Next-generation sequencing and single-cell RT-PCR reveal a distinct variable gene usage of porcine antibody repertoire following PEDV vaccination

Host-pathogen interaction involving cytoskeleton changes as well as non-coding regulation as primary mechanisms for SRS resistance in Atlantic salmon

The salmonid rickettsial syndrome (SRS) is a systemic bacterial infection caused by Piscirickettsia salmonis that generates significant economic losses in Atlantic salmon (Salmo salar) aquaculture. Despite this disease's relevance, the mechanisms involved in resistance against P. salmonis infection are not entirely understood. Thus, we aimed at studying the pathways explaining SRS resistance using different approaches. First, we determined the heritability using pedigree data from a challenge test. Secondly, a genome-wide association analysis was performed following a complete transcriptomic profile of fish from genetically susceptible and resistant families within the challenge infection with P. salmonis. We found differentially expressed transcripts related to immune response, pathogen recognition, and several new pathways related to extracellular matrix remodelling and intracellular invasion. The resistant background showed a constrained inflammatory response, mediated by the Arp2/3 complex actin cytoskeleton remodelling polymerization pathway, probably leading to bacterial clearance. A series of biomarkers of SRS resistance, such as the beta-enolase (ENO-β), Tubulin G1 (TUBG1), Plasmin (PLG) and ARP2/3 Complex Subunit 4 (ARPC4) genes showed consistent overexpression in resistant individuals, showing promise as biomarkers for SRS resistance. All these results together with the differential expression of several long non-coding RNAs show the complexity of the host-pathogen interaction of S. salar and P. salmonis. These results provide valuable information on new models describing host-pathogen interaction and its role in SRS resistance.

FcRn Overexpression Expands Diversity of the Humoral Immune Response in bFcRn Transgenic Mice

The neonatal Fc receptor (FcRn) plays key roles in IgG and albumin homeostasis, maternal IgG transport, and antigen presentation of IgG-opsonized antigens. Previously, we reported that transgenic (Tg) mice that overexpress bovine FcRn (bFcRn) have augmented T-dependent humoral immune response with increased IgG protection, higher level of antigen-specific antibodies, greater number of antigen-specific B cells, and effective immune response even against weakly immunogenic epitopes. In this study we analyzed the diversity of the humoral immune response of bFcRn Tg mice, using a length distribution analysis (spectratyping) and next generation sequencing (NGS) of the immunoglobulin heavy chain variable regions. Our analysis showed that in response to immunization with ovalbumin or transfected cells that expressed a unique membrane protein, our Tg animals developed a more diverse plasma cell repertoire than controls, which manifested in greater numbers of different clones, and clusters with fewer highly expanded large clones, as identified by the variable region (CDR3) of the immunoglobulin heavy chain. The increased antibody diversity in Tg mice after immunization was observed at both IgM and IgG levels, indicating that the increased humoral immune diversity in Tg mice is due to a higher number of both activated, antigen-specific naïve and isotype switched B cells. We thus demonstrated that the BCR repertoire of the immunized bFcRn Tg animals is more diverse compared to wild type mice, which likely makes these Tg mice a better choice for monoclonal antibody production against challenging antigens, including the extracellular regions of cell membrane proteins.