Immunological characterization of probiotic (Saccharomyces cerevisiae) on splenic histomorphology in broiler chickens

Objective To evaluate the effects of Saccharomyces cerevisiae ( SC ) on splenic activity in broiler chickens. Chickens were randomly assigned to two groups: a control group (CG) without SC supplementation and the cerevisiae-supplemented group (PG). Morphometric and stereological analyses were performed to assess germinal centers (GC). Spleens from 16 Ross broiler chickens were analyzed using the Romppanen’s equations (1981). For each sample, five microscopic fields were evaluated to quantify GC number, area, density, diameter, distance to the nearest neighbor in the section plane (Δ2), and spatial distance to the nearest neighbor (Δ3). Statistical comparisons were performed using unpaired t-tests (parametric) or Mann–Whitney tests (nonparametric) with P < 0.05 considered statistically significant. Immunohistochemistry (IHC) was used to characterize and quantify immune cell populations including T cells (CD3+, CD4+, CD8+, Tregs [CD25+]), macrophages (CD163+), and B cells (CD20+) per mm 2 . SC supplementation exhibited significantly lower GC count per mm 2 compared to the control group. PG showed higher spatial distance to the nearest neighbor (Δ3) than CG. IHC analysis revealed a lower density and percentage of CD3 T cells in PG compared to CG. The findings suggest that SC exerts immunomodulatory effects, likely mediated by interactions between its cell wall components (e.g., SOM and β-glucans) and TLR2/TLR4 receptors on dendritic cells and macrophages in the gastrointestinal tract. This interaction may attenuate excessive inflammatory responses, indirectly reducing splenic GC formation and CD3+ lymphocyte density.