Immune regulation by CD55 in chronic beryllium disease.

CD55 is an immune regulator that inhibits T-cell activation and also binds to CD97, a molecule involved in immune cell migration and signaling. While CD55 expression is reduced in chronic beryllium disease (CBD), its functional role in disease pathogenesis remains unclear. We hypothesized that CD55 downregulation in peripheral blood mononuclear cells (PBMCs) contributes to heightened beryllium (Be)-specific immune responses in CBD. To test this, we characterized CD55 expression and function in PBMCs from patients with CBD and individuals with beryllium sensitization (BeS), as well as in a human Be-specific T-cell model. CD55, soluble CD55 (sCD55), and CD97 mRNA expression was quantified by qRT-PCR in PBMCs from CBD (n = 25), BeS (n = 36), and control (n = 7) participants. BeSO4 (beryllium sulfate) stimulation was used to assess CD55, STAT1, JAK2, and TNF-α expression over time in CBD PBMCs (n = 8). Serum sCD55 was measured by ELISA in an independent cohort. Functional studies using anti-CD55 neutralizing antibodies and the JAK2 inhibitor TG101348 evaluated effects on TNF-α production and lymphocyte proliferation (beryllium lymphocyte proliferation test [BeLPT]) in PBMCs, and IL-2 production in a Jurkat-Be cell model. CD55, sCD55, and CD97 were significantly downregulated in CBD PBMCs compared to BeS (P < .001). Serum sCD55 was also reduced in CBD (P < .05). BeSO4 stimulation further downregulated CD55 and upregulated STAT1. CD55 blockade increased TNF-α production and BeLPT responses in CBD (P < .001) and BeS (P < .05); these effects were reversed by JAK2 inhibition. In the Be-cell model, CD55 inhibition enhanced IL-2 production (P < .01), attenuated by JAK2 blockade. These findings suggest that CD55 downregulation amplifies Be-induced immune responses in CBD via JAK2/STAT1 signaling.