טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentZaretsky Irina
SubjectThe Role of Vav2 in B Cell Development and TLR-Mediated
Responsiveness
DepartmentDepartment of Medicine
Supervisor Professor Doron Melamed
Full Thesis textFull thesis text - English Version


Abstract

The proto-oncogene Vav family contains three proteins that act as guanine-nucleotide exchange factors and affect diverse cellular responses, such as the regulation of gene transcription and cytoskeleton rearrangements in B cells. Several previous studies have shown that Vav proteins are necessary for B cell development beyond the immature stage as well as for mature B cells responses following their TLR4 mediated activation with LPS. However the role of Vavs in immature B cell TLR-mediated responsiveness has not been investigated.

In this work we studied whether Vav2-/- protein deficiency may influence normal B cell development and responsiveness to appropriate TLR signals in the bone marrow using our bone marrow culture system. First FACS analysis presented normal maturation of Vav2 deficient BM B cells and analysis of RAG2 expression by RT-PCR and kappa/lambda ratio by FACS, showed that immature B cells from Vav2-/- mice also undergo normal receptor editing confirming that the absence of Vav2 had no significant influence on B cell development and maturation.

We also found that after stimulation with LPS or CpG-DNA, MTT and CFSE assays showed no significant differences in immature B cell viability and proliferation between normal and Vav2 deficient mice. ELISPOT and ELISA analysis revealed that Vav2 knockout had no impact on antibody production and secretion by BM B cells. In addition, immature B lymphocyte ability to undergo Ig switch recombination remained intact despite the absence of Vav2 protein. Thus we concluded that Vav2 deficiency had no effect on immature B cells upon TLR4/RP105 activation by LPS or TLR9 activation by CpG-DNA. 

Furthermore, Vav2 absence has no influence on mature B cell responsiveness upon TLR4 activation as it was described by M. Turner in 2005 (Turner et. al. 2005) and in our work we proved normal mature B cell responsiveness upon TLR9 activation in Vav2-/- mice.

Our results have shown that although there is strong evidence of a role for Vav proteins in the signal transduction via BCR and via TLRs, the absence of Vav2 had no significant influence B cell development, maturation and TLR-mediated responsiveness presumably due to the compensational capability of VAV1 and VAV3 isoforms or other functional proteins in B cells.