Regulation of human B cell activation by prostaglandin E2. Suppression of the generation of immunoglobulin-secreting cells

The role of prostaglandin E2 (PGE2) in the generation of immunoglobulin-secreting cells (ISC) from human peripheral blood B cells was examined. Initial studies demonstrated that monocyte (M phi)-mediated suppression of the generation of ISC in Staphylococcus aureus (SA)-stimulated cultures was mitigated by indomethacin, and thus suggested that the cyclooxygenase pathway products of arachidonic acid played a role in the regulation of B cell activation. The possibility that PGE2, one of the major products of this pathway generated by M phi-affected human B cell responses, was therefore investigated. PGE2 was found to cause concentration-dependent inhibition of the generation of ISC in pokeweed mitogen- or SA-stimulated B cell cultures supported by T cells. Studies were therefore carried out to determine whether PGE2 inhibited the production of necessary T cell factors or directly altered B cell responsiveness. Initially, the effect of PGE2 on the capacity of mitogen-stimulated cells to secrete a factor that supported the differentiation of B cells into ISC was investigated. Excessive numbers of M phi or PGE2 inhibited the production of B cell differentiation factor from mitogen-stimulated T cells. The effect of PGE2 on the capacity of B cells to differentiate into ISC was more complex. PGE2 inhibited the generation of ISC when B cells were stimulated with SA and B cell differentiation factor-containing T cell supernatants. PGE2-mediated inhibition of ISC generation was observed even when addition of PGE2 was delayed until after ISC first were detected in culture. By contrast, PGE2 caused only minimal inhibition of the generation of ISC cultures stimulated by T cell supernatants alone or protein A-free SA and T cell supernatants. These results suggested that SA-responsive B cells were particularly sensitive to inhibition by PGE2. Additional experiments supported the conclusion that B cell sensitivity to inhibition by PGE2 is augmented by the immunoglobulin cross-linking effects of protein A-containing SA. Overall, the results support the conclusion that PGE2 at physiologically relevant concentrations can influence human antibody responses by means of a direct inhibitory action on the responding B cell or an indirect one on the production of necessary T cell factors.

The roles of T cell factors in activation, cell cycle progression, and differentiation of human B cells

The relationship of the T cell influences involved in human B cell activation and differentiation into immunoglobulin-secreting cells (ISC) was investigated. T cell supernatants (T supt) generated by stimulating T cells with phytohemagglutinin and phorbol myristate acetate contained activities capable of augmenting DNA synthesis and the growth of mitogen-stimulated B cells and supporting the differentiation of ISC. To examine the role of T supt in B cell activation and the progression through the cell cycle, T cell- and monocyte-depleted B cells were stimulated with formalinized Cowan I strain Staphylococcus aureus (SA), and the percentages of cells in G1, S, and G2 + M were determined by acridine orange staining and analysis. In all experiments, a similar percentage of cells entered G1 during the first 24 to 36 hr of culture when stimulated with SA or SA + T supt. Similar results were seen when B cell activation was analyzed by acquisition of a number of other markers of cell activation. Analysis of cell cycle progression with mithramycin staining of cellular DNA in the presence or absence of vinblastine to arrest mitosis indicated that SA-activated B cells were able to complete S and divide in the absence of T supt. Although an effect of T supt on the progression of B cells through the S phase was evident during the first cell cycle, the major effect only became apparent after the first round of cell division. Although T supt was not necessary for initial B cell activation, T cell influences were absolutely necessary for the differentiation of ISC. T supt did not need to be present during the initial 24 to 36 hr of incubation to permit subsequent generation of ISC. However, when T supt was present initially, an increased number of ISC were produced. Hydroxyurea elimination of cells traversing the G1-S interphase indicated that reception of the differentiation signal occurred before the S phase, but that the generation of ISC required subsequent DNA synthesis and/or cell division. Although precursors of ISC were entirely contained within the population triggered to divide by SA alone, there was no preferential expansion of such precursors as a result of SA stimulation. These results indicate that T cell signals are not absolutely necessary for initial B cell activation and progression through the first cell cycle, although T cell factors promote DNA synthesis by some activated B cells. In contrast, differentiation into ISC is completely dependent on T cell influences.(ABSTRACT TRUNCATED AT 400 WORDS)

The roles of T cell factors in activation, cell cycle progression, and differentiation of human B cells

The relationship of the T cell influences involved in human B cell activation and differentiation into immunoglobulin-secreting cells (ISC) was investigated. T cell supernatants (T supt) generated by stimulating T cells with phytohemagglutinin and phorbol myristate acetate contained activities capable of augmenting DNA synthesis and the growth of mitogen-stimulated B cells and supporting the differentiation of ISC. To examine the role of T supt in B cell activation and the progression through the cell cycle, T cell- and monocyte-depleted B cells were stimulated with formalinized Cowan I strain Staphylococcus aureus (SA), and the percentages of cells in G1, S, and G2 + M were determined by acridine orange staining and analysis. In all experiments, a similar percentage of cells entered G1 during the first 24 to 36 hr of culture when stimulated with SA or SA + T supt. Similar results were seen when B cell activation was analyzed by acquisition of a number of other markers of cell activation. Analysis of cell cycle progression with mithramycin staining of cellular DNA in the presence or absence of vinblastine to arrest mitosis indicated that SA-activated B cells were able to complete S and divide in the absence of T supt. Although an effect of T supt on the progression of B cells through the S phase was evident during the first cell cycle, the major effect only became apparent after the first round of cell division. Although T supt was not necessary for initial B cell activation, T cell influences were absolutely necessary for the differentiation of ISC. T supt did not need to be present during the initial 24 to 36 hr of incubation to permit subsequent generation of ISC. However, when T supt was present initially, an increased number of ISC were produced. Hydroxyurea elimination of cells traversing the G1-S interphase indicated that reception of the differentiation signal occurred before the S phase, but that the generation of ISC required subsequent DNA synthesis and/or cell division. Although precursors of ISC were entirely contained within the population triggered to divide by SA alone, there was no preferential expansion of such precursors as a result of SA stimulation. These results indicate that T cell signals are not absolutely necessary for initial B cell activation and progression through the first cell cycle, although T cell factors promote DNA synthesis by some activated B cells. In contrast, differentiation into ISC is completely dependent on T cell influences.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of human B cell proliferation by prostaglandin E2

The role of prostaglandin E2 (PGE2) in the regulation of human B cell proliferation in vitro was examined. Initial studies demonstrated that monocyte (M phi)-mediated suppression of B cell proliferation in Staphylococcus aureus (SA)-stimulated cultures was diminished by indomethacin, and thus it was suggested that cyclooxygenase pathway products of arachidonic acid played a role in the regulation of B cell activation. The possibility that PGE2, one of the major products of this pathway generated by M phi, affected human B cell responses was therefore investigated. PGE2 was found to suppress B cell DNA synthesis and proliferation stimulated by SA in the presence or absence of B cell growth factor (BCGF)-containing T cell supernatants. Suppression was concentration-dependent; significant inhibition was observed in indomethacin-blocked cultures with 10(-10) to 10(-9) M PGE2. In contrast to the effect of PGE2 on SA-induced B cell proliferation, it had minimal effect on pokeweed mitogen (PWM)-stimulated B cell or T cell DNA synthesis. The effect of PGE2 on the generation of BCGF activity from mitogen-stimulated T cells was also examined. PGE2 (10(-7) M) did not inhibit the production of BCGF activity from PWM-stimulated T cells, or from T cells stimulated with the combination of phytohemagglutinin and phorbol myristate acetate. Thus, PGE2 inhibits B cell proliferation in response to SA but not PWM, and has little effect on the production of BCGF by T cells. These results indicate that PGE2 at physiologically relevant concentrations exerts selective regulatory effects on human B cell responses.

Regulation of human B cell proliferation by prostaglandin E2

The role of prostaglandin E2 (PGE2) in the regulation of human B cell proliferation in vitro was examined. Initial studies demonstrated that monocyte (M phi)-mediated suppression of B cell proliferation in Staphylococcus aureus (SA)-stimulated cultures was diminished by indomethacin, and thus it was suggested that cyclooxygenase pathway products of arachidonic acid played a role in the regulation of B cell activation. The possibility that PGE2, one of the major products of this pathway generated by M phi, affected human B cell responses was therefore investigated. PGE2 was found to suppress B cell DNA synthesis and proliferation stimulated by SA in the presence or absence of B cell growth factor (BCGF)-containing T cell supernatants. Suppression was concentration-dependent; significant inhibition was observed in indomethacin-blocked cultures with 10(-10) to 10(-9) M PGE2. In contrast to the effect of PGE2 on SA-induced B cell proliferation, it had minimal effect on pokeweed mitogen (PWM)-stimulated B cell or T cell DNA synthesis. The effect of PGE2 on the generation of BCGF activity from mitogen-stimulated T cells was also examined. PGE2 (10(-7) M) did not inhibit the production of BCGF activity from PWM-stimulated T cells, or from T cells stimulated with the combination of phytohemagglutinin and phorbol myristate acetate. Thus, PGE2 inhibits B cell proliferation in response to SA but not PWM, and has little effect on the production of BCGF by T cells. These results indicate that PGE2 at physiologically relevant concentrations exerts selective regulatory effects on human B cell responses.

The role of B cell proliferation in the generation of immunoglobulin-secreting cells in man

The relationship of B cell proliferation and the generation of immunoglobulin-secreting cells (ISC) was explored in vitro by examining the effect of hydroxyurea (HU), an inhibitor of cellular DNA synthesis, on the generation of ISC from human peripheral blood mononuclear cells (PBM). HU completely inhibited the capacity of PBM to generate ISC in response to pokeweed mitogen (PWM) and other polyclonal B cell activators. Inhibition resulted from an effect on B cell proliferation, because HU also prevented the generation of ISC in cultures of purified B cells supplemented with either T cell supernatants or mitomycin C-treated T cells. Inhibiting B cell proliferation by treating them with mitomycin C before culture also abolished the generation of ISC. When ISC were enumerated after a 7-day incubation with PWM, the addition of HU as late as day 6 of culture was found to inhibit responsiveness markedly. This suggested that those cells that had acquired the capacity to secrete lg were actively dividing, and continued division was necessary for ongoing lg secretion. To examine this possibility, experiments were carried out in which responsiveness was assayed on a daily basis. ISC could be detected after a 3- or 4-day incubation and reached maximum at day 6 or 7. Addition of HU on days 3 to 7 caused a highly significant reduction in the number of ISC within 24 hr. ISC did not begin to show resistance to the effects of HU until later in culture. This observation supported the conclusions that ISC were a rapidly cycling cell population and that ongoing lg secretion, as well as expansion in the number of ISC, depended on continued proliferation of the ISC. To confirm directly that ISC were a cycling cell population, PBM were cultured with PWM for 6 days, fixed, stained for both cytoplasmic lg and DNA content, and analyzed on the fluorescence-activated cell sorter. This method made it possible to quantitate the DNA content of individual lg-synthesizing cells and thus to determine their position in the cell cycle. As many as 40% of cytoplasmic lg-positive cells were found to be in the S, G2, or M phases of the cell cycle. These data indicate that ISC generated in man after in vitro stimulation with a number of polyclonal activators are not stable terminally differentiated lg-secreting plasma cells but rather an actively cycling lg-secreting population. Furthermore, the results indicate that proliferation of the ISC themselves plays an important role in determining the magnitude of the resultant antibody response.

The role of B cell proliferation in the generation of immunoglobulin-secreting cells in man

The relationship of B cell proliferation and the generation of immunoglobulin-secreting cells (ISC) was explored in vitro by examining the effect of hydroxyurea (HU), an inhibitor of cellular DNA synthesis, on the generation of ISC from human peripheral blood mononuclear cells (PBM). HU completely inhibited the capacity of PBM to generate ISC in response to pokeweed mitogen (PWM) and other polyclonal B cell activators. Inhibition resulted from an effect on B cell proliferation, because HU also prevented the generation of ISC in cultures of purified B cells supplemented with either T cell supernatants or mitomycin C-treated T cells. Inhibiting B cell proliferation by treating them with mitomycin C before culture also abolished the generation of ISC. When ISC were enumerated after a 7-day incubation with PWM, the addition of HU as late as day 6 of culture was found to inhibit responsiveness markedly. This suggested that those cells that had acquired the capacity to secrete lg were actively dividing, and continued division was necessary for ongoing lg secretion. To examine this possibility, experiments were carried out in which responsiveness was assayed on a daily basis. ISC could be detected after a 3- or 4-day incubation and reached maximum at day 6 or 7. Addition of HU on days 3 to 7 caused a highly significant reduction in the number of ISC within 24 hr. ISC did not begin to show resistance to the effects of HU until later in culture. This observation supported the conclusions that ISC were a rapidly cycling cell population and that ongoing lg secretion, as well as expansion in the number of ISC, depended on continued proliferation of the ISC. To confirm directly that ISC were a cycling cell population, PBM were cultured with PWM for 6 days, fixed, stained for both cytoplasmic lg and DNA content, and analyzed on the fluorescence-activated cell sorter. This method made it possible to quantitate the DNA content of individual lg-synthesizing cells and thus to determine their position in the cell cycle. As many as 40% of cytoplasmic lg-positive cells were found to be in the S, G2, or M phases of the cell cycle. These data indicate that ISC generated in man after in vitro stimulation with a number of polyclonal activators are not stable terminally differentiated lg-secreting plasma cells but rather an actively cycling lg-secreting population. Furthermore, the results indicate that proliferation of the ISC themselves plays an important role in determining the magnitude of the resultant antibody response.

Nonspecific reactions in the hemagglutination inhibition test for detection of rubella antibodies

Approximately 7% of the sera tested to determine the presence of rubella-specific antibodies by the hemagglutination inhibition test demonstrated abnormal patterns of reactivity, rendering the test unreadable. Another 3% of sera were shown to have false-positive titers as high as 1:128. When these abnormally reacting and false-positive sera were heated at 56 degrees C for 30 min after chemical treatment they always converted to negative, indicating the absence of specific rubella hemagglutination-inhibiting antibody. These results were confirmed by fractionation of the sera after sucrose gradient centrifugation. It was established that manifestation of these nonspecific results was dependent on the concentration of Ca2+ or Mn2+. The heat-labile inhibitor(s) responsible for abnormal and false-positive reactions was found not to be complement. This inhibitor(s) was detected in the light fractions of sera and when added to negative sera was capable of reproducing the abnormal patterns of reactivity. These results emphasize the necessity of heating sera for the rubella hemagglutination inhibition test after the chemical removal of nonspecific inhibitors.