‘Actin-reactive’ discriminated from ‘non-actin-reactive’ smooth muscle autoantibody by immunofluorescence reactivity with rat epithelial cell line

SummaryAimsTo compare smooth muscle antibody (SMA) patterns in tissue sections with patterns in an immunofluorescence assay (IFA) using a rat intestinal epithelial cell line and results from an F-actin IgG ELISA.MethodsSMA positive sera (n = 188) were classified by immunofluorescence staining of rodent kidney, stomach and liver sections as SMA-T (tubules) (n = 124) or SMA-V (vessels) (n = 64). The F-actin pattern on the rat epithelial cell line was identified by immunofluorescence staining of actin cables that was confirmed by dual immunofluorescence co-localisation with phalloidin.ResultsOf 124 SMA-T positive sera, 123 reacted with the epithelial cell line and 120 with F-actin by ELISA, giving sensitivity for detection of anti-F-actin antibody of 99% and 97%, respectively. Of 64 SMA-V positive sera, four reacted with the epithelial cell line (6%) and 41 with F-actin by ELISA (64%). Tests of 493 normal blood donors and 100 disease controls yielded specificities of 584/593 (98.5%) and 562/593 (94.8%) for the cell line IFA and F-actin ELISA, respectively.ConclusionsThe rat epithelial cell line IFA is a robust diagnostic assay for anti-F-actin antibody that can either replace the routine screening for actin-reactive SMA-T antibody in tissue sections or be used as a confirmatory assay for anti-F-actin antibody after screening by F-actin ELISA or on rodent tissue sections by IFA.