Staphylococcal enterotoxins (SE) crosslink the MHC-II on antigen-presenting cells (APC) with the T-cell receptor, inducing a polyclonal T-cell response. Although APCs are the initial targets of SE and are critical in shaping subsequent T-cell activation, the effects of SE on APC function remain poorly understood. This study investigates the immunomodulatory effects of staphylococcal enterotoxin A (SEA) on monocytes and their differentiation into monocyte-derived dendritic cells (moDC) or macrophages (MDM). Transcriptomic analyses of human monocytes via RNA sequencing revealed SEA-induced enrichment of gene pathways associated with inflammation, infection and dermatitis, with these effects amplified in the presence of T-cells. Phenotypic and functional characterization showed that SEA-primed monocytes differentiated into MDM with an altered polarization, deviating from classical M1/M2 pathways. SEA-primed MDM exhibited downregulayion of key markers including HLA-DR, CD80. CD86 and PD-L1. Functional assays demonstrated that SEA-primed MDM drived hyperinflammatory T-cell responses, with significantly enhanced proliferation and IFN-γ secretion. In contrast. moDC retained robust antigen-presenting capabilities even upon SEA-priming. These findings provide mechanistic insights into SEA-mediated immune modulation, illustrating how SEA reprograms MDM functions and amplify proinflammatory T-cell responses. This advances our understanding of superantigen-driven immune interactions, offering a foundation for developing therapeutic strategies to mitigate superantigen-mediated immune conditions.

Staphylococcal enterotoxins (SE) pose a great threat to human health due to their ability to bypass antigen presentation and activate large amounts of conventional T cells resulting in a cytokine storm potentially leading to toxic shock syndrome. Unconventional T- and NK cells are also activated by SE but the mechanisms remain poorly understood. In this study, the authors aimed to explore the underlying mechanism behind SE-mediated activation of MAIT-, γδ T-, and NK cells in vitro. CBMC or PBMC were stimulated with the toxins SEA, SEH, and TSST-1, and cytokine and cytotoxic responses were analyzed with ELISA and flow cytometry. All toxins induced a broad range of cytokines, perforin and granzyme B, although SEH was not as potent as SEA and TSST-1. SE-induced IFN-γ expression in MAIT-, γδ T-, and NK cells was clearly reduced by neutralization of IL-12, while cytotoxic compounds were not affected at all. Kinetic assays showed that unconventional T cell and NK cell-responses are secondary to the response in conventional T cells. Furthermore, co-cultures of isolated cell populations revealed that the ability of SEA to activate γδ T- and NK cells was fully dependent on the presence of both monocytes and αβ T cells. Lastly, it was found that SE provoked a reduced and delayed cytokine response in infants, particularly within the unconventional T and NK cell populations. This study provides novel insights regarding the activation of unconventional T- and NK cells by SE, which contribute to understanding the vulnerability of young children towards Staphylococcus aureus infections.

To the Editor,

Staphylococcus (S.) aureus is an intermittent or permanent skin colonizer in 90% of patients with airway diseases, and staphylococcal enterotoxin-IgE serum levels have been linked to both allergy and severe asthma.1, 2 During pregnancy, immune adaptation is required to ensure fetal growth,3 and type 2 responses are enhanced. These changes potentially worsen allergic conditions and increase the susceptibility to certain infections.4

Here we investigate the immune response to Staphylococcal enterotoxin A (SEA), a strong inducer of type 1 responses, in individuals with Th2-skewing,5 using peripheral blood mononuclear cells (PBMC) from allergic and non-allergic, pregnant and non-pregnant women6 (Figure 1A). Staphylococcal enterotoxins cause polyclonal T cell activation crosslinking the MHC-II on antigen-presenting cells (APCs) to the T-cell receptor (TCR) on T-cells (Figure 1B), leading to a strong proinflammatory response, potentially increasing IgE-production or disrupting the maternal-fetal tolerance.