Crustins are crustacean cationic cysteine-rich antimicrobial peptides that contain one or two whey acidic protein (WAP) domain(s) at the carboxyl terminus and mainly show antimicrobial and/or proteinase inhibitory activities. Here, we performed genome and transcriptome screening and identified 34 full-length crustin-like encoding genes in Litopenaeus vannamei. Multiple sequence analysis of the deduced mature peptides revealed that these putative crustins included 10 type Ia, two type Ib, one type Ic, 11 type IIa, three type IIb, four type III, one type IV, one type VI, and one type VII. These putative crustins were clustered into different groups. Phylogenetic analysis, considering their domain composition, showed that different types of crustin-like genes in crustaceans might be originated from the WAP core region, along with sequence insertion, duplication, deletion, and amino acid substitution. Tissue distribution analysis suggested that most crustin-like genes were mainly detected in immune-related tissues while several crustin-like genes exhibited tissue-specific expression patterns. Quantitative PCR analysis on 15 selected crustin-like genes showed that most of them were apparently upregulated after Vibrio parahaemolyticus or white spot syndrome virus (WSSV) infection. One type Ib crustin-like gene, mainly expressed in the ovary, showed the highest expression levels before the gastrula stage and was hardly detected after the limb bud stage, suggesting that it was a maternal immune effector. Collectively, the present data revealed the molecular and functional diversity of crustins and their potential evolutionary routes in crustaceans.

As a kind of antimicrobial peptides (AMP) in crustacean, anti-lipopolysaccharide factors (ALFs) have broad spectrum antimicrobial activities. In the present study, we identified four ALF genes, EcALF2-5, from the ridgetail prawn Exopalaemon carinicauda. Tissue distribution analysis showed that EcALF2 and EcALF4 transcripts were mainly located in gill, epidermis, and stomach, while EcALF3 and EcALF5 were mainly in hemocytes. Peptides corresponding to the LPS binding domain (LBD) of EcALFs were synthesized for analyzing their antimicrobial activities. Minimal inhibitory concentration (MIC) analysis showed that the synthetic LBD peptides of EcALF3 and EcALF4 could inhibit the growth of Gram-positive and Gram-negative bacteria, while the synthetic LBD peptides of EcALF2 and EcALF5 showed antibacterial activity against Vibrio. Incubation of white spot syndrome virus (WSSV) with the synthetic LBD peptides of EcALF3, EcALF4, and EcALF5 could reduce the in vivo viral copy number in WSSV-infected prawns. After silencing of EcALFs, Vibrio exhibited a rapid proliferation in the hepatopancreas of the prawn. The present data showed the important function of different EcALFs in modulating the in vivo bacterial and viral propagation in E. carinicauda. This study will provide new clues into the disease control in aquaculture.

Invertebrates rely exclusively on innate immunity but exhibit memory-like responses termed immune priming or trained immunity. In the commercially vital whiteleg shrimp (Litopenaeus vannamei), infection by Vibrio parahaemolyticus causes severe economic losses, yet the molecular networks driving secondary immune recall remain poorly understood. In this study, we established a two-step immune challenge model in L. vannamei using formaldehyde-inactivated V. parahaemolyticus and performed transcriptomic analysis on hemocytes to compare primary and secondary immune responses. Differentially expressed gene (DEG) screening and enrichment analyses (GO, KEGG, and GSEA) suggest that shrimp hemocytes undergo a broad and coordinated transcriptional reprogramming rather than uniform upregulation of immune genes. Transcriptomic data show potential associations between secondary immune priming and the modulation of cell fate processes: genes related to cell cycle progression (e.g., CDK1, CCNB3) and spindle assembly (e.g., MPS1) were significantly upregulated alongside apoptosis inhibition (CASP6 downregulation). Concurrently, metabolic remodeling was observed through the upregulation of lipid synthesis (SREBF1, FASN) and carbohydrate uptake pathways, potentially providing anabolic support for hemocyte growth and immune activation. Furthermore, the humoral effector responses appear to be strengthened, characterized by upregulated antimicrobial peptides (PEN, ALF) and the proPO melanization cascade (PPAF3, PPO3), whereas the expression of intracellular NLR was relatively suppressed, which might help mitigate excessive immune inflammation and immunopathological damage. Collectively, these transcriptomic findings identify a putative coordinated transcriptional signature of hemocyte recall responses in L. vannamei. This study expands our understanding of innate immune memory in invertebrates and provides candidate molecular markers for further study in disease-resistant breeding research in shrimp aquaculture.