Modulation of BCG-induced immune response using β-glucan: boosting immune regulation and reducing severe inflammatory reactions

BCG (Bacillus Calmette-Gue´rin) vaccination is well-known for its ability to stimulate immune responses, which lead to trained immunity and various inflammatory responses. The addition of β-glucan, a recognized immunomodulator, may help redirect this response toward a more balanced immune response. The interaction between BCG and β-glucan in modulating monocyte and macrophage populations remains an unexplored topic. Aim of this study was to investigate the effects of BCG and β-glucan on immune cell populations in mice. Sixteen animals were divided into four test groups, with three groups receiving intraperitoneal treatment with BCG, β-glucan, or a combination of both. Flow cytometry analysis of peritoneal cells, spleen, bone marrow, and PBMC showed varying immune responses among the groups. BCG alone triggered a robust inflammatory reaction, increasing the population of M1 macrophages and dendritic cells, along with the expression of MHCII and CD11b. β-glucan also expanded these populations, indicating independent immune activation. However, in the BCG+β-glucan group, a decrease in inflammatory monocytes was observed, suggesting that β-glucan tempers excessive inflammation when combined with BCG. The reduction of MHCII+CD11blowF4/80+CD11c- macrophages in BCG+β-glucan group compared to the β-glucan group alone suggests that β-glucan modulates BCG-induced inflammation by favoring immune regulation over prolonged activation. Furthermore, MHCII+CD19+ B cells were progressively reduced in the BCG and β-glucan group, most significantly in the BCG+β-glucan group, indicating a shift in B cell dynamics toward regulatory or antibody-secreting phenotypes. These findings indicate that β-glucan does not merely enhance BCGinduced activation but modulates it, balancing inflammatory and regulatory immune pathways. The combination of BCG and βglucan leads to controlled immune activation, limiting excessive inflammation while supporting immune adaptation. *The authors marked with an asterisk equally contributed to the work.