Bromelain Activates Murine Macrophages and Natural Killer Cells in Vitro

The innate immune response is critical for effective immunity against most pathogens. In this study, we show that bromelain, a mixture of cysteine proteases, can enhance IFN-γ-mediated nitric oxide and TNFα production by macrophages. Bromelainʹs effect was independent of endotoxin receptor activation and was not caused by direct modulation of IFN-γ receptors. Instead, bromelain either enhanced or acted synergistically with IFN-γ receptor-mediated signals. These effects were seen in both RAW 264.7, a macrophage cell line, and primary macrophage populations. Bromelain also increased IL-2- and IL-12-mediated IFN-γ production by NK cells. These results indicate a potential role for bromelain in the activation of inflammatory responses in situations where they may be deficient, such as may occur in immunocompromised individuals.