The bovine IgG1 Fc receptor (boFcγRIII) is a homologue to human FcγRIII (CD16) that binds bovine IgGI with medium–low affinity. In order to identify the Fc-binding site on the bovine IgG1 Fc receptor (boFcγRIII), peptides derived from the second extracellular domain (EC2) of boFcγRIII were synthesized and conjugated with the carrier protein. With a Dot-blot assay, the ability of the peptides to bind bovine IgG1 was determined, and the IgG1-binding peptide was also identified via truncation and mutation. The minimal peptide AQRVVN corresponding to the sequence 98–103 of boFcγRIII bound bovine IgG1 in Dot-blot, suggesting that it represents a linear ligand-binding site located in the putative A–B loop of the boFcγRIII EC2 domain. Mutation analysis of the peptide showed that the residues of Ala⁹⁸, Gln⁹⁹, Val¹⁰¹, Val¹⁰² and Asn¹⁰³ within the Fc-binding site are critical for IgG1 binding on boFcγRIII. The functional peptide identified in this paper is of great value to the IgG–Fc interaction study and FcR-targeting drug development.

The emergence of highly pathogenic avian influenza viruses (AIVs) poses significant threats to global public health and the poultry economy. Rapid detection methods targeting the hemagglutinin (HA) protein have become increasingly unreliable due to ongoing antigenic drift and genetic mutations. In this study, we screened two monoclonal antibodies (mAbs) against the highly conserved neuraminidase (NA) protein, which were characterized by high affinity and specificity for the N9 subtype. Using the paired mAbs 12A2 and 12F12, an NA-targeting lateral flow immunoassay (NA-LFIA) was developed for the rapid detection of N9 subtype AIVs. The NA-LFIA demonstrated exceptional specificity, exhibiting no cross-reactivity with the N1, N2, or N6 subtypes. The limits of detection (LODs) were established at 10^3.3 TCID₅₀/0.1 mL for the virus and 98 ng/mL for the recombinant NA protein. The test strips exhibited excellent reproductivity for detecting the NA antigen, with intra-assay and inter-assay variations of 5.32% and 6.05%, respectively. Stability testing confirmed a six-month shelf life without any loss of sensitivity. These finds indicate that the NA-LFIA is a robust, rapid point-of-care testing (POCT) tool for the early detection of N9 subtype AIV infection.

Duck viral hepatitis is very common in China, causing significant impact and economic losses to the duck farming industry. Currently, DHAV-3 has become the main factor causing duck viral hepatitis in China. However, the existing DHAV-3 vaccines cannot completely rule out the potential risk of the vaccine strain becoming more virulent. Due to the high similarity in genomic sequences between wild strains and vaccine strains (with only a few base differences), traditional detection methods struggle to accurately differentiate them, severely interfering with disease control decisions. Therefore, simultaneously detecting both the virulent strain and the attenuated strain of DHAV-3 is crucial for evaluating vaccine efficacy, monitoring virus mutations, and optimizing control strategies. This study, using the DHAV-3 SD70 attenuated strain as an example, developed a highly sensitive and rapid detection method to identify and distinguish between the DHAV-3 virulent and SD70 attenuated strains, providing a new strategy for identifying both strains. Currently, there are no literature reports on the detection methods for the two strains. Therefore, we propose a single-base recognition system strategy based on RPA-CRISPR. DHAV-3 virulent and attenuated strains were specifically identified by this method based on only a few different base sequences. This method can detect two target genes as low as 10° copy/μL within 35 min. In addition, when this method was used for samples analysis, the results of this method, sequencing results, and the results provided by the company were compared and found to be consistent. This method has the advantages of fast speed, simple operation, high specificity and sensitivity, which can be used for the detection of DHAV-3 virulence strain and SD70 attenuated strain, and lays a technical foundation for disease control, vaccine evaluation and mutation monitoring.