The adjuvant BcfA activates antigen presenting cells through TLR4 and supports TFH and TH1 while attenuating TH2 gene programming

Front Immunol. 2024 Aug 29:15:1439418. doi: 10.3389/fimmu.2024.1439418. eCollection 2024.

Abstract

Introduction: Adjuvants added to subunit vaccines augment antigen-specific immune responses. One mechanism of adjuvant action is activation of pattern recognition receptors (PRRs) on innate immune cells. Bordetella colonization factor A (BcfA); an outer membrane protein with adjuvant function, activates TH1/TH17-polarized immune responses to protein antigens from Bordetella pertussis and SARS CoV-2. Unlike other adjuvants, BcfA does not elicit a TH2 response.

Methods: To understand the mechanism of BcfA-driven TH1/TH17 vs. TH2 activation, we screened PRRs to identify pathways activated by BcfA. We then tested the role of this receptor in the BcfA-mediated activation of bone marrow-derived dendritic cells (BMDCs) using mice with germline deletion of TLR4 to quantify upregulation of costimulatory molecule expression and cytokine production in vitro and in vivo. Activity was also tested on human PBMCs.

Results: PRR screening showed that BcfA activates antigen presenting cells through murine TLR4. BcfA-treated WT BMDCs upregulated expression of the costimulatory molecules CD40, CD80, and CD86 and produced IL-6, IL-12/23 p40, and TNF-α while TLR4 KO BMDCs were not activated. Furthermore, human PBMCs stimulated with BcfA produced IL-6. BcfA-stimulated murine BMDCs also exhibited increased uptake of the antigen DQ-OVA, supporting a role for BcfA in improving antigen presentation to T cells. BcfA further activated APCs in murine lungs. Using an in vitro TH cell polarization system, we found that BcfA-stimulated BMDC supernatant supported TFH and TH1 while suppressing TH2 gene programming.

Conclusions: Overall, these data provide mechanistic understanding of how this novel adjuvant activates immune responses.

Keywords: BcfA; T cell polarization; adjuvants; antigen presenting cells; pattern recognition receptors.

MeSH terms

  • Adjuvants, Immunologic* / pharmacology
  • Animals
  • Antigen-Presenting Cells / immunology
  • Antigen-Presenting Cells / metabolism
  • Cytokines / metabolism
  • Dendritic Cells / immunology
  • Humans
  • Lymphocyte Activation / immunology
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • T Follicular Helper Cells / immunology
  • Th1 Cells* / immunology
  • Th2 Cells* / immunology
  • Toll-Like Receptor 4* / immunology
  • Toll-Like Receptor 4* / metabolism

Substances

  • Toll-Like Receptor 4
  • Adjuvants, Immunologic
  • Tlr4 protein, mouse
  • Cytokines

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was supported by 1R01AI125560 and 1R01AI153829 (to PD and RD) and 1R01AI134972 (to KO). MS was supported by a doctoral fellowship from the Egyptian Bureau of Higher Education. KR was supported by The Ohio State University College of Medicine Advancing Research in Infection and Immunity Fellowship Program. JH is supported by NIAID 1T32AI165391-01. JT is supported by NIAID 1F30AI172189-01A1.