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PubMed1976

B cell ontogeny in rabbits. Immunofluoresecent localization of B cells in fetal and neonatal rabbits.

The mammalian equivalent of the Bursa of Fabricius, the organ responsible for B cell maturation in avian species, has not been identified despite anatomic and ablative studies which suggest that the gut-associated lymphoid tissues (GALT) subserve this function. By analogy to the Bursa, the mammalian organ directing B cell ontogeny should be the site where IgM-bearing cells (B cells) are first identifiable. In this study, fluorescein-tagged heavy chain specific antirabbit IgM is used to localize initial sites of B cell appearance in rabbit fetal and neonatal lymphoid tissues. IgM-bearing cells are found 2 days before birth in the thymus and 1 day before birth in GALT. Immunoglobulin-bearing cells in spleen, lymph node, and bone marrow are undetectable until after birth. B cells bearing the IgM marked precede the appearance of IgG-bearing cells by 1 to 4 days in all instances. Intraperitoneal implantation of Millipore chambers containing immature fetal thymic tissue into neonatal hosts reveals that in situ development of IgM cells takes place independent of host cell traffic. The results suggest that B cell ontogeny in mammals is more complex than in avian species and demonstrates probable involvement of the thymus in the maturational process.

Animals↗
PubMed1979

Studies on B-cell memory. II. T-cell independent antigen can induce B-cell memory.

Both athymic nude mice and normal mice primed with a T-cell independent antigen, i.e. dinitrophenylated dextran (DNP-DE), at a sub-immunogenic dose, produced very poor anti-DNP responses to a later challenge with the same antigen. B-cell memory was expressed, however, as an enhanced IgM response after the challenge of the DNP-DE-primed mice with the T-cell dependent antigen (dinitrophenylated haemocyanin, DNP-KLH) in the presence of functional T-cells. Moreover, DNP-DE-primed spleen cells also revealed an enhanced IgM response after adoptive transfer into irradiated recipients and challenge with DNP-DE. The injections of DNP-DE-primed nude mouse serum into unprimed mice resulted in the reduction of anti-DNP response to the immunization with DNP-DE. These results indicate that (a) T-cell independent DNP-DE causes the differentiation of B cells not only into antibody-forming cells but also into memory cells, (b) these memory cells can be triggered in situ by the T-cell dependent DNP-KLH in the presence of helper T cells but not by T-cell independent antigen, and (c) some humoral factor(s) induced by DNP-DE-priming seems to interfere with the expression of B-cell memory only when challenged with T-cell independent DNP-DE.

Animals↗
PubMed1977

Frequencies of mitogen-reactive B cells in the mouse. II. Frequencies of B cells producing antibodies which lyse sheep or horse erythrocytes, and trinitrophenylated or nitroiodophenylated sheep erythrocytes.

The B-cell mitogens LPS and lipoprotein stimulate 20-35 percent of all B cells in the spleen of 6- to 8-wk old C3H/Tif mice, as determined by limiting dilution analysis of precursors. Each reactive cell grows to a clone of IgM-secreting PFC, enumerated in a hemolytic plaque assay detecting all IgM secreting cells, regardless of v-region specificity. We have used these mitogens to reveal the total repertoire of Ig specificities produced by these mitogen-reactive B cells. We have determined in plaque assays with six different target erythrocytes the number of spleen cells limiting to one the number of mitogen-reactive B cells detected as specific IgM-secreting clones in each of these plaque assays. By this method, the absolute frequencies of precursor B cells with defined v-gene specificities could be calculated, for at least, one third of all B cells. The frequencies of specific IgM-plaque-forming B-cell clones within the total pool of mitogen-reactive B cells was 1 in 10 for NIP(12),-SRC, 1 in 50 for TNP(12)- SRC, 1 in 100 for NIP(1)-SRC, 1 in 160 for TNP(3)- SRC, 1 in 500 for HRC, and 1 in 1,000 for SRC. These frequencies were the same in the LPS- and in the lipoprotein-reactive B-cell population for TNP(30)- SRC and SRC.

Animals↗
PubMed1979

T-helper function of parent leads to F1 chimeras. Presence of a separate T-cell subgroup able to stimulate allogeneic B cells but not syngeneic B cells.

Parent leads to F1 chimeras were prepared by reconstituting sublethally irradiated H-2 heterozygous mice with marrow cells from one parental strain. Purified parental strain T cells prepared from unprimed chimeras were exposed to sheep erythrocytes in heavily irradiated mice of each of the two parental strains and recovered from thoracic duct lymph of the recipients at either day 1 or day 5 posttransfer. The lymphoborne cells were then tested for their capacity to collaborate in vivo with B cells of the two parental strains. From this approach it was concluded that parent leads to F1 chimera T cells contain two discrete subgroups of T-helper cells, one specific for self H-2 determinants and the other restricted to H-2 determinants of the opposite parental strain. The restrictions mapped to the K-end of the H-2 complex.

Animals↗
PubMed1979

Localization of spontaneously hyperactive B cells of NZB mice to a specific B cell subset.

NZB mice produce numerous autoantibodies and have a subpopulation of B cells characterized by marked spontaneous hypersecretion of IgM. The latter trait is determined by autosomal genes, in F1 hybrids of NZB and normal strains. We tested the hypothesis that the hypersecreting B cells of NZB mice are contained within a specific subpopulation by examining (CBA/N X NZB)F1 hybrids. CBA/N mice have an X-linked recessive defect that results in the absence of a functionally distinct B cell subpopulation and impaired antibody responses. The hyperactivity of B cells, characteristic of the NZB parent, was transmitted to the F1 female, but was not expressed by the F1 male, which manifested the CBA/N B cell hyporesponsiveness. By contrast, the NZB xenotropic virus was expressed equally by both male and female F1 mice. We conclude that the NZB B cell abnormality resides within the B cell subpopulation affected by the CBA/N mutation.

Animals↗
PubMed1977

Mechanisms of the adjuvant effect of nystatin on in vitro antibody response of mouse spleen cells: indication of nystatin as a B-cell mitogen and as a stimulant for polyclonal antibody synthesis in B cells.

Adjuvanticity of nystatin, one of the polyenic antifungal antibiotics having as its primary target the membrane sterol of eukaryotic cells, was investigated by examining its effect on several functions of mouse spleen cells relevant to immunological phenomena in vitro. Nystatin was found to stimulate significantly DNA synthesis in thymus-independent (B) cells but not in thymus-dependent (T) cells. Like the other B-cell mitogens such as bacterial lipopolysaccharide (LPS), nystatin elicited nonspecifically polyclonal antibody synthesis in mouse spleen cell cultures, and also restored antibody response of T cell-deficient spleen cells of congenitally athymic nude mice to heterologous erythrocytes (RBC; thymus-dependent antigen). Thus, nystatin and LPS appeared to cause similar changes in the functions of spleen cells relevant to immunological events. However, antagonism but no additive effect in the adjuvanticity was revealed between the two adjuvants. As an interesting finding, the polyclonal generation of anti-RBC antibody-forming cells (AFC) in the spleen cell cultures by stimulation with B-cell mitogen, i.e., either nystatin or LPS, was not inhibited at all by inclusion of any anti-RBC antiserum, whereas, as is well known, the generation of AFC by stimulation with the antigen was specifically suppressed by the corresponding antiserum, indicating a difference in the genesis between the mitogen-induced AFC and the antigen-induced AFC.

Adjuvants, Immunologic↗
PubMed1977

Induction of immunological tolerance requires that the B cells can respond to the polyclonal B-cell-activating properties of the thymus-independent antigens.

Mice were rendered specifically tolerant to the fluorescein isothiocyanatedextran (FITC) epitope by injection of FITC-dextran B512. Their spleen cells were removed at various times and cultivated in vitro with different polyclonal B-cell activators, such as lipopolysaccharide (LPS), purified protein derivative of tuberculin, and native dextran. LPS caused the appearance of high affinity anti-FITC plaque-forming cells to an equal extent with cells from untreated and tolerant animals, whereas native dextran failed to activate cells from tolerant mice, although it was a potent activator of normal cells. It was concluded that tolerance induction only affects those B cells that could respond to the polyclonal B-cell-activating properties of the tolerogen, but not other B cells having an identical set of Ig receptors directed against the tolerogen.

Animals↗
PubMed1978

The role of the thymus for maturation of transferred bursa cells into immunocompetent B cells in chickens treated with cyclophosphamide.

Chickens injected with cyclophosphamide and X-ray irradiated in the newly hatched period were immunized with a mixture of sheep red blood cells, Brucella abortus and Salmonella pullorum at 4, 5 and 6 weeks of age, and were examined for serum antibody titres, serum immunoglobulin concentration and bursal and splenic structures at 7 weeks of age. The neonatal treatments suppressed completely or almost completely antibody responses, immunoglobulin production and formation of bursal follicles and splenic germinal centres. The transplantation of bursa cells into the chickens immunologically impaired by the treatments restored these functions and structures. In contrast, the transfer of bursa cells into chickens thymectomized, cyclophosphamide-treated and X-ray irradiated did not result in efficient restoration of the bursa-dependent immune system; 10-day-old bursa cells hardly restore the system, although 4-week-old bursa cells did so slightly. The chickens thymectomized, cyclophosphamide-treated, X-ray irradiated and repopulated with 10-day-old bursa cells were examined for the existence of functional B cells with the use of a syngeneic cell transfer system. The experiments verified that immunocompetent B cells had not developed in the chickens thus treated.

Animals↗
PubMed1979

Role of adherent T cells and of B cells in the immune response to purified protein derivative of tuberculin.

The role of monocytes, B cells, and adherent and nonadherent T cells in the response of purified protein derivative of tuberculin (PPD) as measured by [3H]thymidine uptake in vitro has been explored. The response to PPD was found to be highly dependent on monocytes, to approximately the same extent as previously found for the responses to concanavalin A (Con A) and phytohemagglutinin. The response to PPD was also found to be highly dependent on a population of adherent T cells different from the adherent T cell population involved in the response to Con A. In the case of PPD, the effect was additive, as opposed to the potentiating effect seen for Con A. Further, the adherent T cells involved in the response to PPD were much more sensitive to hypotonic shock than those in the response to Con A. B cells were also found to be important in the response to PPD, although only to a slight extent.

B-Lymphocytes↗
PubMed1977

In vitro tolerance induction of neonatal murine B cells as a probe for the study of B-cell diversification.

The susceptibility to in vitro tolerance induction has been implicated as a characteristic of B cells early in their development, since DNP-reactive B cells are tolerizable only during the first days after birth, and 25% of adult bone marrow cells are tolerizable. In the present study, a modification of the in vitro splenic focus technique was utilized to determine if PC-specific B cells, by virtue of their late expression (approximately 1 wk post-parturition), also display susceptibility to tolerance induction. The results demonstrate that at 7-10 days after birth, when over 90% of the DNP-specific splenic B cells are resistant to tolerance induction, the majority of PC-specific B cells are tolerizable. These results re-emphasize tolerance susceptibility as a characteristic of developing clones, confirm the late acquisition of PC-specific B cells, and support the contention that the acquisition of the specificity repertoire is a highly ordered, specifically predetermined process which is independent of antigen-driven events.

Animals↗
PubMed1976

Genetic control of B-cell responses. II. Identification of the spleen B-cell defect in C3H/HeJ mice.

The responsiveness of spleen cells from C3H/HeJ and C3H/Tif mice to lipopolysaccharide (LPS) was compared. Around 1,000-fold higher concentration of LPS were required to minimally activate HeJ cells, as compared with Tif high-responder cells, to both proliferation and polyclonal antibody secretion. However, HeJ cells did respond to higher LPS concentrations (100 and 1000 mug/ml). This selective pattern of responsiveness to LPS was also observed in the polyclonal responses of strains to LPS in vivo. Furthermore, the unresponsiveness of HeJ spleen cells was found to depend on a pure B-cell defect in the capacity to interact and/or generate triggering signals on interaction with LPS. Thus, adherent cells, thymus-derived lymphocytes, serum factors, and other non-specific conditions inherent in spleen cell suspensions of low-responder mice were not responsible for suppressing a putative B-cell response to LPS. The present findings are compatible with the possibility that the defect in C3H/HeJ B cells reflects the absence of a structure on the cell surface membrane that is functionally responsible for mediating LPS triggering.

Animals↗
PubMed1979

Induction of secretion of IgM from cells of the B cell line 38c-13 by somatic cell hybridization.

Cells of the murine B cell line 38C-13 possess immunoglobulins of the IgM class on their surface but do not secrete them. Upon hybridization of 38C-13 cells with murine myeloma cells, hybridoma clones were obtained that secreted both pentameric IgM of 38C-13 origin and the myeloma protein. All hybridoma clones synthesized and secreted large amounts of homogeneous IgM with a half disappearance time of about 2 hr, typical of mature plasma cells. Concomitantly with the induction of IgM secretion, the hybridoma cells lost their surface IgM. The possibility of separate pathways for the synthesis of membrane and secreted IgM is discussed.

Animals↗