B cell development occurs in a series of discrete stages which can be distinguished on the basis of morphologic and functional criteria. Genesis of B cells begins within the fetal liver as early as eight weeks gestation, and is later maintained in bone marrow. The first recognizable developmental stage is the rapidly-dividing pre-B cell which synthesizes cytoplasmic IgM but lacks surface receptors for antigen. Immature B lymphocytes emerging from pre-B cells express surface IgM, but are uniquely susceptible to inactivation as a consequence of specific antigen binding. Progeny of these cells express different classes of cell surface immunoglobulin and become committed to differentiate into plasma cells synthesizing IgM, IgD, IgG, IgA, or IgE immunoglobulins, respectively.
By the beginning of the second trimester, the human fetus has an adult proportion of B lymphocytes expressing different immunoglobulin classes and capable of recognizing an extensive variety of antigens. The qualitative and quantitative deficiencies in antibody responses of newborns, as compared to adults, appear to reflect regulatory interactions with T cells and macrophages rather than absence of B lymphocytes capable of generating a response.
Recent research with recombinant DNA technology has provided remarkable new knowledge of the structure and organization of immunoglobulin genes. This developing information, in concert with more detailed studies of the cellular expression of these genes during ontogeny, holds the promise of generating insights into the molecular mechanisms regulating gene expression during differentation.
- Copyright © 1979 by the American Academy of Pediatrics