Porcine reproductive and respiratory syndrome (PRRS), caused by the porcine reproductive and respiratory syndrome virus (PRRSV), is one of the major diseases threatening the swine industry. This study aims to rationally design and optimize natural antimicrobial peptides to identify antiviral candidates with potent inhibitory activity against PRRSV, thereby establishing a foundation for the development of novel preventive and therapeutic agents targeting PRRS. In this study, with cecropin D (CD) as the parent peptide, three derivatives (CD-2, CD-3, and CD-4) were designed through amino acid substitutions. CD and derived peptides were obtained by solid-phase peptide synthesis. MS and reversed-phase (RP)-HPLC were employed for sequence identification, purification, and purity analysis. The secondary structures of the peptides were investigated by circular dichroism spectroscopy. CellTiter 96^® AQueous one solution cell proliferation assay was used to evaluate the cytotoxicity of the peptides. The inhibitory activities and mechanisms of the peptides against PRRSV were studied by Western blotting, RT-qPCR, and indirect immunofluorescence assay. The MS and RP-HPLC results showed that CD and derived peptides were successfully synthesized, with the purity reaching up to 95%. Circular dichroism analysis revealed that the CD derivatives exhibited more stable and abundant α-helices in a cell membrane-mimicking environment. The MTS assay indicated that all tested peptides at 100 μg/mL had negligible cytotoxicity. The experimental results of the action phase of the peptide against PRRSV demonstrated that the derived peptides significantly enhanced antiviral activities at the viral entry stage compared with the parent peptide. This enhancement was attributed to the introduction of lysine, tryptophan, and phenylalanine, which increased the hydrophobicity and positive charge of the peptides. These findings provide a theoretical basis for the application and structural optimization of antiviral peptides and may offer a new strategy for preventing and controlling PRRSV.
Porcine respiratory and reproductive syndrome virus/physiology* ; Animals ; Swine ; Antiviral Agents/chemistry* ; Porcine Reproductive and Respiratory Syndrome/virology* ; Virus Internalization/drug effects* ; Antimicrobial Peptides/chemistry*

Lung squamous cell carcinoma with intratracheal diffuse leukoplakia as the main manifestation is very rare in clinic. The clinical data of a patient with pulmonary squamous cell carcinoma with intratracheal diffuse leukoplakia admitted to the Affiliated Hospital of Jining Medical University in December 25, 2021 were retrospectively analyzed in order to improve the understanding of this special manifestation. The patient was a 73-year-old male with clinical manifestations of cough, sputum, and blood-stained sputum. Chest CT indicated patchy high-density shadow on the upper right lung, whole-course thickening of trachea and bronchial walls, and bronchoscopy showed diffuse trachea-bronchial mucosa congestion and edema, with a large number of leukoplakia on the surface. The clinical effect was stable after 2 cycles of chemotherapy. Lung squamous cell carcinoma accompanied by diffuse leukoplakia in the trachea is a rare presentation. Chest CT can show thickening of the tracheal and bronchial wall, while the lesion and tumor signs of the primary lesion are not obvious. Electronic bronchoscopy as soon as possible can avoid missed diagnosis.