Identification of memory B cells using a novel transgenic mouse model.
Memory B cells help to protect the host from invading pathogens by maintaining persistent levels of Ag-specific serum Ab and generating rapid Ab responses upon re-exposure to Ag. Unambiguous identification of memory B cells has been a major obstacle to furthering our knowledge concerning both the development of B cell memory and secondary Ab responses due to an absence of specific cell surface markers. Germinal centers (GCs) are thought to be the major site of Ig hypermutation and Ag-driven selection of memory B cells. To develop a model that would identify GC-derived memory B cells, we generated transgenic mice that expressed cre recombinase in a GC-specific fashion. Interbreeding these mice with the cre-reporter strain, ROSA26R, produced progeny in which beta-galactosidase (beta-gal) was permanently expressed in B cells of the GC-memory pathway. Analysis following immunization with (4-hydroxy-3-nitrophenyl)acetyl coupled to chicken gamma globulin showed that long-lived beta-gal+ B cells exclusively contained somatically mutated lambda1 V regions and were capable of producing Ag-specific Ab-forming cell (AFC) responses that were >100-fold higher than those afforded by beta-gal- B cells following adoptive transfer to naive hosts. Secondary challenge of immune mice showed that only approximately 20% of secondary AFCs expressed beta-gal. Interestingly, we found that somatic hypermutation of rearranged lambda1 V regions within secondary AFCs showed a strong correlation with beta-gal expression, suggesting that nonmutated B cells contribute significantly to secondary Ab responses. This model should provide useful insights into memory B cell development, maintenance, and differentiation following immunization or pathogenic infection.
Chappell
Craig P
CP
Department of Microbiology and Immunology, Emory Vaccine Center, Emory University, Atlanta, GA 30307, USA.
Jacob
Joshy
J
D000818:Animals; D000941:Antigens; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D001483:Base Sequence; D002454:Cell Differentiation; D004247:DNA / Q000235:genetics; D018858:Germinal Center / Q000166:cytology / Q000276:immunology; D007156:Immunologic Memory; D051379:Mice; D020297:Mice, Congenic; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011506:Proteins / Q000235:genetics; D022661:RNA, Untranslated; D027041:Somatic Hypermutation, Immunoglobulin; D001616:beta-Galactosidase / Q000235:genetics
D000941:Antigens; C110853:Gt(ROSA)26Sor non-coding RNA, mouse; D011506:Proteins; D022661:RNA, Untranslated; D004247:DNA; D001616:beta-Galactosidase