Establishing a Proteomics-Based Monocyte Assay To Assess Differential Innate Immune Activation Responses

Innate
immune cells are complex systems that can be simultaneously
activated in a variety of ways. Common methods currently used to estimate
the response of innate immune cells to stimuli are usually biased
toward a single mode of activation. The aim of this study was to assess
the possibility of designing an assay based on unbiased proteome analysis
that would be capable of predicting the complex response of the innate
immune system to various challenges. Monocytes were used as representative
cells of the innate immune system. The underlying hypothesis was that
their proteome response to different activating molecules would reflect
the immunogenicity of these molecules. To identify the main modes
of response, we treated the human monocytic THP-1 cell line with nine
different stimuli. Differentiation and activation were determined
to be the two major modes of monocyte response, with PMA causing the
strongest differentiation and Pam3CSK4 causing the strongest proinflammatory
activation. The established assay was applied to characterize the
monocyte response to epidermal growth factor peptide containing isoaspartate,
which induced differentiation but not proinflammatory activation.
Because of its versatility, robustness, and specificity, this new
assay is likely to find a niche among the more established immunological
methods.