Abstract
There is mounting evidence that the microbiome plays a critical role in training and maturation of the host immune system. Pre-clinical and clinical studies have shown that microbiome perturbation is correlated with sub-optimal host responses to vaccines and cancer immunotherapy. As such, identifying species of commensal bacteria capable of modulating immunological outcomes is of considerable interest. Currently, the lack of reliable primary immune cell-based assays capable of differentiating immuno-modulatory properties of various commensal bacteria is a major limitation. Here, we demonstrate that primary human monocyte-derived dendritic cells (MoDC) are capable of stratifying different strains of live and heat-killed commensal bacteria in an in vitro culture system. Specifically, heat-killed bacterial strains were able to differentially modulate co-stimulation/maturation markers CD80, CD83, and HLA-DR, as well as cytokine/chemokine signatures, such as IL-1b, MIP-1a, and TNFa in primary human MoDC. We further validated our observations using the TruCulture® (Myriad RBM, Inc., Austin, TX, USA) whole-blood ex vivo culture system. Using this ex vivo system allowed us to measure immune-altering effects of commensal bacteria in primary human whole-blood. As such, we report that both these primary in vitro and ex vivo systems are robust and enable identification, stratification, and differentiation of various commensal bacteria as potential modulators of host immunity.
Highlights
Mounting evidence has shown that the host microbiome plays a critical role in proper development, maturation, and function of the host immune system
Primary human monocytes (CD14+) obtained from healthy human donors were differentiated into monocyte-derived dendritic cells (MoDC) and stimulated with 104 cfu or 104 particles of Fusobacterium nucleatum (Fn23726), Fusobacterium nucleatum (Fn25586), or Bacteroides fragilis (Bf43858) overnight (16–18 h) at 37 °C, 5% CO2, without agitation
Primary human monocytes (CD14+) obtained from healthy human donors were differentiated into MoDC and stimulated with 104 particles of heat-killed (HK) Bifidobacterium breve (Bb15700), Akkermansia muciniphila (AmBAA-835), Fusobacterium nucleatum (Fn23726), Bacteroides fragilis (Bf25285), Faecalibacterium prausnitzii (Fp27766), Enterococcus hirae (Eh8043), Bacteroides fragilis (Bf43858), or Fusobacterium nucleatum (Fn25586), or 1 μg/mL high molecular weight (HMW) polycytidylic acid (Poly I):C overnight (16–18 h) at 37 °C, 5% CO2, without agitation
Summary
Mounting evidence has shown that the host microbiome plays a critical role in proper development, maturation, and function of the host immune system This phenomenon has been well-characterized in germ-free murine studies, where the absence of a normal microbiome results in impaired host immune function [1,2] and in human clinical observational studies [3–5]. Current methods used to identify and rank potential immuno-modulators often fall short in characterizing the potential immune-altering properties of commensal bacteria. Much of this kind of work relies upon immortalized and/or non-primary cell lines for screening [13]. While in vivo animal models are often used as a complete biological system, there tends to be a lack of translatability from mouse to human Due to these pitfalls, it is likely that potential potent immuno-modulators have been either misidentified or missed entirely. Developing reliable and sensitive in vitro/ex vivo culture systems to identify and rank potential immuno-modulators of the host immune system is one of the first steps towards solving such a problem
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