Interleukin-6 transcripts up-regulation in lymph nodes from unicentric and multicentric Castleman disease.

Introduction: Castleman disease (CD) represents a spectrum of heterogeneous lymphoproliferative disorders sharing peculiar histopathological features, clinically subdivided into unicentric CD (UCD) and multicentric CD (MCD) and presenting with variable inflammatory symptoms. Interleukin (IL)-6 and other cytokines play a major role in mediating CD inflammatory manifestations. Although the local microenvironment seems to be among the major sources of hypercytokinemia, the precise cellular origin of IL-6 production in CD is still debated.

Methods: A series of five nodal CD of different subtypes (one UCD, two idiopathic MCDs [iMCDs], one HIV-negative human herpesvirus 8 (HHV8)-associated MCD, and one HIV-positive HHV8-associated MCD) and a non-CD reactive control were tested using RNAscope analysis and a dual in situ hybridization (ISH)/immunohistochemistry technique, in order to quantify IL-6 expression and its spatial distribution. Quantitative analyses of in situ mRNA were performed on digitalized slides using the HISTOQUANT software (3DHISTECH) and differences between cases were evaluated by the Kruskal-Wallis test.

Results: RNA-ISH documented increased expression in all CD lymph nodes, independently from clinical and pathological subtypes, however, the highest levels were found in HHV8+ cases and statistically significant differences in IL-6 expression were found only between HHV8+ MCD and control case. Dual RNA-ISH for coupled with immunohistochemistry analysis showed that IL-6 was overexpressed in CD31-positive endothelial cells in 5/5 CD tested cases but not in the control case.

Conclusion: Our findings suggest that nodal IL-6 expression seems to be significantly upregulated in HHV8+ MCD, but a trend toward increased nodal IL-6 expression was noticed also in UCD and iMCD-not otherwise specified. CD31+ endothelial cells probably represent one of the major sources of IL-6 production in the nodal microenvironment.