LECT2 Protects Nile Tilapia (Oreochromis niloticus) Against Streptococcus agalatiae Infection

Abstract

Leukocyte cell-derived chemotaxin 2 (LECT2) is a multifunctional cytokine that especially plays an important role in innate immune. However, the roles of LECT2 in the immune response of the economically important fish Nile tilapia (Oreochromis niloticus) against bacterial infection remains unclear. In this study, a lect2 gene from Nile tilapia (On-lect2) was identified, and its roles in the fish’s immune response against bacterial infection were determined and characterised. On-lect2 contains an open reading frame of 456 bp that encodes a peptide of 151 amino acids, as well as the conservative peptidase M23 domain. On-LECT2 is 62%–84% identical to other fish species and about 50% identical to mammals. The highest transcriptional level of On-lect2 was detected in the liver, whereas the lowest levels were detected in the other tissues. Moreover, the On-LECT2 protein is located mainly in the brain and head kidney. The transcriptional levels of On-lect2 substantially increased in the head kidney, brain, liver and spleen after Streptococcus agalactiae infection. Knockdown On-lect2 led to higher mortality due to liver necrosis or haemorrhage and splenomegaly. In vitro analysis indicated that the recombinant protein of On-LECT2 improved phagocytic activity of head kidney-derived macrophages. In vivo challenge experiments revealed several functions of On-LECT2 in the immune response of Nile tilapia against bacterial infection, including promotion of inflammation, reduction of tissue damages and improvement of survival rate.

Serotonin system is partially involved in immunomodulation of Nile tilapia (Oreochromis niloticus) immune cells

“…Specifically, their expression levels were mainly suppressed in the brain while mainly promoted in rest organs including head kidney, intestine, liver, and spleen. Based on our previous research ( 37 ) and Yi’s ( 24 ) & Cao’ s studies ( 27 ), various Nile tilapia organs rapidly respond to S. agalactiae infection. The peritoneal injection usually leads to a first response occurring in the peripheral immune organs such as the head kidney and spleen and a hysteretic response in the brain.…”

Vasoactive Intestinal Peptide (VIP) Protects Nile Tilapia (Oreochromis niloticus) against Streptococcus agalatiae Infection

“…However, the expression levels of On-VIP were remarkably increased in the brain at 24 h after infection. Therefore, the VIP in the head kidney and intestine was upregulated faster than that in the brain, which was because the stress reaction induced by intraperitoneal injection was usually rapid in peripheral immune organs, such as the intestine, and sluggish in the brain [ 34 , 35 ]. Briefly, results implied that On-VIP was probably implicated in Nile tilapia’s immunological response to S. agalactiae , as well as showing that fish still have functional neuro-immune communication.…”

CRP Involved in Nile Tilapia (Oreochromis niloticus) against Bacterial Infection

“…Subsequently, 100 fish were randomly collected and divided into two groups, namely, the S. agalactiae group and A. hydrophila group, with 50 fish per group. Then, all fish in each group were intraperitoneally injected with S. agalactiae (5 × 10 7 CFU/mL, 100 µL per fish) [ 24 ] or A. hydrophila (5 × 10 7 CFU/mL, 100 µL per fish), respectively. For each group, three fish were sacrificed at five different time points (0 h, 6 h, 12 h, 24 h, and 48 h) post challenge and five tissues including the brain, head kidney, intestine, liver, and spleen, were collected and RNA extracted and cDNA synthesized immediately from them.…”

“…Nile tilapia HKLs were prepared as previously described [ 24 ]. Briefly, three healthy fish were sacrificed as mentioned above and then the head kidney of each fish was separated, cut, and sieved through a 40 μm stainless nylon mesh (Greiner Bio-OneGmbH, Frickenhausen, Germany) for collecting the cells which were suspended in Leibovitz’s L-15 Medium (Thermo Fisher Scientific, Waltham, USA).…”

“…Daily statistical mortality, as well as the survival rate (SR) from the challenge test for seven days, were calculated following our previous iterative calculation formula [ 24 ]. …”