Characterization of adaptive immune receptors in hagfish (170.13)

Abstract

Abstract Instead of the immunoglobulin based antigen receptors of jawed vertebrates, jawless fish use variable lymphocyte receptors (VLRs) comprised of leucine-rich-repeat (LRR) segments for antigen recognition. Two VLR genes, VLRA and VLRB, have been identified in both lampreys and hagfish. A third VLR, so called VLRC was recently discovered in lampreys. An extensive VLR repertoire is generated through the insertion of diverse LRR sequences into an incomplete germline VLR gene by a gene conversion mechanism. Earlier studies of sea lampreys have shown that VLRB lymphocytes resemble B cells of jawed vertebrates, whereas VLRA lymphocytes are similar to T cells. For the present studies, monoclonal and polyclonal antibodies against the invariant stalk regions of hagfish VLRA and VLRB were produced to identify the VLR-bearing lymphocytes and their products. Flow cytometric analysis indicated that VLRA and VLRB are expressed by separate lymphocyte populations, with VLRA lymphocytes being the dominant population. Western blot and gel-filtration analyses indicated that hagfish VLRB antibodies are released into the circulation as multimeric proteins that are formed by non-covalent linkage of four or five disulfide-bonded VLRB dimers. Conversely, soluble VLRA is not detected in hagfish plasma. These findings indicate that distinctive T-like and B-like lineages are a common feature of the adaptive immune system in both lampreys and hagfish, in keeping with their monophyletic relationship.