3. B-cell ontogeny

chains contains a short hydrophobic stretch which spans the lipid bilayer of the

sIgs play a complementary role to that of T-cells. It needs to use other mechanisms for antigen removal. This implies that they bind other molecules, like complement molecules, or specialized receptors, called Fc receptors (FcRs, receptors of fragment crystallizable region), on the surface of effector cells that

Antibodies allow B-cells to provide systemic protection of the host and immune surveillance through pathogen recognition and organization of immune reactions. Their expression varies according to the state of differentiation of B-cells. After activation, B-cells transform into plasma cells that secrete antibodies

transported rapidly throughout the body by blood or lymph or secreted through the epithelia to protect the interface between the body and its environment. IgG antibodies also provide a mechanism by which acquired immunity can be transmitted from the mother to the fetus or infant, thus providing acquired immune protection during the critical period of early life. Nevertheless, some antibodies can bind to self-structures, referred to as autoreactive antibodies, and induce, under certain conditions, aberrant immune responses and tissue

Human FcRs and their cell localization and immune functions. DCs, dendritic cells; FcRn, neonatal fc receptor; FcRs, receptors of fragment crystallizable region; FDCs, follicular dendritic cells; Fl58, phenylalanine at position 158; GC, germinal center; H131, histidine at position 131; ICs, antigen-antibody immune complexes; PIgR, polymeric immunoglobulin receptor; R131, arginine at position 131; V158, valine at position 158.

of the same specificity as their membrane BCR. Secreted antibodies are

membrane [26] (Figure 4).

Normal and Malignant B-cell

damage [28].

Figure 5.

10

they activate, including phagocyte cells (Figure 5).

The differentiation of B-cells from hematopoietic stem cells into pro-B, then pre-B, then immature B-cells, and finally into mature B-cells is characterized by several events, including (i) modification of membrane differentiation markers; (ii) Ig gene rearrangement, which takes place at the pro-B and pre-B stages, allowing the expression of BCR; and (iii) negative clonal selection.
