Protection from CMV infection in immunodeficient hosts by adoptive transfer of memory B cells.

Severe disease associated with cytomegalovirus (CMV) infection is still a major problem in patients who undergo transplantation. Support of the patients' immune defense against the virus is a major goal in transplantation medicine. We have used the murine model of CMV (MCMV) to investigate the potential of a cell-based strategy to support the humoral antiviral immune response. Immunocompetent C57BL/6 mice were infected with MCMV, and memory B cells from the immune animals were adoptively transferred into T-cell- and B-cell-deficient RAG-1(-/-) mice. Following MCMV infection, a virus-specific IgG response developed within 4 to 7 days in the recipient animals. Concomitantly, a significant reduction in viral titers and DNA copies in several organs was observed. In addition, the memory B-cell transfer provided long-term protection from the lethal course of the infection that is invariably seen in immunodeficient animals. Transfer of memory B cells was also effective in protecting from an already ongoing viral infection, indicating a therapeutic potential of virus-specific memory B cells. T cells were not involved in this process. Our data provide evidence that a cell-based strategy to support the humoral immune response can be effective to combat infectious pathogens in severely immunodeficient hosts.

Activation of virus-specific memory B cells in the absence of T cell help.

Humoral immunity is maintained by long-lived plasma cells, constitutively secreting antibodies, and nonsecreting resting memory B cells that are rapidly reactivated upon antigen encounter. The activation requirements for resting memory B cells, particularly the role of T helper cells, are unclear. To analyze the activation of memory B cells, mice were immunized with human cytomegalovirus, a complex human herpesvirus, and tick-born encephalitis virus, and a simple flavivirus. B cell populations devoid of Ig-secreting plasma cells were adoptively transferred into T and B cell-deficient RAG-1-/- mice. Antigenic stimulation 4-6 d after transfer of B cells resulted in rapid IgG production. The response was long lasting and strictly antigen specific, excluding polyclonal B cell activation. CD4+ T cells were not involved since (a) further depletion of CD4+ T cells in the recipient mice did not alter the antibody response and (b) recipient mice contained no detectable CD4+ T cells 90 d posttransfer. Memory B cells could not be activated by a soluble viral protein without T cell help. Transfer of memory B cells into immunocompetent animals indicated that presence of helper T cells did not enhance the memory B cell response. Therefore, our results indicate that activation of virus-specific memory B cells to secrete IgG is independent of cognate or bystander T cell help.

Cooperative binding of Sox10 to DNA: requirements and consequences.

The high-mobility-group (HMG) domain containing transcription factor Sox10 is an important regulator of various processes including the development of neural crest cells and glial cells. Target gene promoters contain multiple Sox10-binding sites, which either support monomeric or cooperative, dimeric binding. The latter is unusual for Sox proteins and might contribute to functional specificity of Sox10. We find that specific amino acid residues in a conserved region immediately preceding the HMG domain of Sox10 are required for cooperative binding. These residues cooperate with the HMG domain during dimeric binding in a manner dependent on specific determinants within the first two alpha-helices of the HMG domain. Cooperativity of DNA binding is surprisingly refractory to changes in the overall conformation of the DNA-bound dimer. Whereas maintenance of cooperativity is essential for full activation of the promoter of the myelin protein zero target gene, dimer-dependent conformational changes such as the exact bending angle introduced into the promoter appear to be less important, shedding new light on the architectural function of Sox proteins.