CD19 and paracoccidioidomycosis: CD81 is a transmembrane protein and plays an important role in synapse formation between B cells and T cells.17 CD81 can regulate CD19 expression in B lymphocytes and is also involved in cell growth, movement, signal transduction, and the homing of bone marrow cells.18 There is evidence showing that CD81 expression inhibits the migration and invasion of PCM cells, which suggests CD81 as an inhibitor of PCM metastasis.19 The findings of Paiva et al20 also support this conclusion.