A novel member of B-cell linker protein identified in lamprey, Lampetra japonica

Lamprey VLRB participates in pathogen detection, VLRB/L-BLNK/L-NF-κB (B-like cells) signal transduction, and development

In jawed vertebrates, B cell receptors (BCR) are primary pathogen detectors that activate downstream signaling pathways to express adaptive immune effectors. In jawless vertebrates, the variable lymphocyte receptors (VLR) B positive lymphocytes can express and secrete specific VLRB molecules in an analogous manner to that of immunoglobulins by B cells in jawed vertebrates. Our study is the first to demonstrate the possibility of incubation of fertilized eggs and artificial breeding of Lampetra morii larvae throughout their life cycle under laboratory condition. We also found that VLRB, lamprey B-cell linker (L-BLNK), and lamprey nuclear factor-kappa B (L-NF-κB) play key roles in early larval development. Aeromonas hydrophila was found to be a lethal pathogen of L. morii larvae causing rapid infection at a concentration of 10⁷ cfu/mL qRT-PCR results revealed that gene expression levels of VLRB, L-BLNK, and L-NF-κB were up-regulated significantly. Ten-day infection trials showed that VLRB, L-BLNK, and L-NF-κB are crucial for lamprey immune response. Furthermore, the expression levels of L-BLNK and L-NF-κB were down-regulated drastically both at mRNA and protein levels after bacterial infection than in the naive group of VLRB morphants. A similar expression pattern of VLRB and L-BLNK was found in L-NF-κB morphants post bacterial infection. The results were strikingly different in the other two morphants. The VLRB and L-NF-κB expression levels were found to be down-regulated at mRNA and protein levels by less than 30% and 45%, respectively, in L-BLNK morphants compared to those in the naive group. These results indicate that L-BLNK and L-NF-κB might participate in VLRB-mediated immune response. Additionally, in VLRB morphants, the mRNA expression levels of some genes, especially the ones expressed in VLRB⁺ lymphocytes but not in VLRA⁺ lymphocytes, were found to be affected. Therefore, these findings of B-like lymphocytes in lamprey offer key evidence with regard to the evolution of adaptive immunity.

Identification and functional analysis of grouper (Epinephelus coioides) B-cell linker protein BLNK

B-cell linker protein (BLNK) is an adaptor protein that plays a crucial role in the B cell antigen receptor (BCR) signal pathway. To investigate the function of BLNK in teleost fish, we cloned a BLNK ortholog gene from the orange-spotted grouper (Epinephelus coioides). Homology analysis showed that the grouper BLNK (EcBLNK) had a 34%-77% amino acid identity in comparison to other vertebrates and shared the highest amino acid identity with BLNK from the Asian seabass Lates calcarifer. EcBLNK comprises an N-terminal SAM domain and a C-terminal B-cell linker SH2 domain. Ten tyrosine residues were well conserved between teleost fish and mammals. Tissue distribution analysis showed that EcBLNK was expressed mainly in immune organs and expression was at the highest level in head kidney. Co-localization of EcBLNK and EcCD79a was observed in transfected HEK293T cells. Overexpression of EcBLNK did not activate nuclear factor kappa-light-chain-enhancer of activated B cells. The protein level of EcBLNK in grouper head kidney leukocytes was increased by stimulation with lipopolysaccharide. In groupers infected with Cryptocaryon irritans, EcBLNK was regulated in the infected sites and the systemic organ which suggests that EcBLNK was activated in the immune response to parasite infection.

A Novel Vav3 Homolog Identified in Lamprey, Lampetra japonica, with Roles in Lipopolysaccharide-Mediated Immune Response

Vav guanine nucleotide exchange factor 3 (Vav3), a Rho family GTPase, regulates multiple cell signaling pathways including those of T- and B-cell receptors in vertebrates through mediating the activities of the Rho family members. Whether the lamprey possesses Vav3 homolog and what role it plays in immune response remain unknown. Gene cloning, recombinant expression, antibody production and expression pattern analyses were performed to characterize the lamprey Vav3 in the current study. The lamprey Vav3 is closer to jawed vertebrates' Vav3 molecules (about 53% identities in general) than to Vav2 molecules of jawless and jawed vertebrates (about 51% identities in general) in sequence similarity. Conserved motif analysis showed that the most distinguished parts between Vav3 and Vav2 proteins are their two Src-homology 3 domains. The relative expression levels of lamprey vav3 mRNA and protein were significantly up-regulated in lamprey lymphocytes and supraneural myeloid bodies after mixed-antigens stimulation, respectively. In addition, lamprey Vav3 were up-regulated drastically in lymphocytes and supraneural myeloid bodies after lipopolysaccharide (LPS) rather than phytohemagglutinin (PHA) stimulation. Lamprey Vav3 distributed in the cytoplasm of variable lymphocyte receptor B positive (VLRB⁺) lymphocytes, and the number of plasmacytes (VLRB and lamprey Vav3 double positive) in blood lymphocytes also increased after LPS stimulation. Our results proved that lamprey Vav3 was involved in the LPS-mediated immune reaction of lamprey and provided a clue for the further study of the precise role lamprey Vav3 played in the signaling pathway of lamprey VLRB⁺ lymphocytes.

Identification and characterisation of the immune response properties of Lampetra japonica BLNK

B cell linker protein (BLNK) is a central linker protein involved in B cell signal transduction in jawed vertebrates. In a previous study, we have reported the identification of a BLNK homolog named Lj-BLNK in lampreys. In this study, a 336 bp cDNA fragment encoding the Lj-BLNK Src homology 2 (SH2) domain was cloned into the vector pET-28a(+) and overexpressed in Escherichia coli BL21. The recombinant fragment of Lj-BLNK (rLj-BLNK) was purifiedby His-Bind affinity chromatography, and polyclonal antibodies against rLj-BLNK were raised in male New Zealand rabbits. Fluorescenceactivated cell sorting (FACS) analysisrevealed that Lj-BLNK was expressed in approximately 48% of the lymphocyte-like cells of control lampreys, and a significant increase in Lj-BLNK expression was observed in lampreys stimulated with lipopolysaccharide (LPS). Western blotting analysis showed that variable lymphocyte receptor B (VLRB) and Lj-BLNKwere distributed in the same immune-relevant tissues, and the levels of both were upregulated in supraneural myeloid bodies and lymphocyte-like cells after LPS stimulation. Immunofluorescence demonstrated that Lj-BLNK was localized in VLRB(+) lymphocyte-like cells. These results indicate that the Lj-BLNK protein identified in lampreys might play an important role in the VLRB-mediated adaptive immune response.