Differences in Cytokine Expression at Baseline and in Response to Mineral Stimulation by Peripheral Blood Mononuclear Cells from Podoconiosis Cases and Healthy Control Individuals

Epidemiological, histological, and immunogenetic studies suggest that podoconiosis (a non-infectious tropical lymphoedema affecting approximately 4 million people globally) is an HLA class II-associated inflammatory condition that develops in response to an unknown trigger found in volcanic red clay soils. Silicate particles of the kaolinite and aluminum types have been identified in femoral lymph node biopsy samples from endemic area residents, suggesting a possible role in the pathogenesis of podoconiosis. We measured in vitro peripheral blood mononuclear cell cytokine responses (<i>TNF-α</i>, <i>IL-1β</i>, and <i>IFN-γ</i>) to stimulation with the minerals kaolinite, chlorite, and beryllium sulfate (all at 100 µM) using ELISA. Real time PCR was used to measure gene expression of signature cytokines in fresh whole blood, comparing podoconiosis patients and endemic healthy controls. Our results showed that the levels of <i>TNF-α</i> and <i>IL-1β</i> from in vitro cell cultures were significantly higher in unstimulated samples from patients compared to controls (<i>p</i> = 0.04 and <i>p</i> = 0.005, respectively). The minerals kaolinite and chlorite induced two and three-fold higher levels of <i>IL-1β</i> following 24 h of stimulation in healthy controls compared to patients, respectively. We did not find significant differences in mRNA expression of the cytokine genes assayed, though a slight fold increment in <i>IL-1β</i> and <i>TGF-β</i> was observed. In conclusion, our data suggest that the immune system is in a state of persistent activation in vivo in podoconiosis patients, and additional studies of immune regulation and exhaustion are needed to further characterize immune dysfunction in the pathogenesis of the disease. A better understanding of the underlying processes could lead to the development of a 'biosignature' detectable in the early reversible stages that could ultimately contribute to the elimination of this preventable, disabling, neglected tropical disease.