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Jawless fishes occupy a critical phylogenetic position in understanding the origin of the adaptive immune system. Here, we performed large-scale expressed sequence tag analysis of leukocytes isolated from the inshore hagfish Eptatretus burgeri. Although we found many immunity-related genes such as those involved in lymphocyte or hematopoietic cell signaling and development as well as cytokine and cytokine receptor genes, MHC molecules or antigen receptors were not identified. We characterized two hagfish cDNAs that closely resembled mammalian proteins with essential roles in adaptive immunity, one encoding a GATA3-like molecule and another encoding a Bruton''s tyrosine kinase (Btk)-like molecule. The GATA3-like gene of hagfish was equidistant from GATA3 and GATA2 in jawed vertebrates. Similarly, the hagfish Btk-like molecule was not Btk itself, but qualified as a pre-duplicated form of Btk and Bmx in jawed vertebrates. In total, our work provides circumstantial evidence that adaptive immunity is unique to jawed vertebrates. [Copyright &y& Elsevier]

Meriones unguiculatus commonly known as gerbils are widely used as animal models for a variety of parasitic infections such as Brugia malayi, Entamoeba histolytica, Giardia duodenalis, Toxoplasma gondi, Helicobacter pylori, Strongyloides stercoralis and Echinococcus multilocularis. Groups of BALB/c mice, gerbils and XID mice were studied for antibody responses to T-independent antigens. Gerbils were found to be significantly deficient in eliciting antibodies to both dextran and phosphorylcholine (PC) in comparison to BALB/c mice. The antibody response of gerbils to T-independent antigens was found to be similar to the response observed in Bruton''s tyrosine kinase (Btk) deficient XID mice, which are known to be poor responders to T-independent antigens. Similar to XID mice, normal gerbil sera were found to be deficient in naturally occurring antibodies to single stranded DNA (SS-DNA), lipopolysaccharide (LPS) and phospholipids. This raises the possibility of a deficiency of CD5+ B-lymphocytes (also known as B-1 cells) in gerbils, since deficiency of this sub-population of B-lymphocytes has been attributed to the absence of such naturally occurring antibodies in XID mice. These results indicate the need to study immunogenicity of parasite T-independent antigens and their relationship to protective immunity in parasitic infections in gerbils. [Copyright &y& Elsevier]