The presence of a CD21+ follicular dendritic cell network distinguishes invasive Quilty lesions from cardiac acute cellular rejection.

ABSTRACT

BACKGROUND: Quilty lesions are a significant source of interobserver variability and overdiagnosis of rejection. These lesions, characterized by a central aggregate of B-cells with a rim of T-cells admixed with capillary-sized blood vessels, exhibit an organization similar to lymphoid tissue. We postulated that this organization is dependent on a follicular dendritic cell (FDC) network and that the presence of such a network would be useful in distinguishing invasive Quilty lesions from acute cellular rejection. METHODS: Thirty-nine lesions of acute cellular rejection [International Society for Heart and Lung Transplantation (ISHLT) grade 1A/1B, n = 7; grade 2, n = 13; grade 3A/3B, n = 18; grade 4, n = 1] and 32 invasive Quilty lesions were collected from our pathology archives. Immunohistochemical staining for CD21 was used to determine the presence of a FDC network. RESULTS: A compact CD21 FDC network was present in 24 of 32 invasive Quilty lesions, and, more significantly, in 23 of 24 invasive Quilty lesions measuring larger than 0.3 mm in greatest dimension. When present, the FDCs were in the center of the lesion and the number of positive cells was proportional to the size of the lesion. A FDC network was completely absent in all but one of the 39 lesions of acute cellular rejection. Review of the H&E material from this single case showed features more consistent with a diagnosis of an invasive Quilty lesion. CONCLUSIONS: The presence of a CD21 FDC network is a reliable diagnostic tool to differentiate invasive Quilty lesions from acute cellular rejection, especially in those lesions (> 0.3 mm) that are most likely to be overdiagnosed as moderate or severe acute cellular rejection (sensitivity 96%, specificity 100%, positive predictive value 100%).