Which substrate would show cytoplasmic speckling in a specimen with a perinuclear staining pattern during an ANCA immunofluorescent assay?

Cytoplasmic speckling in a specimen with a perinuclear staining pattern during an ANCA (antineutrophil cytoplasmic antibody) immunofluorescent assay is typically associated with the use of formalin-fixed neutrophils. Formalin fixation preserves the cellular architecture and allows for the detection of certain antigenic structures within the neutrophils, leading to the distinctive cytoplasmic speckling that can be observed.

In this context, formalin-fixed neutrophils reveal the presence of specific proteins or epitopes that react with ANCA, resulting in the characteristic staining patterns, including perinuclear and cytoplasmic speckling. The fixation process stabilizes proteins, making them available for antibody binding during the immunofluorescent assay. This contrasts with unfixed neutrophils, which might not exhibit the same pattern due to the loss of protein integrity or changes in antigenicity after lysis or fixation.

HEp-2 cells are commonly used as substrates for antinuclear antibodies (ANA) testing and may show different staining patterns consistent with nuclear antigen detection, rather than the cytoplasmic speckling observed in ANCA assays. Similarly, rabbit kidney tissue might have relevant antigens for different autoimmune ser