PRELI, the human homologue of the avian px19, is expressed by germinal center B lymphocytes

We report the identification of a human cDNA encoding a 25 kDa protein of r elevant evolutionary and lymphoid interest (PRELI), PRELI was cloned by scr eening a B lymphocyte-specific cDNA library with a probe generated by mRNA differential display. PRELI amino acid sequence is 85% similar to the avian px19 protein, expressed within the blood islands and in the liver during a vian embryo development. PRELI and px19 contain tandem repeats (A/TAEKAK) o f the late embryogenesis abundant (LEA) motif, characteristic of a group of survival molecules and originally thought to be present only in plant prot eins. Interestingly, PRELI expression is high in the fetal liver, a major s ite for B cell lymphopoiesis, while the mRNA levels in other fetal tissues such as the brain, lung, and kidney are comparatively low. At the adult sta ge, PRELI expression is drastically reduced in the liver but exhibits high mRNA levels in the spleen, brain, lung and kidney tissues, suggesting that PRELI expression may be important for the development of vital and immunoco mpetent organs. Moreover, PRELI is also highly expressed in the adult lymph nodes and peripheral blood leukocytes, further stressing that at the adult stage, PRELI expression may be important during secondary immune responses . Consistent with this hypothesis, the expression of PRELI is predominant w ithin germinal centers (GC), a stage in which B lymphocytes are under a str essful selection pressure, Taken together these data: (i) strongly support the notion that the conserved LEA motif represents a phylogenetic link betw een plants and animals, (ii) reveal a novel molecule whose expression may p lay a role in the maturation of distinct human tissues, and (iii) suggest t hat PRELI expression may be important for GC B lymphocytes.