Molecular Characterization of a B Cell Adaptor for Phosphoinositide 3-Kinase Homolog in Lamprey (Lampetra japonica) and Its Function in the Immune Response

Abstract

Human B cell adaptor for phosphoinositide 3-kinase (BCAP) is identified as an adaptor protein expressed in B cells and plays a critical immunomodulatory role in B cell receptor signaling and humoral immune response. In the current study, a homolog of BCAP (Lja-BCAP) was identified in Lampetra japonica. The open reading frame of Lja-BCAP contains 2181bp nucleotides and encodes a protein of 726 amino acids. After being stimulated by mixed bacteria, the mRNA and protein expression levels of Lja-BCAP and the activation levels of tyrosine kinases increased significantly in peripheral blood lymphocytes, gills and supraneural myeloid bodies, respectively. However, after the knockdown of Lja-BCAP by RNAi in vivo, the activation of tyrosine kinases was inhibited in the above tissues, which indicated that Lja-BCAP participated in the anti-bacterial immune response of lampreys. After lipopolysaccharide (LPS) stimulation, the expression of Lja-BCAP in peripheral blood lymphocytes, gills and supraneural myeloid bodies were significantly up-regulated 2.5, 2.2, and 11.1 times (p < 0.05) compared to the control group, respectively; while after phytohemagglutinin (PHA) stimulation, the up-regulation of Lja-BCAP was only detected in peripheral blood lymphocytes. The above results show that Lja-BCAP mainly participates in the LPS-mediated immune response of lampreys.

Updating Our Knowledge on Fish Immunology

“…Included in this Special Issue, these studies dealt with highly relevant fish species for the aquaculture sector and local human supply in Asiatic countries as well as worldwide, as in the case of tilapia. Therefore, the following studies focused on the inflammasome component apoptosis-associated speck-like protein containing a CARD domain (ASC) in the large yellow croaker ( Larimichthys crocea ) [ 3 ]; the B-cell adaptor for phosphoinositide 3-kinase (BCAP) homolog in the lamprey ( Lampetra japonica ) [ 4 ]; the CD68 gene from the Wuchang bream ( Megalobrama amblycephala ) (Cui et al); the complement factor I (CFI) gene in the grass carp ( Ctenopharyngodon Idella ) [ 5 ]; and the complement C3 protein [ 6 ], the serum amyloid P component (SAP) [ 7 ], the vasoactive intestinal peptide (VIP) and its receptor (VIPR1) [ 8 ], and the tartrate-resistant acid phosphatase type 5b (TRAP5b) [ 9 ] genes in the Nile tilapia ( Oreochromis niloticus ). Interestingly, Nile tilapia specimens with over or knockdown expression of TRAP5b showed significantly lower or higher bacterial loads, respectively, upon in vivo infection with Streptococcus agalactiae [ 9 ].…”

“…It is very interesting to note how CD68 antiserum was generated to help identify CD68+ve cells and how they increased upon bacterial challenge and by LPS incubation, suggesting that it could be considered a good marker for macrophages [ 10 ]. In addition, lamprey BCAP protein levels, and its tyrosine kinase activity, were increased in peripheral blood lymphocytes, gills, and supraneural myeloid bodies upon bacterial infection as well as via lipopolysaccharide (LPS) stimulation, but not phytohemagglutinin (PHA), thus pointing to a role in the B-cell/LPS-mediated immune response [ 4 ].…”