Antigen-initiated B-lymphocyte differentiation. VIII. Sedimentation velocity and buoyant density characterization of virgin antibody-forming cell progenitors in the adoptive immune response of unprimed CBA mice to 4-hydroxy-3-iodo-5-nitrophenylacetic acid-polymerized bacterial flagellin antigen.

Abstract

The characteristics of antibody-forming cell (AFC) progenitors lacking previous contact with specific antigen (virgin AFC progenitors) has been studied using sedimentation velocity and buoyant density separation for the investigation of physically distinct B-cell subpopulations. Functional characterization of isolated subsets was made using a quantitative adoptive immune assay for the IgM AFC progenitors responding to the antigen 4-hydroxy-3-iodo-5-nitrophenylacetic acid conjugated polymerized bacterial flagellin. Extensive heterogeneity is present among B lymphocytes, only some subpopulations of which exhibit AFC progenitor function. In the spleen of adult conventional CBA mice, atypically fast sedimenting cells of low buoyant density are active, while typical small B lymphocytes do not appear to be progenitors of IgM AFC. Spleen of adult specific pathogen-free (SPF), germfree, and athymic nude mice give similar results, although a minor population of typical slowly sedimenting dense cells are active in the latter two sources. Adult conventional bone marrow cells are as physically and functionally heterogeneous as splenic B cells, and although a significant proportion of AFC progenitor activity is found among dense, slowly sedimenting cells, most of the activity is among low density, faster sedimenting cells. In contrast to this situation in adult animals, where most of the unprimed AFC progenitors are large, atypical B cells, the spleens of neonatal mice provide a site where virgin AFC progenitors with the physical properties of typical small B lymphocytes are found. While being present in conventional and SPF neonatal spleens, these virgin cells are predominant in 7-day-old germfree mouse spleen. These findings suggest that the newborn virgin B cell is a typical small lymphocyte. However, few cells of this type are found in the adult animal. The unprimed AFC-progenitor population in the adult consists of large, fast sedimenting, low buoyant density, adherent cells, the physical properties of which are characteristic of activated B lymphocytes. It is suggested that these atypical cells are derived from the small newborn virgin B cell by the nonspecific effects of environmental antigenic stimuli.

Tolerance to a Reactive Hapten. Differential Susceptibility of B Cell Subsets and Mechanism of Induction

“…However, it is of particular significance that a subpopulation of immature B cells exhibiting a high level of tolerance susceptibility is present in the spleens of adult mice. The B lymphocyte heterogeneity detected here in adult spleen is supported by recent studies oJ the B cell differentiation pathway , Shortman et al 1976). The coexistence in adult spleen of both mature adult-type B cells and immature, neonatal-type B lymphocytes is not unexpected, since the spleen can assume the total burden of B cell production in the adult mouse deprived of marrow function (Phillips & Miller 1974).…”

Murine Models of Tolerance Induction in Developing and Mature B Cells

“…B-cell subpopulations have also been assessed previously by a variety of other markers such as cell density and size (La Fleur et al 1972, Strober 1975, Fidler et al 1976, Press et al 1977, Ig receptor turnover (Melchers et al 1975), differences in generation time (Strober 1975), response to mitogens (Melchers et al 1975, Melchers 1977. susceptibility to anti-idiotype and anti-immunoglobulin suppression (Raff et al 1975, Sidman & Unanue 1975, Strayer et al 1975, Bruyns et al 1976, Kearney etal.…”

A revisionist history of adult marrow stem cell biology or ‘they forgot about the discard’

“…These cells appeared more differentiated than CFU-S and were in a higher proliferative state. There followed a steady stream of descriptions of in vitro assays for progenitors with different lineage potentials; erythroid, 6 megakaryocyte, 7 mast cell, 8 eosinophil, 9 T cell 10 and B cell, 11 and then more primitive progenitors termed blast forming units and progenitors with multilineage potentials. 12,13 Eventually progenitors with virtually every possible mix of hematopoietic cells were described with multilineage ‘primitive’ progenitors responding to multiple cytokines and with more restricted progenitors responding to fewer cytokines and finally with unilineage progenitors responding to single cytokines.…”