A prerequisite of
proteomics is the ability to quantify many selected proteins simultaneously. Fluorescent sandwich immunoassays on microarrays hold appeal for such studies, since equipment and antibodies are readily available, and assays are simple, scalable and reproducible. To attain adequate sensitivity and specificity, however, a
general method of
immunoassay amplification is required.
Coupling of isothermal rolling circle amplification (RCA) to universal antibodies can be used for this purpose: RCA on a
synthetic DNA circle is initiated by a complementary
oligonucleotide attached to an anti-
biotin antibody; single-stranded RCA product remains attached to the
antibody, and is detected by hybridization of complementary, fluorescent oligonucleotides. 51 cytokines were measured simultaneously on microarrays with
signal amplification by RCA with high specificity, femtomolar sensitivity and 4 log quantitative range. This
cytokine microarray was used to measure
secretion from human Dendritic cells (DCs) induced by
lipopolysaccharide (LPS) or
tumor necrosis factor-alpha (TNF-(alpha). Rapid
secretion of inflammatory cytokines such as MIP-1beta, IL-8, and IP-10 was induced by LPS.
Eotaxin-2 and I-309 were found to be induced by LPS, and MDC, TARC, sIL-6R, and sTNF-RI were found to be induced by TNF-alpha. Since microarrays can accommodate ~1000 sandwich immunoassays of this type, a relatively small number of RCA microarrays appears to offer a tractable approach for proteomic surveys.