B-cell subsets and the mature preimmune repertoire. Marginal zone and B1B cells as part of a "natural immune memory"

The rate of elimination of a pathogenic agent is of critical importance for the host and determines the extent and consequences of the infection. Anti body production. along with the activity of other cells of the immune syste m. plays an important role early and late in the response and contributes t o all containment and elimination of the organism. B-cell clones reaching t he mature long-lived pool are heterogeneous: some belong to thle B1 B-cell subset, some an: enriched in the CD21(high) compartment (mostly marginal to ne (MZ)), whereas others recirculate primarily among the B-cell follicles ( FO). This segregation is a T-independent. CD40L-independent bur BCR/CD 19-d ependent process. Antigen encounter will recruit antigen-specific cells fro m the pool of mature B-lymphocytcs and activate them to perform effector fu nctions. CD21(high)CD23(low) B cells enriched in the MZ of the spleen initi ate the early plasmablast wave during the first 3 days of an antibody respo nse against particulate T-independent bacterial antigens. These findings in dicate a functional heterogeneity within the mature B-lymphocyte population . MZ B cells and B1 B, in contrast to FO B cells, have the unique capacity to generate effector cells in early stages of the immune response against ( particulate) antigens that are scavenged efficiently in these specialized a natomical sites.