Biochemical mechanisms of unresponsiveness and tolerance susceptibility in neonatal splenic B cells
Immunological tolerance depends on the capacity of lymphocytes to exhibit different responses to antigen at different stages of development. B cells that encounter antigen at the mature stage proliferate and differentiate into antibody-secreting cells. In contrast, cells that encounter antigen at the immature stage are rendered unresponsive or killed. We have explored the biochemical basis for this differential responsiveness by comparing the antigen receptor-associated signalling pathways in immature and mature B cells. First, to obtain the highly-purified cells required for biochemical studies, we have developed a new method for isolating B cells from the neonatal mouse spleen. Using such cells, we have examined the expression and activity of tyrosine kinases, critical regulators of antigen receptor signal transduction, at the immature and mature stages of B cell development. These studies have led to the identification of a tyrosine kinase not previously found in mature B cells, p55fgr. In mature cells, fgr is not directly associated with the antigen receptor, but is activated following receptor crosslinking. Interestingly, immature B cells have markedly reduced levels of p55fgr, as well as another src-family tyrosine kinase, p59fyn. Expression of high levels of these kinases during B cell ontogeny coincides with the ability to proliferate in response to receptor crosslinking. These observations suggest that fyn and fgr may be important for mature B cell responses to antigen, and that their absence may contribute to immature B cell unresponsiveness and tolerance susceptibility. In another series of studies, we have examined the ability of accessory signals to modulate immature B cell unresponsiveness. We have found that bacterial lipopolysaccharide, a polyclonal B cell activator, can prolong the survival of immature B cells in culture and overcome their unresponsiveness to antigen receptor stimulation. Together, these studies enhance our understanding of immature B cell unresponsiveness and open up new avenues for exploration of the biochemical mechanisms of B cell tolerance.
Wechsler, Robert Jay, "Biochemical mechanisms of unresponsiveness and tolerance susceptibility in neonatal splenic B cells" (1995). Dissertations available from ProQuest. AAI9532302.