CD21 and CD23 expression differences in small B-cell lymphomas: comparative analysis in follicular dendritic cells and tumor cells

Objective: Different follicular dendritic cells (FDCs) meshwork patterns were observed in small B-cell lymphomas (SBL) specimens. However, the accurate CD21 and CD23 expression differences in both follicular dendritic cells (FDCs) and tumor cells in SBLs were not sufficiently investigated. Methods: CD21 and CD23 immunostainings were performed on our surgically resected SBL samples to compare their differences in detecting of FDC meshwork immunoarchitectural patterns (FDC patterns), three parameters were introduced for accurate description and comparison of FDC patterns: including the ratio of FDC meshwork outlined area to total tumor area (ROT), staining intensity, and major patterns type (I, expanded follicles with sharp margin; II, contracted follicles with moth-eaten margin; III, ill-defined expanded nodules; IV, absent). The exact expression frequencies of CD21 and CD23 in all SBL groups was also evaluated and compared using double immunohistochemistry (D-IHC). Results: 103 nodal SBL cases, including 32 follicular lymphoma (FL), 28 marginal zone lymphoma (MZL), 23 mantle cell lymphoma (MCL), and 20 chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) cases were examined for more accurate data of FDC pattern parameters, including the mean of ROTs, the percentages of cases exhibiting strongly positive staining and the most common distribution patterns. For CD21 and CD23 they were (46.3% and 39.2%), (81.3% and 78.1%) and (type I, accounting for 93.8% and 81.3%) of all cases respectively in the FL group, (21.4% and 16.8%), (56.5% and 82.6%) and (type III, accounting for 47.8% and 52.2%) in the MCL group, (23.7% and 28.6%), (71.4% and 92.8%) and (type II, accounting for 50% and 67.9%) respectively in the MZL group, and (2.2% and 0.3%), (20% and 5%) and (type IV, accounting for 60% and 95% cases) respectively in the CLL/SLL group. No significant difference was seen in CD21 and CD23 labeling of the FDC pattern parameters. Based on the results of D-IHC, CD21 was detected in 28.1%, 60.9%, 60.7% and 55% of the tumor cells from the FL, MCL, MZL and CLL/SLL samples, respectively, and CD23 was detected in 34.4%, 21.7%, 28.6% and 95% of the respective samples. Conclusion: The most common distribution pattern of FDC patterns was identical between these two markers. Both displayed pattern I in FL, III in MCL, II in MZL and IV in CLL/SLL. The D-IHC results showed that both CD21 and CD23 were expressed in partial cases from each SBL subtype. CD21 expression was much less abundant in FL tumor cells, and CD23 expression was much more abundant in CLL/SLL tumor cells.