Sandwich ELISAs for soluble immunoglobulin superfamily receptor translocation-associated 2 (IRTA2)/FcRH5 (CD307) proteins in human sera

Background The immunoglobulin superfamily receptor translocation-associated 2 (IRTA2) gene encodes both membrane and secreted forms of the B-cell differentiation antigen (also identified as FcRH5). The membrane form is highly expressed on the surface of hairy cell leukemia (HCL) cells from patients. This study aimed to develop immunoassays for soluble IRTA2/FcRH5 proteins in human serum. Methods Two sandwich ELISAs for soluble IRTA2/FcRH5 were designed using two pairs of monoclonal antibodies specific to four different epitopes on IRTA2/FcRH5. Results In both ELISAs, the lower limit of quantitation for soluble IRTA2/FcRH5 in human serum was 30 ng/mL. The analytical recovery of 0.3-2.1 ng/mL of IRTA2/FcRH5-Fc used as the standard, from a 100-fold dilution of IRTA2/FcRH5-free sera, was 94-106% for ELISA #1 and 89-97% for ELISA #2. Between-assay coefficients of variance were 7.7-17.6% for ELISA #1 and 7.7-32.7% for ELISA #2. Both ELISAs detected soluble IRTA2/FcRH5 protein in sera from normal donors (median 169 ng/mL in ELISA #1 and 146 ng/mL in ELISA #2, n=123) without correlations to gender or age. A marked increase in soluble IRTA2/FcRH5 levels was observed in samples from patients with HCL (medians 719 ng/mL in ELISA #1 and 754 ng/mL in ELISA #2, n=44). Conclusions These ELISAs may be useful for monitoring soluble IRTA2/FcRH5 in HCL and other B-cell malignancies.