Utility of Immunohistochemistry and Immunofluorescence in Determining the Pathogenic Variants of Chronic Granulomatous Disease.

Abstract

Chronic granulomatous disease (CGD) is a primary immunodeficiency disorder of phagocytes due to defects in any of the five subunits of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. An initial diagnosis of CGD is made by flow cytometry-based dihydrorhodamine assay or nitro blue tetrazolium test, which is further confirmed by molecular assays. Expression of five subunits of NADPH oxidase components by either flow cytometric or western blot analysis provides clues toward the potential gene targets which are subsequently confirmed by various genetic assays. Immunohistochemistry (IHC) and immunofluorescence (IF) have never been earlier used to determine the expression of different subunits of NADPH oxidase system. We evaluated the utility of IHC and IF in determining the underlying pathogenic variants of CGD. Twelve genetically confirmed cases of CGD, comprising of biopsy specimens (n = 6), tissue blocks from autopsy cases (n = 3), and cellblocks of cell pellet prepared from peripheral blood (n = 4) were included. IHC for p67phox and p47phox subunits and IF for cytochrome b558 were performed. All 4 cases with pathogenic variation of NCF2 gene showed loss of expression for p67phox subunit. Two cases with pathogenic variation of NCF1 gene showed loss of expression for p47phox subunit. Five cases, except a single case with CYBB gene pathogenic variation, showed loss of expression for cytochrome b558 on IF. Thus, loss of expression consistently matched with the underlying genetic defects assessed by sequencing. Our results confirm our hypothesis that IHC and IF are two rapid, economical, pathologist-friendly techniques providing pertinent information regarding the underlying pathogenic variants and such immuno-analysis can be easily performed on the tissue.