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HIV-associated multicentric Castleman disease (HIV-MCD) is a rare lymphoproliferative disorder caused by infection with human herpesvirus-8. The disease follows a relapsing and remitting clinical course, with marked systemic symptoms during an active attack, which can prove fatal. Its incidence is rising, and new data indicate the utility of the anti-CD20 monoclonal antibody rituximab at inducing remissions in both first- and second-line settings, although biomarkers associated with relapse have not been previously identified. In 52 individuals with a histologic diagnosis of HIV-MCD, we performed univariate and multivariate analyses to predict factors associated with an HIV-MCD attack. Although a younger age (< 50 years) was associated with an attack, the strongest association was observed with plasma levels of human herpesvirus-8 DNA. Rising levels predicted an attack (hazard ratio = 2.9; 95% confidence interval, 1.3-6.7), and maintenance therapy with rituximab should be considered in these individuals.

The chemokines CX3CL1/Fractalkine and CXCL16 are expressed as transmembrane molecules and can mediate cell-cell-adhesion. By proteolytic processing, CX3CL1 and CXCL16 are released from the cell surface by proteolytic shedding resulting in the generation of soluble chemoattractants. This ectodomain release is mediated by the alpha-secretase-like activity of the two disintegrins and metalloproteinases ADAM10 and ADAM17. Using CX3CL1 and CXCL16 constructs C-terminally fused to two Z-domains of Protein A (2Z-tag) we detect C-terminal fragments (CTFs) of both chemokines resulting from ADAM10-mediated cleavages at multiple sites as examined by inhibitor studies. Furthermore, inhibitor studies as well as genetic studies using presenilin 1/2-deficient cell lines suggest the involvement of gamma-secretase-but not beta-secretase-like activity in the processing of transmembrane chemokines. The combination of alpha- and gamma-secretase and proteasomal inhibitors points towards a sequential processing of transmembrane chemokines by first ADAM10 and then gamma-secretases and possible further degradation. This proteolytic processing cascade of transmembrane chemokines is similar to that described for Notch and E-cadherin where CTFs generated by gamma-secretase serve as intracellular signal transmitters.