Immunostimulatory activity of Pichia kluyveri, Hanseniaspora uvarum, Candida intermedia, Saccharomyces boulardii and their derivatives on RAW 264.7 macrophages

Non-Saccharomyces yeasts emerge as possible new probiotics with a beneficial effect equal to or greater than the reference probiotic yeast, Saccharomyces boulardii. In this work, we evaluated the immunomodulation effect caused by Candida intermedia in mice vaccinated with inactivated SARS-CoV-2. We conducted preliminary tests using murine macrophages (RAW 264.7) stimulated with viable and heat-killed yeast cells, culture supernatant, and DNA, using qPCR to detect the mRNA transcription. Next, mice were supplemented with C. intermedia before each dose of the SARS-CoV-2 vaccine, and then antibody production was measured by ELISA. The probiotic strain S. boulardii CNCM I-745 was used as a control. We also explored the differences in fecal microbiomes between the non-supplemented and supplemented groups. Live cells of C. intermedia increased the transcription of IL-4, IL-13, and STAT3 by macrophages RAW 264.7, while heat-killed cells up-regulated TNF and Bcl6, and the culture supernatant positively impacted TLR2 transcription. Concanavalin, zymosan, and lipopolysaccharide were used to stimulate splenocytes from C. intermedia-supplemented animals, which showed increased transcription of TNF, IFN{gamma}, IL-4, Bcl6, and STAT3. Sera from these animals showed enhanced levels of anti-SARS-CoV-2 IgG, as well as IgG1 and IgM isotypes, and sIgA in fecal samples. The microbiome of the C. intermedia-supplemented group showed a higher abundance of Bacteroides spp. and Clostridium spp., impacting the Bacteroidetes/Firmicutes balance. We concluded that C. intermedia and S. boulardii could stimulate and impact the gene expression of cells important for innate immunity, influence the composition of the gastrointestinal microbiome, and primarily boost the humoral response after vaccination. Statements and Declarations FundingThe present work was carried out with the support of Conselho Nacional de Desenvolvimento Cientifico (CNPq, Brazil), grant number 150538/2021-9.