Paul W. Kincade

Formation of B Lymphocytes in Fetal and Adult Life

Publisher Summary were regarded Lymphoid and hematopoietic stem cells are highly specialized and antigens recently identified by several laboratories may be useful in resolving categories and stages of differentiation. This chapter discusses some procedures that may not only allow the differentiative potential of B-cell precursors to be assessed but provide some insight into the inductive signals and regulatory mechanisms involved. The extraordinary progress of experimental hematologists in resolving the precursors of erythroid and myeloid cells has created a false sense of understanding about the nature and fate of stem cells relevant to the humoral immune system. The time when B cells or their precursors first appear during ontogeny or during regeneration of irradiated animals, they are diluted among nonlymphoid hematopoietic cells. The use of cytoplasmic immunoglobulin as a marker for pre-B cells and various cell surface antigens are discussed. Cells dissected from spleen colonies have been used to restore humoral immunity to irradiated secondary recipients, and the time required was because of transition of stem cells. Extensive examinations of spleen colonies have not revealed any that had predominantly lymphoid morphology. However, the possibility of a minor entry of stem cells into B and T pathways would be difficult to rule out, particularly if the newly formed cells rapidly migrated elsewhere.

B-lymphocyte precursors in immunodeficient, autoimmune and anemic mice.

There are now several promising approaches to understanding B-lymphocyte heterogeneity and development. Among these is the use of monoclonal antibodies directed to cell surface antigens. Appropriate reagents are available for identifying cells in embryonic and adult murine hemopoietic tissues which are destined to quickly become functional B cells. This makes it possible to enumerate and manipulate such precursors before placing them in culture or an appropriate recipient animal where their further maturation can occur. One immediate application of these methods is to the study of animal models where genetic defects influence development ofthe humoral immune system. These are likely to reveal new cell types and functions that are critical to B-cell formation and provide examples of compensatory changes which can take place in response to primary immunological lesions. The purpose of this article will be to summarize our recent observations on the incidence and nature of B-cell precursors in several well-studied strains of mice which have abnormalities affecting humoral immunity.

Colony-forming b cells in f1 hybrid and transplanted cba/n mice.

Abstract B lymphocytes which form colonies in semisolid cultures were assayed in the F 1 progeny of mutant CBA/N and wild-type CBA/H mice. Male offspring of CBA/N mothers had no clonable B cells, and their heterozygous female litter-mates had approximately half the incidence and total number of colony-forming cells found in age-matched normal CBA/H females. Normal and defective mice were lethally irradiated and grafted with hemopoietic cells from either normal or CBA/N mice. Recipients of CBA/N cells did not regenerate B cells which function in the cloning assay, whereas colony-forming cells returned to a normal incidence in all mice grafted with normal cells. Cytogenetic analysis confirmed that the clonable B cells in reconstituted CBA/N mice were derived from donor CBA/H-T6T6 cells. Newborn CBA/N mice had normal numbers of immunoglobulin-bearing cells, and these subsequently acquired Ia antigens. However, these B cells did not expand to the numbers found in the spleens of normal adult mice. These findings confirm and extend earlier studies of immunodeficient CBA/N mice and suggest that a mutation of a single X-chromosome-borne gene affects the production and/or functional capability of at least one category of virgin B lymphocytes.

Apparent differences in B-lineage differentiation occurring in fetal and adult life.

B-lymphocytes first appear in fetal liver and spleen of mammalian embryos whereas bone marrow is the principal site for their formation in adults. Studies of embryos and neonates provide a unique perspective on early events in B-lymphocyte differentiation, but there is reason to suspect that there may be fundamental differences in the fetal and adult models. Not only do populations of B-cells in fetal/neonatal tissues differ from those which predominate in adult marrow and spleen but recent observations indicate that the immediate precursors of B-cells in these tissues may differ as well. Expression of cell surface IgD (sIgD) coincides with acquisition of “adult” characteristics by the humoral immune system and the general question of whether B-cells are formed through similar processes in fetal and adult life can be considered in that context.

DIFFERENCES IN THE CELL SURFACE PHENOTYPE OF NORMAL AND LEUKEMIC PRE-B CELLS

ABSTRACT Two monoclonal rat antibodies which were developed against a murine B lymphoma cross-reacted with human hemopoietic cells. In both species the antibodies were specific for lymphoid cells in normal marrow and included all recognizable cμ + , sIg − “pre-B” cells. Human pre-B cell lines were not stained by these antibodies. Initial observations suggest that pre-B ALL cells from pretreatment patients may also fail to stain with these antibodies. Possible reasons for this apparent difference in surface antigen representation are discussed.