA measures only 1 analyte per well, which precludes the testing of multiple analytes in the same test. In this study, we report the development and validation of a fluorescent microsphere immunoassay suitable for multiplexed determination of sCD30 levels, along with those of other cytokines, in serum and plasma specimens and in tissue culture supernatants. We present data showing the positive correlation of sCD30 levels with titers of anti-double-stranded DNA (anti-dsDNA) antibodies in SLE and with immunoglobulin G (IgG) levels in patients with leishmaniasis.