Human β‐defensin 2 may inhibit internalisation of bacillus Calmette‐Guérin (BCG) in bladder cancer cells

Objective To investigate whether secretion of human β‐defensin 2 (HBD‐2) is induced by bacillus Calmette‐Guérin (BCG) and to determine whether HBD‐2 affects BCG internalisation in bladder cancer cells. Materials and Methods Reverse transcription‐polymerase chain reaction analysis was used to determine whether HBD‐2 mRNA increases after incubation with BCG. HBD‐2 proteins in 5637 and T24 human bladder cancer cell lines were assayed by enzyme‐linked immunosorbent assay. The internalisation rate was evaluated by double immunofluorescence assay and confocal microscopy to test the optimal dose of HBD‐2 for BCG internalisation. We also investigated the difference in internalisation rates and cell viability between recombinant HBD‐2 protein, anti‐HBD‐2 antibody, and HBD‐2 plus anti‐HBD‐2 antibody pretreatments. Results BCG induced HBD‐2 mRNA expression and HBD‐2 production dose and time‐dependently in bladder cancer cells and affected BCG internalisation. Pretreatment with recombinant HBD‐2 protein lowered internalisation of BCG dose‐dependently. Moreover, anti‐HBD‐2 antibody prevented the effect of HBD‐2 on BCG internalisation in bladder cancer cells. The internalisation rate of BCG pretreated with anti‐HBD‐2 antibody was higher than that in the control in 5637 (P < 0.01) and T24 cells (P < 0.05). The BCG internalisation rate in cells pretreated with anti‐HBD‐2 antibody plus recombinant HBD‐2 protein was higher than that in the control in 5637 (P < 0.01) and T24 cells (P < 0.05). Mycobacterium bovis BCG decreased bladder cancer cell viability, and anti‐HBD‐2 antibody prevented the inhibitory role of HBD‐2 on the anti‐proliferative effects of M. bovis BCG in bladder cancer cells Conclusion Bladder cancer cells produce HBD‐2 when they are infected by BCG to defend themselves against BCG internalisation, which plays an important role during the initiation and propagation of the immunotherapeutic response in bladder cancer cells.