Peanut protein acts as a Th2 adjuvant by inducing expression of RALDH2 in human antigen-presenting cells in a TLR2-dependent manner

Authors: RUITER, BERT - Massachusetts General Hospital; SMITH, NEAL - Massachusetts General Hospital; FLEMMING, ELIZABETH - Massachusetts General Hospital; PATIL, SARITA - Massachusetts General Hospital; Hurlburt, Barry; Maleki, Soheila; SHREFFLER, WAYNE - Massachusetts General Hospital

Submitted to: Journal of Allergy Clinical Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2020
Publication Date: 7/1/2021
Citation: Ruiter, B., Smith, N.P., Flemming, E., Patil, S.U., Hurlburt, B.K., Maleki, S.J., Shreffler, W.G. 2021. Peanut protein acts as a Th2 adjuvant by inducing expression of RALDH2 in human antigen-presenting cells in a TLR2-dependent manner. Journal of Allergy Clinical Immunology. 148(1):182-194. https://doi.org/10.1016/j.jaci.2020.11.047.
DOI: https://doi.org/10.1016/j.jaci.2020.11.047

Interpretive Summary: Peanut allergy is a response to the host immune system interacting with peanut proteins. One important aspect is the activation of antigen presenting cells. This manuscript describes work done to reveal the mechanisms behind activation.

Technical Abstract: Background: Peanut is a potent inducer of pro-allergenic Th2 responses in susceptible individuals. Antigen-presenting cells (APC) instruct naïve T cells to differentiate into various effector cells determining immune responses such as allergy or tolerance. Objective: We sought to detect peanut protein (PN)-induced changes in gene expression in human myeloid dendritic cells (mDC) and monocytes, identify signaling receptors, and assess the role of PN-induced transcriptional changes in mDC in their subsequent ability to promote T cell differentiation. Methods: mDC, monocytes, and naïve CD4+ T cells were isolated from blood bank donors and peanut-allergic patients. APC were incubated with PN and various other stimulants, and mRNA was isolated for microarray and RT-qPCR. To assess T cell differentiation, mDC were co-cultured with naïve Th cells. Results: PN induced a unique gene expression profile in mDC, including the gene that encodes RALDH2, a rate-limiting retinoic acid (RA)-producing enzyme. Stimulation of mDC with PN also induced a 7-fold increase in enzymatic activity of RALDH2. Blocking antibodies against TLR1/TLR2, as well as siRNA targeting TLR1/TLR2, reduced expression of RALDH2 in PN-stimulated APC by 70%. Naïve Th cells co-cultured with PN-activated mDC showed an RA-dependent 4-fold increase in production of IL-5 and expression of integrin a4ß7. Conclusions: PN induces RALDH2 in human APC by signaling through the TLR1/TLR2 heterodimer. This leads to production of RA, which acts on Th cells to induce IL-5 and gut-homing integrin. RALDH2 induction by PN in APC and RA-promoted Th2 differentiation could be an important factor determining allergic responses to peanut.