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Although an impact of processing on immunogenicity of food proteins has clearly been demonstrated, the underlying mechanisms are still unclear. We applied 3 different processing methods: wet heating (60 °C) and low- or high-temperature (50 °C or 130 °C, respectively) dry-heating in absence or presence of reducing sugars, to [beta]-lactoglobulin (BLG), lysozyme and thyroglobulin, which represent dietary proteins with different pI or molecular weight. Uptake of the soluble fraction of the samples 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. 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.

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 cow’s milk protein β-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 °C) and low- or high-temperature (50 °C or 130 °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.