Hydrophobicity drives receptor-mediated uptake of heat-processed proteins by THP-1 macrophages and dendritic cells, but not cytokine responses

Impact of processing on immunogenicity of food proteins has clearly been demonstrated, but the underlying mechanisms are still unclear. In our previous study, the uptake of the cows milk protein {beta}-lactoglobulin (BLG) by THP-1 macrophages varied after applying different processing methods and was positively correlated with hydrophobicity and aggregation. Here we applied the same 3 processing methods: wet heating (60 {degrees}C) and low- or high-temperature (50 {degrees}C or 130 {degrees}C, respectively) dry heating in absence or presence of reducing sugars (i.e. glucose, lactose or galacto-oligosaccharide) to lysozyme and thyroglobulin, which have different pI or molecular weight compared to BLG, respectively. Uptake of the soluble fraction was tested in two types of, genetically homogeneous, antigen-presenting cells (macrophages and dendritic cells derived from THP-1 monocytes). This revealed a strong correlation between the uptake of the different protein samples by macrophages and dendritic cells, and confirmed the key role of hydrophobicity, over aggregation, in determining the uptake. Several uptake routes were shown to contribute to the uptake of BLG by macrophages. However, cytokine responses following exposure of macrophages to BLG samples were not related to the levels of uptake. Heat-treatment-mediated increases in uptake did thus not induce a response in our read-out systems. Together, our results demonstrate that heat-treatment-induced increased hydrophobicity is the prime driving factor in uptake, but not in cytokine production, by THP-1 macrophages.