Spatiotemporal Dynamics of Pro-Inflammatory Mediator Expression in Pelteobagrus vachelli During Ichthyophthiriasis: A 40-Day Longitudinal Study of IL-1β, IL-6, and SAA

Interleukin-1β (IL-1β), interleukin-6 (IL-6), and serum amyloid A (SAA) are key pro-inflammatory mediators in the regulation of immune responses. The hypothesis posits that their expression varies with the progression of <i>Ichthyophthirius multifiliis</i> (Ich) infection and may serve as predictors of disease outcome. To elucidate their spatiotemporal dynamics, the full-length CDS of <i>IL-1β</i>, <i>IL-6</i>, and <i>SAA</i> in <i>Pelteobagrus vachelli</i> were cloned, and then their mRNA levels were tracked from infection onset (day 0) to resolution (day 40) or mortality in seven tissues. Key findings revealed a surge in <i>IL-1β</i> expression in the kidney and <i>SAA</i> expression in the spleen at 5 days post-infection (dpi), coinciding with no visible symptoms. Significant <i>SAA</i> elevation in the head kidney was observed at 10 dpi, preceding the emergence of white spots on the skin. This was followed by gill-specific <i>SAA</i> downregulation at 20 dpi, when 40% of fish presented with white spots. Complete clinical resolution by 40 dpi correlated with reduced hepatic <i>SAA</i> and branchial <i>IL-1β</i> levels. Notably, the concurrent upregulation of all three mediators occurred exclusively in the skin of moribund individuals. These findings identify potential biomarkers for tracking host inflammatory responses in ichthyophthiriasis.