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

Abstract

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 Ichthyophthirius multifiliis (Ich) infection and may serve as predictors of disease outcome. To elucidate their spatiotemporal dynamics, the full-length CDS of IL-1β, IL-6, and SAA in Pelteobagrus vachelli 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 IL-1β expression in the kidney and SAA expression in the spleen at 5 days post-infection (dpi), coinciding with no visible symptoms. Significant SAA 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 SAA downregulation at 20 dpi, when 40% of fish presented with white spots. Complete clinical resolution by 40 dpi correlated with reduced hepatic SAA and branchial IL-1β 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.

Keywords: Ichthyophthirius multifiliis; Pelteobagrus vachelli; interleukin-1β; interleukin-6; serum amyloid A.

Figure 1

PCR amplification products of SAA, IL-6, and IL-1β of darkbarbel catfish. Lane M, DNA marker; lane 2, lane 3, and lane 5, negative control; lane 1, positive amplification of SAA; lane 4, positive amplification of IL-6; lane 6, positive amplification of IL-1β.

Figure 2

Phylogenetic trees of SAA, IL-1β, and IL-6. Red font represent the present GenBank ID of present study.

Figure 3

Clinical and histopathological symptoms of dying darkbarbel catfish. (A). Schedule of sampling. (B). Morbidity of fish post-infection. (C). Moribund fish infected by Ich. (D). Microscopic observation of gills, wet mount. (E). Histopathological observation of gills. Red box Trophonts, HE staining.

Figure 4

Heat map showing the relative gene expression in seven tissues at different time points. Infected fish compared to control fish. *: significant differences from control fish, 0.01 < p < 0.05. **: Obvious significant differences from control fish, p < 0.01. The hierarchical clustering orders the rows based on similarity.

Figure 5

The expression of SAA, IL-6, and IL-1β genes after infection with Ich at various time points (0, 5, 10, 20, and 40 dpi and moribund fish). Bars and error lines represent geometrical means and geometrical standard deviations. The expression levels between infected time points and uninfected time points are significantly different (0.01 < p < 0.05), where the symbol * over the bars represents significant differences and ** over the bars represents extremely significant differences (p < 0.01).