Do lampreys have lymphocytes? The Spi evidence

It is generally accepted that living jawless vertebrates (lampreys and hagf ishes) lack the capability of mounting an adaptive immune response. At the same time, however, there are reports describing histological evidence for the presence in agnathan tissues of lymphocytes, the key players in adaptiv e immunity. The question therefore arises whether the cells identified morp hologically as lymphocytes are true lymphocytes in terms of their genetic: developmental program. In this study, evidence is provided that the lamprey s express a member of the purine box 1 (PU.1)/spleen focus-forming virus in tegration B (Spi-B) gene family known to be critically and specifically inv olved in the differentiation of lymphocytes in jawed vertebrates. The lampr ey gene is expressed in the lymphocyte-like cells of the digestive tract an d inexplicably also in the ovary.