3.2 Phases of B-cell ontogeny: antigen-dependent and antigen-independent

B-cell ontogeny can be separated into two main phases: earlier antigenindependent phase and later antigen-dependent phase (Figure 6). It should also be recalled that thymus-independent (TI) antigens have the ability to stimulate B-cells without T-cells' help and are traditionally divided into two categories, TI-1 antigens that can activate B-cells through coengagement of Toll-like receptors (TLR), such as LPS or other bacterial polysaccharides, and TI-2 antigens that lead to extensive cross-linking of the BCR, such as polymeric protein antigens or repeated structural motifs [33]. Some antigens fall outside these and form a third category. Finally, T-cell-independent responses should be discussed, knowing that T-cells could intervene at different levels of B-cell development in response to TI antigens (For review, see [34–36]).
