七鳃鳗和八目鳗（最后的无颌类脊椎动物）之所以吸引免疫学家注意，是因为它们的适应性免疫系统在灵活性上可与人类的相媲美。在人类身上，每个淋巴细胞表达针对某一种抗原的预期性受体，由可变的、多样的连接片段构成。无颌类脊椎动物利用由“富含亮氨酸重复序列”的蛋白片段组成的可变淋巴细胞受体，并有一个不可变的柄系在淋巴细胞表面上。
对海生七鳃鳗所做的新的研究工作显示了更多与人类相似的地方：它们有一个分成不同腔室的适应性免疫系统，含有与哺乳动物适应性免疫系统中分泌细胞因子的T-细胞及分泌抗体的B-细胞相似的细胞。这表明，淋巴细胞分化沿类似T-细胞和B-细胞系方向上所发生的分歧在演化上出现的时间要比人们以前所认为的早得多，因而它们的系统不是我们人类自己免疫系统的一个先驱，就是同我们自己的免疫系统并行演化的。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 459, 796-801 (11 June 2009) | doi:10.1038/nature08068
Dual nature of the adaptive immune system in lampreys
Peng Guo1,2, Masayuki Hirano1,2, Brantley R. Herrin1,2, Jianxu Li1, Cuiling Yu1, Andrea Sadlonova1 & Max D. Cooper1
1 Emory Vaccine Center and Department of Pathology and Laboratory Medicine, Emory University, 1462 Clifton Road North-East, Atlanta, Georgia 30322, USA
2 These authors contributed equally to this work.
Jawless vertebrates use variable lymphocyte receptors (VLR) comprised of leucine-rich-repeat (LRR) segments as counterparts of the immunoglobulin-based receptors that jawed vertebrates use for antigen recognition. Highly diverse VLR genes are somatically assembled by the insertion of variable LRR sequences into incomplete germline VLRA and VLRB genes. Here we show that in sea lampreys (Petromyzon marinus) VLRA and VLRB anticipatory receptors are expressed by separate lymphocyte populations by monoallelic VLRA or VLRB assembly, together with expression of cytosine deaminase 1 (CDA1) or 2 (CDA2), respectively. Distinctive gene expression profiles for VLRA+ and VLRB+ lymphocytes resemble those of mammalian T and B cells. Although both the VLRA and the VLRB cells proliferate in response to antigenic stimulation, only the VLRB lymphocytes bind native antigens and differentiate into VLR antibody-secreting cells. Conversely, VLRA lymphocytes respond preferentially to a classical T-cell mitogen and upregulate the expression of the pro-inflammatory cytokine genes interleukin-17 (IL-17) and macrophage migration inhibitory factor (MIF). The finding of T-like and B-like lymphocytes in lampreys offers new insight into the evolution of adaptive immunity.
