| First Author | Kuraoka M | Year | 2009 |
| Journal | J Immunol | Volume | 183 |
| Issue | 5 | Pages | 3237-48 |
| PubMed ID | 19667096 | Mgi Jnum | J:151852 |
| Mgi Id | MGI:4355448 | Doi | 10.4049/jimmunol.0901548 |
| Citation | Kuraoka M, et al. (2009) Activation-induced cytidine deaminase expression and activity in the absence of germinal centers: insights into hyper-IgM syndrome. J Immunol 183(5):3237-48 |
| abstractText | Somatic hypermutation normally occurs as a consequence of the expression of activation-induced cytidine deaminase (AID) by Ag-activated, mature B cells during T cell-dependent germinal center responses. Nonetheless, despite their inability to express CD154 and initiate GC responses, patients with type 1 hyper-IgM syndrome (HIGM1) support populations of IgM(+)IgD(+)CD27(+) B cells that express mutated Ig genes. The origin of these mutated B cells is unknown; the IgM(+)IgD(+)CD27(+) cells do not express AID and appear to acquire mutations independent of stringent selection by Ag. Here, we demonstrate that immature/transitional 1 B cells from the bone marrow of CD154-deficient mice express AID and acquire Ig mutations that lack the hallmarks of antigenic selection via BCR signaling. Comparable levels of AID expression was found in developmentally immature B cells recovered from murine fetal liver and from human immature/transitional 1 B cells recovered from umbilical cord blood. AID expression in human fetal liver was also robust, approaching that of human tonsil tissue and the human germinal center B cell line, Ramos. These observations led us to conclude that AID expression in developing human B cells is the origin of the mutated IgM(+)IgD(+)CD27(+) B cells present in HIGM1 patients, and we propose that both mice and humans share a latent, AID-dependent pathway for the preimmune diversification of B lymphocytes that is more prominent in chicken, sheep, and rabbits. |
