Evaluation of Ammonia Nitrogen Exposure in Immune Defenses Present on Spleen and Head-Kidney of Wuchang Bream (Megalobrama amblycephala).

Honghui Guo,Dapeng Li,Siqi Chen,Yingying Wang,Rong Tang,Hui Yang,Li Li,Kang Ouyang,Xi Zhang,Yu Kuang

doi:10.3390/ijms23063129

Abstract

Ammonia is one of the most important environmental factors in aquatic ecosystems. However, there are limited studies on the effects of chronic or long-term ammonia stress and its potential molecular mechanism in fish. This study aimed to investigate the immune response and molecular mechanisms in the spleen and head-kidney of fish following chronic ammonia exposure. Megalobrama amblycephala (9.98 ± 0.48 g) were exposed to different concentrations of total ammonia nitrogen (0–30 mg/L) for 30 days. Ammonia exposure caused significant increases in cortisol levels and decreases in lysozyme and complement 3/4 concentrations in the serum, indicating inhibitory effects of ammonia stress on innate immune responses. Ammonia exposure also induced concentration-dependent increases in ammonia concentrations in tissue, pathological damage and indexes of spleen and head-kidney. Additionally, the contents of immunoglobulin M (IgM), interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) as well as mRNA levels of toll-like receptors (TLRs)/Myeloid differentiation factor 88 (MyD88)-independent signaling molecules in the spleen and head-kidney were significantly downregulated after ammonia exposure. Our findings suggested that chronic ammonia exposure caused the suppression of innate and adaptive immune responses through downregulating TLR/MyD88-independent signaling. Adverse influences of chronic ammonia stress were more severe in the spleen than in the head-kidney.

Highlights

Ammonia is one of the most important environmental factors in aquatic ecosystems that affects the growth and health of aquatic animals [1]
Decreased mRNA levels of complement C3 and immunoglobulin M (IgM) were observed in the spleens of Pelteobagrus vachellii and Rhynchocypris lagowski under acute ammonia exposure [17,18]
Our present results showed that chronic ammonia exposure caused marked decreases in protein and transcriptional levels of splenic interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α), which were further supported by the Spearman correlation analysis between ammonia concentrations and the levels of splenic IL-1β and TNF-α

Summary

Introduction

Ammonia is one of the most important environmental factors in aquatic ecosystems that affects the growth and health of aquatic animals [1]. Ammonia nitrogen generally comes in one of two ionized forms—NH4+ and the un-ionized form, NH3, in the aquatic environment. High levels of ammonia frequently occur in aquatic environments due to disorderly discharges of sewage effluent, agricultural run-off, and high-density aquaculture [5–7]. In some studies on Takifugu rubripes, Scophthalmus maximus and Pelteobagrus fulvidraco, acute ammonia exposure could upregulate gene expression levels of B-cell activating factor, heat shock protein 70/90, tnf-α, and interleukin1/1β/6/8/12 [13–15]. Decreased mRNA levels of complement C3 and IgM were observed in the spleens of Pelteobagrus vachellii and Rhynchocypris lagowski under acute ammonia exposure [17,18]. Some investigators have reported adverse effects of ammonia nitrogen on mRNA expression of TLRs through transcriptional analysis [16,19–22]. We hypothesize that persistent ammonia exposure could affect fish immunity, in which the TLR signaling pathway might play an important role

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