Toll-like Receptor Type 2 and 13 Gene Expression and Immune Cell Profiles in Diploid and Triploid Sterlets (Acipenser ruthenus): Insights into Immune Competence in Polyploid Fish

Toll-like receptors (TLRs) are key components of the innate immune system in fish, responsible for recognizing pathogen-associated molecular patterns derived from bacteria, viruses, and fungi. The sterlet (<i>Acipenser ruthenus</i>), an endangered sturgeon species valued for its meat and caviar, is a promising model for studying the effects of polyploidy on immune gene regulation. This study examined the expression of Toll-like receptor type 2 (<i>TLR2</i>) and type 13 (<i>TLR13</i>) in the heart, liver, gills, spleen, and kidney of diploid and triploid healthy sterlets using real-time PCR. <i>TLR2</i> and <i>TLR13</i> were expressed in all tissues of both diploids and triploids. In diploids, <i>TLR2</i> expression was the highest in the kidney and the lowest in the liver (<i>p</i> < 0.05). Similarly, <i>TLR13</i> expression in diploids was highest in the kidney and gills, and lowest in the liver (<i>p</i> < 0.05). In triploids, no significant tissue-specific variation in <i>TLR</i> expression was observed (<i>p</i> > 0.05). Comparisons between diploid and triploid sterlets revealed higher <i>TLR2</i> expression in the kidney and higher <i>TLR13</i> expression in the heart and kidney of diploids (<i>p</i> < 0.05). These molecular findings were supported by leukocyte analysis, which showed a significantly lower percentage of lymphocytes and a higher proportion of neutrophils in triploids compared to diploids. Additionally, the proportion of thrombocytes was significantly elevated in triploids (<i>p</i> < 0.05). This study provides the first report of <i>TLR</i> expression in polyploid fish, offering new insights into immune modulation associated with polyploidy in sturgeons.