Human B cell differentiation. II. Pokeweed mitogen-responsive B cells belong to a surface immunoglobulin D-negative subpopulation

Selective IgM deficiency in adults: phenotypically and functionally altered profiles of peripheral blood lymphocytes

Peripheral blood lymphocytes from four patients with selective IgM deficiency were examined phenotypically and functionally. Although B cell subpopulations determined by surface immunoglobulins were within normal or nearly normal range, T8+ cells were significantly increased and T4/T8 ratios were inverted in three patients. IgM specific hyporesponsiveness in the PWM-driven immunoglobulin production system was observed in all four patients. Ia-like antigen positive T cells were increased in two patients; both had increased Leu2a+ Leu15+ suppressor-effector cells. In addition, Leu3a+ Leu8+ suppressor-inducer cells were increased in one of these two patients. Excessive (either IgM-specific or isotype non-specific) suppressor activity of T cells and IgM specific hyporesponsiveness of non-T cells were observed in these two patients in the recombination plaque assay. Although these results showed the complexity of the pathogenesis of this syndrome, they suggested that suppressor-associated T cells may play a role in some patients with selective IgM deficiency.

IgG subclass potential of surface IgM-negative and surface IgM-positive human peripheral blood B cells

To examine the IgG subclass potential of B cells at various stages of maturation, human peripheral blood B cells were separated into surface IgM-positive (sIgM+) and surface IgM-negative (sIgM-) cells by panning techniques and cultured with pokeweed mitogen, LPS, or Epstein-Barr virus. At the end of 7 days, cells were harvested, counted, spun onto slides, fixed, and stained with subclass-specific monoclonal antibodies. In all experiments with all mitogens, there was an enrichment of IgG2 plasma cells in sIgM+ cultures compared to the sIgM- cultures (P less than 0.0001). In the Epstein-Barr virus-stimulated cultures there was also a statistically significant enrichment for IgG3 in the sIgM+ cultures (P less than 0.01). In contrast, sIgM- cultures were always enriched for IgG1 plasma cells (P less than 0.0001). In the pokeweed mitogen-stimulated cultures, the sIgM- cultures also contained a higher proportion of IgG4 plasma cells than did the sIgM+ cultures (P less than 0.01). These results demonstrate that the IgG subclass potential of immature, surface IgM-positive precursors of IgG plasma cells differs from that of more mature surface IgM-negative precursors.

IgG subclass distribution of serum antibodies against lipopolysaccharide from Bacteroides gingivalis in periodontal health and disease

Serum IgG1, IgG2, IgG3 and IgG4 antibody levels directed against lipopolysaccharide (LPS) from Bacteroides gingivalis were measured in the sera from systemically healthy subjects with and without periodontitis. An enzyme-linked immunosorbent assay was used that included coating of microtiter plates with LPS, and subsequent incubation with patient sera followed by mouse monoclonal subclass-specific antibodies, biotinylated sheep anti-mouse IgG and alkaline phosphatase conjugated to streptavidin. Anti-LPS IgG antibodies were dominated by IgG2, and moderate amounts only of IgG1, IgG3 and IgG4 were found. The periodontitis patients had significantly higher anti-LPS IgG1, IgG2 and IgG3 levels when compared to the subjects with healthy periodontium (p less than 0.05, Mann-Whitney test).

B lymphocyte activation by insoluble anti-mu antibodies in patients with systemic lupus erythematosus

In order to study the capacity of anti-immunoglobulin (Ig) antibodies to induce proliferative responses in peripheral blood mononuclear cells (PBC) from patients with systemic lupus erythematosus (SLE), anti-mu coupled to Sepharose beads (anti-mu) was used as a polyclonal activator. In 18 patients, a strong proliferative response was associated with inactive disease, and the response was lower in clinical active disease (P less than 0.02). An inverse correlation could also be observed in six patients who were studied longitudinally (P less than 0.01). These results indicate that anti-mu responsiveness is closely related to disease activity in SLE. In addition, sequential data obtained from two patients during an early stage of clinical deterioration suggest that a low anti-mu response might be an early indicator of a clinical relapse. In the patients investigated, the anti-mu response was not correlated with the response to pokeweed mitogen (PWM), or with the quantity of B cells. When T cell depleted cell fractions were studied, marked increases in the proliferative responses to anti-mu were observed in some patients. These studies suggest that the response to anti-mu might be modified by T cells to a variable extent in patients with SLE.

Functional heterogeneity of nonresting B cells in human blood

Among human peripheral blood B cells we localized the precursors of two interleukin-dependent B cell activation processes: the specific response to a particulate antigen, trinitrophenylated polyacrylamide beads (TNP-PAA) and the polyclonally induced response to pokeweed mitogen. In both cases the precursors belong to the OKB7+, sIgD-, mouse red blood cell- subpopulation. However, they differ when cell density, reflecting the stage of activation reached by B cells in peripheral blood, is considered. Only B cells of intermediate density respond to TNP-PAA, whereas the optimal response to pokeweed mitogen is obtained with the cells displaying the lower density. The lack of response of the more dense (resting) B cells to TNP-PAA suggests that the T dependency of this antigen is not based on linked recognition, and fits with our demonstration that this particulate antigen can trigger B cells in the presence of T cell factor. More importantly, our results show that nonresting B cells are functionally heterogeneous according to their degree of preactivation: the responsiveness to specific signals provided by a nonmitogenic hapten-carrier conjugate would be acquired before that to polyclonal activators.

Endothelial cell enhancement of PWM induced immunoglobulin synthesis by peripheral blood mononuclear cells

The effect of various exogenous cells on the in-vitro PWM stimulation of immunoglobulin synthesis by normal human peripheral blood mononuclear cells was investigated. The accessory cells tested were bovine and human endothelial cells, bovine and human fibroblasts, normal human monocytes, and a monocyte cell line U937. Bovine and human endothelial cells boosted PWM-induced IgG and IgM synthesis, sometimes threefold. The enhancement was maintained over the 7-11 day period of culture and probably required cell to cell contact. It was not seen with the other cell types added and was, therefore, unlikely to be a consequence of an allogeneic or a xenogeneic stimulation, or a nonspecific 'feeder cell' effect.

Ontogeny of B cells and pathogenesis of humoral immunodeficiencies

Studies of B-cell ontogeny have played an important role in furthering our understanding of the pathogenesis of immunodeficiencies. Development of clonal diversity for both T and B cells begins during the first trimester and is far advanced by midgestation. Fetal and neonatal B cells have a limited capacity to express IgG and IgA antibody responses, although precursors expressing these immunoglobulin classes are present. T-and B-cell interactions in the neonate are dominated by suppression. T helper cells are present and functional, but their capacity to drive IgG and IgA responses is impaired. This paper will review the major steps in ontogenetic development of B cells and the functions associated with each differentiation stage. Possible pathogenetic mechanisms of several humoral immunodeficiency diseases are reviewed from the perspective of the normal progression of B-cell differentiation.

Characteristics of human B cells responsive to the T-independent mitogen Branhamella catarrhalis

Non-T cells from tonsil or blood were fractionated according to buoyant density, isotype of surface immunoglobulin, or the ability to form rosettes with mouse erythrocytes. Each fraction was tested for the ability to proliferate in response to B. catarrhalis (Bc) and, for comparison, Staphylococcus aureus Cowan 1 (SAC) or an MLR supernatant (TF). Cells in all density fractions responded to Bc, the greatest response occurring in the high-density cell fraction. SAC could similarly induce proliferation in high-density cells, in contrast to TF which preferentially activated cells in the low-density fraction. When cells were fractionated by rosetting with mouse erythrocytes, both fractions (MRBC-R+ and MRBC-R-) responded to Bc and to SAC, whereas the greatest response to TF occurred in the MRBC-R- cell fraction. Depletion of sIgD+ sIgM+ cells almost completely abolished the response to Bc, suggesting that responsive cells express both these classes of immunoglobulin on their membrane. Furthermore inclusion of anti-delta antibodies in cultures resulted in failure to proliferate in response to Bc. These data strongly suggest that Bc, like SAC but in contrast to TF, is able to stimulate proliferation in cells with the characteristics of resting B cells, i.e., high-density, sIgD+ cells which form rosettes with MRBC. This may be related to the fact that Bc, like SAC, is able to bind to human immunoglobulins.

Human peripheral blood B cell subpopulations: surface IgD+ cells respond to pokeweed mitogen with plasma cell differentiation

Human peripheral blood (PB) mononuclear cells were depleted of T cells and subsequently of monocytes by counterflow centrifugation. The resulting B cell enriched fraction contained less than 3% T cells, 1 +/- 1% monocytes and 71 +/- 6% B cells. Approximately 56% of the B cells carried surface IgM (sIgM) and sIgD, the remaining 44% carried only one isotype (IgG, IgA, IgM or IgD). Using anti-delta or anti-mu-coated Ox red blood cells (OxRBC) the B cell enriched fraction was separated into a sIgD+ or sIgM+ and sIgD- or sIgM- fraction. The sIgD+ as well as the sIgM+ fraction responded (partially) to pokeweed mitogen (PWM) with plasma cell differentiation into cytoplasmic IgM (cIgM) containing cells. Cytoplasmic IgD+ cells were occasionally found in the sIgD+ or sIgM- fraction, but never in the sIgM+ fraction. Cells containing cIgG or cIgA were only found after stimulation of the sIgM- or sIgD- fraction, the latter also produced cIgM+ cells. In a second separation step of the sIgD- and sIgM- fraction with anti-alpha or anti-gamma-coated OxRBC it was shown that the cIgA+ and cIgG+ cells were derived from B cells expressing only sIgA or sIgG respectively. In conclusion, two major B cell subpopulations can be found in PB: a sIgM+D+ fraction, which gives rise to only cIgM+ plasma cells after PWM stimulation and a second population of B cells which express one heavy-chain isotype on their surface. These cells not only differentiate on PWM stimulation, but they also show a strong proliferative response.

Selective immunoglobulin M deficiency associated with disseminated molluscum contagiosum

A 16-year-old girl with disseminated molluscum contagiosum (MC) was found to have a very low level of serum IgM, elevated levels of IgG and IgA, and a high level of IgE. She had normal numbers of peripheral blood IgM+, IgG+ and IgA+ B-lymphocytes but their terminal differentiation into plasma cells could not be induced by pokeweed mitogen (PWM) in vitro. On the other hand, the patient's T-cells showed normal helper functions in the PWM system and normal interferon (IFN) production in vitro. However, the IgM+ B-cells can be induced to differentiate into IgM secreting cells by Epstein-Barr virus (EBV), suggesting that the genetic mechanism for synthesis of the component immunoglobulin proteins is present. T-cell functions were impaired, as shown by delayed type cutaneous hypersensitivity (DTH) and mitogen response. The data suggest that the selective IgM deficiency of the patient is due mainly to defects in B-cells at the terminal differentiation stage, but immunological abnormalities are present in both B and T-cell systems. Neutrophil functions examined were normal. MC was treated by intravenous injection of IFN without any side effects; however, no clinical improvement was achieved.

Induction of IgE synthesis in normal human B cells. Sequential requirements for activation by an alloreactive T cell clone and IgE-potentiating factors

Two human alloreactive T cell clones were established from a one-way mixed lymphocyte culture involving two nonatopic donors, and were assessed for their capacity to induce IgE synthesis by B cells obtained from the original stimulator. The two alloreactive T cell clones studied induced IgG but not IgE synthesis in normal B cells. However, one of the two clones, clone 2H6, induced IgE synthesis in the presence of supernatants from T cell lines derived from patients with the hyper-IgE syndrome (HIE), and enriched for T cells bearing receptors for IgE. These supernatants by themselves caused no IgE synthesis in nonatopic B cells. The potentiating factors in these supernatants were shown to bind to IgE. Time sequence experiments indicated that interaction of the B cells with the alloreactive clone 2H6 renders them responsive to the action of the IgE-potentiating factors. These results indicate that induction of IgE synthesis in normal B cells involves at least two sequential T cell derived signals. Furthermore, T cell clones are heterogenous in their capacity to provide these signals.

In vitro production of an anti-DNA idiotype by lymphocytes of normal subjects and patients with systemic lupus erythematosus

We investigated whether normal B cells can synthesize antibodies with an idiotypic marker that occurs with high frequency in anti-DNA antibodies of patients with systemic lupus erythematosus (SLE). This idiotype, Id16/6, has been found in the serum of patients with active SLE and in monoclonal anti-DNA antibodies derived from unrelated patients with the disease. We found that cultured lymphocytes of all normal subjects tested produced Id16/6 when stimulated by pokeweed mitogen (PWM). By contrast, lymphocytes from SLE patients produced Id16/6 even without mitogenic stimulation, whether or not they were obtained from patients in remission or relapse. Relapsed patients' lymphocytes spontaneously produced the highest levels of Id16/6 which was found in IgG and IgA, in addition to IgM. The majority of Id16/6 produced by PWM-stimulated lymphocytes from either normal subjects or patients in remission did not bind to nucleic acid. In relapse, however, the nucleic acid-binding proportion of Id16/6 rose substantially, indicating that the spontaneously activated B cells in active SLE differ from the subset of B cells that produce Id16/6 upon PWM stimulation. The findings suggest that the lupus Id16/6 family is conserved in normal individuals and it consists of two populations of antibodies with different antigenic specificities. The major set is not directed against nucleic acid antigens; its antigenic specificity is unknown and it dominates the Id16/6 family that appears after PWM stimulation. The other, minor set binds to nucleic acids and becomes prominent in clinically active lupus. These two sets of idiotypically related antibodies may be connected by an immunoregulatory network.

Abnormal B cell function in patients with Behçet's disease

We evaluated B lymphocyte function in 23 patients with Behçet's disease at various stages. The patients with active disease, but not those with inactive disease, were found to have elevated numbers of cells spontaneously secreting immunoglobulin and a decreased B cell response to the T cell-independent B cell mitogen, Staphylococcus aureus Cowan 1. Moreover, B cells from almost all patients with Behçet's disease were unresponsive to the T cell-dependent polyclonal activator, pokeweed mitogen. These results indicate that B cell abnormalities, including some which are associated with disease activity, could be involved in the pathogenesis of Behçet's disease.

Separation of human B lymphocytes on Helix pomatia A haemagglutinin into two major fractions differing in responsiveness to T-dependent mitogen (pokeweed mitogen) or antigen (tetanus toxoid)

A B-cell fraction consisting of 70% of cells carrying the B-cell-associated B1 antigen, 15-20% of M1+ non-B cells, and less than 3% of T cells was prepared from the peripheral blood of healthy human donors, previously vaccinated with tetanus toxoid (TT). As assessed by immunofluorescence after treatment with neuraminidase, approximately 40-50% of the B cells had surface structures binding to Helix pomatia A haemagglutinin (HP). The cells were separated into three fractions by affinity chromatography on HP conjugated to Sepharose (P, non-retained cells; EI, cells eluted with 0.1 mg/ml N-acetyl-D-galactosamine (D-GalNac); EII, cells eluted with 1 mg D-GalNac/ml). The majority of B cells in fraction EII were HP+ and were rich in cells expressing the B2 differentiation antigen. Sixty per cent of the B cells in this fraction also expressed the major HP-binding glycoprotein, gp 150. In the presence of autologous T cells, these B cells were strongly responsive to activation by either pokeweed mitogen (PWM) or antigen (TT), as reflected by differentiation into plasma cells, secretion of polyclonal IgG and IgM, or IgG anti-TT antibodies. In contrast, fraction P, which contained more than 90% HP-B cells, and which was partially depleted of B2+ cells, responded poorly or not at all to both PWM and TT. Fraction EI was a mixed fraction that responded in an intermediate fashion. When the preparations were depleted of contaminating non-B cells carrying the monocyte or large granular lymphocyte associated M1 antigen, their response to the two stimulating agents did not alter. The results suggest that HP+ B cells differ from HP-B cells in their responsiveness to T-cell signals. Fractionation on unsolubilized HP offers a simple and efficient way of separating B cells into at least two subsets differing in their responsiveness to T-cell-derived differentiation and maturation signals.

Surface phenotype and function of tonsillar germinal center and mantle zone B cell subsets

Human peripheral lymphoid tissues contain distinct B cell populations that differ in their buoyant density, cell surface phenotype, and responsiveness to proliferative signals. Two major B cells subpopulations from reactive tonsils or lymph nodes have phenotypes that appear to correspond to mantle zone and germinal center B cells. These subpopulations were distinguished using two-color immunofluorescence to measure surface IgM, IgD, DR, DQ, and Bp35 (B1) in pairwise combinations. The two populations were separated on density gradients, and their proliferative responses to activation signals was studied. The dense B cells proliferated in response to anti-mu on beads or anti-Bp35 antibodies but not to T cell-derived growth factors. The dense B cells are almost all IgM+IgD+Bp35dull (mantle zone phenotype). In contract, more buoyant B cells proliferated in response to T cell factors alone but not to anti-mu on beads or anti-Bp35. These cells are IgD-, express little or no IgM and higher levels of Bp35 (germinal center phenotype). An additional minor subpopulation of dense Bp35dull IgD- B cells was detected in tonsils, suggesting that IgD may be lost prior to B cell entry into germinal centers. B cells in peripheral blood and spleen have surface phenotypes distinct from each other and from the tonsil subpopulations. In particular, the levels of IgM, Bp35, and DR all vary among different lymphoid locations. The mean surface density of DR is low in peripheral blood, intermediate in the spleen, and highest in reactive tonsils and lymph nodes. While Bp35 surface level does correlate with the stage of B cell activation, the surface level of DR, DQ, or DP does not since the surface density of DR, DQ, and DP are similar on both mantle zone and germinal center B cells. Both tonsillar populations express a wide range of class II antigen densities and display coordinate expression of DR and DQ antigen levels.

Pokeweed mitogen and Staphylococcus aureus Cowan I induced immunoglobulin A synthesis by lymphocytes of IgA deficient blood donors

In vitro IgA synthesis induced by pokeweed mitogen (PWM), Staphylococcus aureus Cowan I (STA), and combinations of STA and PWM (STA/PWM) was studied in lymphocytes of IgA deficient (sIgAd) blood donors. Cultures of T-depleted (non-T) cells with autologous or allogeneic control T, irradiated T (T), or T4 cells suggested abnormalities in non-T cell fractions in most (12/22) sIgAd donors. T cell abnormalities in themselves, detectable in six donors, did not appear to account for the failure of IgA synthesis. Repeat studies in 10 donors indicated fluctuations in in vitro IgA synthesis in four. IgA synthesis induced by STA/PWM combinations was observed in only one of eight sIgAd donors. Our findings suggest that in some donors defects leading to failure to produce IgA may not be constant and support the hypothesis of a maturation arrest in IgA+ B cells in sIgAd donors.

Induction of sIg-negative B lymphocytes for differentiation by PWM

It has been reported in the literature that PWM-responsive B lymphocytes are sIgM+, sIgD-, lack receptors for mouse erythrocytes, and are larger than PWM-negative lymphocytes. This paper describes the observation of B cells among the thymocytes from a patient with myasthenia gravis. In the thymocytes, actually no sIg+ cell was found, and Staphylococcus aureus Cowen strain I could not induce the mononuclear cells in the thymus to differentiate. It was surprising that 6.9 per cent of the cells were BA-1 positive cells. At the same time, in the presence of PWM, 9680 +/- 555 cells out of 1 X 10(-6) thymocytes could be induced to differentiate to immunoglobulin-secreting cells (ISC) in culture. This result suggests that PWM might be able to induce sIg- B lymphocytes to differentiate as well.

Enhancement of the impaired autologous mixed leukocyte reaction in patients with systemic lupus erythematosus

The cellular basis of the impaired autologous mixed leukocyte reaction (AMLR) in patients with systemic lupus erythematosus (SLE) was investigated. Non-T cells from normal subjects and from SLE patients were fractionated into low and high density subpopulations. SLE patients were found to have an increased proportion of low density to high density non-T cells when compared to normal subjects. Although normal low-density non-T cells were highly enriched in AMLR stimulatory capacity, SLE low-density non-T cells induced minimal proliferation by autologous T cells. Brief incubation of SLE non-T cells with phorbol myristate acetate or formalin-treated Staphylococcus aureus resulted in marked augmentation of the capacity of those non-T cells to stimulate an AMLR, although the magnitude of the activated non-T cell-induced AMLR did not achieve that observed in normal subjects. No significant alterations in the expression of Ia molecules on the surface of the non-T cells were detected after in vitro activation. These experiments support the hypothesis that the impaired capacity of SLE T lymphocytes to proliferate in response to autologous non-T cells may in part represent a failure of SLE non-T cells to present an appropriate stimulus for the generation of a T cell response.

In vitro studies on the mechanism of increased serum IgM levels in primary biliary cirrhosis

To evaluate the mechanisms underlying the increase in serum IgM in primary biliary cirrhosis (PBC) studies were designed to examine IgM production in vitro and to assess the relative contribution of intrinsic B cell activity and immunoregulatory T cell balance to IgM synthesis. The number of peripheral blood lymphocytes (PBL) producing IgM (spontaneous and pokeweed mitogen (PWM) stimulated) at the end of a seven day culture period was similar in PBC patients and control subjects while the amount of IgM synthesized (spontaneous and PWM stimulated) during this period was significantly greater in the patient group, implying that the amount of IgM produced per B cell was increased in PBC. Co-culture of autologous and allogeneic T and B lymphocytes and irradiation of T lymphocytes from patients and normal subjects clearly implicated abnormal suppressor T cell function, rather than autonomous B cell hyperactivity, as the cause of the increased IgM synthesis. Direct studies of T cell function indicated that although concanavalin A (Con A) activated suppressor cells inhibited proliferation of IgM producing B cells in the majority of PBC patients, they were unable to inhibit IgM synthesis. The demonstration of a disparity between IgM synthesis and the proliferation of IgM-producing B cells, together with the observation that the abnormality of T cell function is largely confined to the control of IgM secretion, is consistent with the presence of at least two different suppressor subpopulations regulating IgM production. In PBC the main suppressor cell abnormality seems to affect regulation of IgM secretion rather than B cell proliferation.

Development of B lymphocyte function in childhood

The capacity of blood lymphocytes of children aged from birth to six years to produce immunoglobulins was studied in vitro at the cell level using a direct B lymphocyte activator (Epstein-Barr virus) or a T lymphocyte dependent B lymphocyte activator (pokeweed mitogen). Umbilical cord blood lymphocytes secreted IgM at adult levels after Epstein-Barr virus stimulation, while the ability to synthesize IgG and IgA increased up to the ages of 1 and 2 years, respectively, but not beyond this period. IgG3 production preceded that of the other IgG subclasses. The T lymphocyte dependent IgM synthesis was low at birth, but approached adult levels at two years of age. T cell dependent IgG and IgA secretion, however, remained reduced even up to 6 years of age.

B-CLL cell surface markers and mitogen-induced thymidine uptake: a comparison between lymph node cells and peripheral blood lymphocytes in 25 patients

Lymphocytes from peripheral blood and lymph nodes from 25 patients with B-CLL were analysed by immunofluorescent staining of surface membrane immunoglobulin (SmIg), the B-cell marker B1, and the T-cell markers Leu 1/2/3/4. Tritium-thymidine uptake was measured in mitogen-stimulated 4-day cultures. Differences in these parameters between cells from the two sources in each patient were calculated with the paired T-test. All cell samples showed a clonal B-cell population. More blood lymphocytes than lymph node cells expressed the monoclonal SmIg (mu or gamma, p = 0.04; kappa or lambda, p less than 0.01), and T-cells were more frequent in lymph nodes (p = 0.01), where the T helper/suppressor ratio was higher. Furthermore, lymph node cells showed a higher thymidine uptake in response to the mitogens LPS, PWM, and Cowan (p = 0.01, p = 0.01, and p = 0.004, respectively), but there was no difference in the responses to EBV, DxS, TPA and PHA (p greater than 0.5). The higher response in lymph node cells to some mitogens might in part be explained by differences in the numbers of accessory cells, such as T-helper cells, but also by the existence of leukaemic B-cell subsets with different mitogen response patterns and different distributions within the lymphoid compartments. The characterization of subsets within a malignant cell clone might be of clinical importance.

In vitro T-cell dependent B-cell activity in myasthenia gravis

The in vitro T-cell dependent B-cell activity was analysed in 34 patients with myasthenia gravis and in 16 controls by culturing 1 X 10(6) peripheral blood lymphocytes for 8 days with or without pokeweed mitogen (PWM) and measuring the amounts of IgG and IgM released into the culture supernatant. Increased production of IgG in the unstimulated cultures was found in 20 patients, 8 of whom also produced increased amounts of IgM. Upon PWM stimulation the patients produced normal amounts of IgG. The IgM production, however, was decreased in the patient population compared to the controls. Only one of the controls produced more IgG than IgM, either unstimulated or during PWM stimulation. In contrast 10 patients produced more IgG than IgM in the unstimulated cultures and 15 patients did so during PWM stimulation. The 'spontaneous' production of immunoglobulins was not measurable before 4 days of culture and was not the result of in vivo activated B-cells. We suggest that the increased 'spontaneous' immunoglobulin production and the decreased production of IgM during PWM stimulation may be a result of abnormal T-cell activity. The abnormalities found were not related to disease activity, the presence of multiple autoantibodies in the serum, steroid therapy or previous thymectomy. Besides these abnormalities, patients not treated with immunosuppressive drugs also showed decreased PWM induced IgG synthesis.

Differential requirements of B cells from normal and allergic subjects for the induction of IgE synthesis by an alloreactive T cell clone

Human T cell helper/inducer clones were used to induce IgE synthesis in B cells from both allergic and nonallergic donors. An alloreactive T cell clone, activated by recognition of specific HLA-DR antigens, stimulated peripheral blood B cells from both allergic and nonallergic donors to synthesize IgE antibody. B cells of allergic donors differed from those of nonallergic donors in their requirements for induction of IgE synthesis. Induction of IgE synthesis in B cells from nonallergic individuals occurred only under conditions of cognate interaction, in which the B cells expressed the alloantigen recognized by the T cells. In contrast, IgE synthesis in B cells from allergic donors occurred under conditions of cognate interaction with T cells as well as bystander conditions where the B cells did not express the alloantigen recognized by the T cell clones and where the T cell clones were stimulated by third-party monocytes bearing the relevant alloantigens. Furthermore, bystander stimulation of IgE synthesis in allergic donors occurred in the presence of tetanus toxoid (TT) antigen-specific T cell clones activated by the appropriate TT-pulsed monocytes. In contrast to the differing requirements of B cells from normal vs. allergic subjects for the induction of IgE synthesis, these B cells did not differ in their requirements for the induction of IgG synthesis. IgG synthesis was induced in all B cells under conditions of cognate interaction with the T cells as well as under conditions of bystander stimulation. These results suggest that cognate T-B cell interactions may be important in the development of IgE immune responses in the normal host.

Defective in vitro antibody production in response to pokeweed mitogen and influenza antigen in patients with Hodgkin's disease

Cultures of peripheral blood mononuclear cells (PBM) from 33 patients with Hodgkin's disease, were stimulated in vitro with pokeweed mitogen (PWM) or influenza antigen. Impaired production of immunoglobulin (Ig) of one or more of the three main classes (IgG, IgM and IgA) in PWM stimulated cultures was found in 22 patients and in 11 patients no Ig of any class was produced. Antibody to influenza virus was detected in PWM stimulated PBM cultures in 13 of 14 normal individuals, but in only four of 25 patients with treated Hodgkin's disease though IgG was produced in 16 of 25. Influenza antigen induced anti-influenza antibody production in 10 of 12 cultures from normal individuals but in only two of 22 from patients. The results confirm our earlier report of defective antibody production in vitro by PBM from patients with Hodgkin's disease and indicate that polyclonally activated production of immunoglobulins of several classes is defective, though in vivo humoral immunity is normal.

Abnormalities of B-cell activation and immunoregulation in splenectomized patients

Using a reverse hemolytic plaque assay as the effector system, we studied B-lymphocyte function in 12 patients after posttraumatic splenectomy, as well as in 25 normal individuals. The time interval between the splenectomy and the immunological studies varied between 2 days and 7 years. Compared to normal individuals, the splenectomized patients had markedly elevated numbers of spontaneous immunoglobulin-secreting cells (ISC) and severely decreased responses to the polyclonal activator pokeweed mitogen. A tendency towards normalization of these abnormalities, especially the high spontaneous ISC levels, could be observed during the time interval extending up to 7 years after splenectomy. In order to characterize the mechanism responsible for the altered immune response in splenectomized patients, co-culture experiments with unseparated and separated lymphocytes were performed. These revealed an impaired T-helper cell capacity as well as an intrinsic B-cell defect. Marker analyses with monoclonal antibodies revealed normal proportions with the exception of OKT 4 positive and B 1 positive cells that identify T-helper/inducer and peripheral B-cells respectively. We conclude that immune dysfunction in peripheral blood lymphocytes of splenectomized patients involves mainly the B-cell as well as the T-helper/inducer-cell population.

Effects of in vitro corticosteroids on B cell activation, proliferation, and differentiation

The present study demonstrates the graded effect of in vitro corticosteroids (CSs) on the different phases of B cell activation, proliferation, and differentiation. Early events such as activation and proliferation of high-dose anti-mu or Staphylococcus aureus-stimulated B cells are profoundly suppressed by the presence of in vitro CSs. The suppressed proliferative response may be mediated by a direct effect on B cells and/or modulation of accessory cell function. Later events in the B cell cycle such as the proliferative response to B cell growth factor after either in vivo or in vitro activation are less sensitive to the suppressive effects of in vitro CSs. The final events in the B cell cycle; namely, the differentiation to the immunoglobulin-producing state, is not suppressed by in vitro CSs. Indeed, depending on the systems employed, there is either no effect or enhancement of immunoglobulin secretion by the presence of in vitro CSs. The graded effect of in vitro CSs on the discrete phases of the B cell activation, proliferation, and differentiation cycle provide new insights into the complex nature of CS-induced modulation of human B cell responses.

Immunoglobulin M and immunoglobulin G secretion by human B cells exposed to RU 41.740, a glycoprotein extract from Klebsiella pneumoniae

RU 41.740, a glycoprotein extract from Klebsiella pneumoniae, was seen to activate human B cells to immunoglobulin secretion in vitro. The effects of RU 41.740 on human B cells were compared to those induced by pokeweed mitogen, a T-cell-dependent polyclonal B-cell activator, and Epstein-Barr virus, a T-cell-independent polyclonal B-cell activator. Exposure of human B cells to all of these agents resulted in increased immunoglobulin M (IgM) and immunoglobulin G (IgG) secretion. IgM and IgG secretion induced by RU 41.740 appeared to be T cell dependent when B cells were isolated from human peripheral blood. However, this activity may have been T cell independent when B cells were isolated from human spleen. RU 41.740-induced IgM secretion by peripheral blood B cells was seen to peak after 6 days in culture; IgG secretion peaked after 7 days in culture. The optimal concentration of RU 41.740 for the induction of IgM and IgG secretion by human B cells in vitro was seen to be 200 micrograms/ml.

Activated B lymphocytes: stimulators of an augmented autologous mixed leukocyte reaction

The characteristics of the non-T cell(s) which stimulate T-lymphocyte proliferation in the autologous mixed leukocyte reaction (AMLR) have been at issue since this in vitro reaction was first described. Dendritic cells have been shown to be the most potent stimulator cells, but B cells, null cells, and macrophages have also been demonstrated to have the capacity to stimulate autologous T-cell proliferation. A cell preparation obtained from human peripheral blood was highly enriched for surface immunoglobulin-positive B cells. These cells were activated by brief culture with various B-cell mitogens and then compared to untreated B cells with regard to stimulatory activity in the AMLR. Mitogen-activated B cells were markedly augmented in their capacity to stimulate autologous T-cell proliferation when compared with untreated B cells. Fractionation of the B-cell preparation into high- and low-density subpopulations demonstrated that the high-density cells, enriched in resting B cells, had minimal stimulatory activity but could be activated to have increased AMLR-stimulatory capacity. Proliferation of the activated B lymphocytes was not required for the generation of the augmented AMLR. Response to both untreated and mitogen-activated B cells was a property of T4-positive T lymphocytes. The increase in stimulatory capacity was associated with a decrease in cell surface immunoglobulin, but no significant alteration in the percentage or fluorescence intensity of anti-Ia staining cells was detected. Activated B cells which are generated in vivo may acquire the capacity to generate T effector cells or factors important in the regulation of B-cell function.

Interleukin 2 receptors on human B cells. Implications for the role of interleukin 2 in human B cell function

In the present study, we examined the expression of interleukin 2 (IL-2) receptors on normal human B cells as well as established B cell lines. Anti-Tac monoclonal antibody did not bind to freshly separated normal human B cells. Unexpectedly, with the appropriate activation of the normal B cells by anti-mu antibody, phorbol myristate acetate, or Staphylococcus aureus Cowan I (SAC), Tac antigen was induced on the activated B cells. Anti-Tac antibody showed consistent reactivity with two B cell lines that were infected by human T cell leukemia virus (HTLV) and some reactivity with two out of eight Epstein-Barr virus-transformed B cell lines established from normal adult donors. Immunoprecipitation analysis revealed that antigens of similar size with a molecular weight of 50,000-60,000 can be precipitated with anti-Tac antibody from phytohemagglutinin-stimulated normal T cell blasts and normal activated B cells, as well as a cloned B cell line. Binding assays of IL-2 on normal activated B cells and on the cloned B cell (HS1) revealed that B cells have significantly fewer sites and lower-affinity IL-2 receptors compared with phytohemagglutinin-stimulated normal T cell blasts. Finally, biological properties of the IL-2 receptor on B cells were examined by incubating B cells with recombinant IL-2. It was found that moderate concentrations of IL-2 induce significant enhancement of proliferation and differentiation in SAC-activated normal B cells. These results suggest that normal B cells may express functional IL-2 receptors or closely related proteins and thus IL-2 may play a significant role in the modulation of B cell function.

Human blood B lymphocytes with receptors for sheep erythrocytes--their relevance in techniques to obtain T cells depleted of mature B cells

After B lymphocyte depletion, blood lymphocytes (PBMC) from certain individuals will generate substantial quantities of immunoglobulin (Ig) when cultured with pokeweed mitogen (PWM). The present investigations were aimed at analysing the cell subset in these T cell preparations, that was responsible for Ig production especially since the quantity of Ig generated was disproportionate to numbers of contaminating sIg-bearing B cells. Ficoll-Hypaque PBMC from 17 individuals were subjected to overnight sheep erythrocyte rosetting. Rosetted cells were subjected to very slow (100 X g) density gradient centrifugation to isolate T rosettes (and deplete PBMC of B cells). In 6 of these 17 individuals, such enriched T cells repeatedly generated substantial quantities of plasmacytoid cells after an 8-day culture in the presence of PWM and helper factors. Mean values for plasmacytoid cells per 1000 cells recovered were as follows: T cells 168.16 +/- 96.7 SD, B cells 226.67 +/- 161.1, PBMC 225.67 +/- 78.9. In further experiments, contaminating surface immunoglobulin (sIg)-positive B cells (less than 2% sIg-positive) were removed from the T cell preparations by the "panning" method, i.e. layering T cells on plates precoated with antisera specific for human Ig (polyvalent), and lysis of B cells with a monoclonal antibody BA-1. In these 6 individuals, removal of B cells by both these techniques completely abolished generation of plasmacytoid cells, thus confirming that it is a contaminating B cell subset which is responsible for Ig production in these T cell preparations. These data indicate that in certain individuals there are B cells that separate out with T cells during the E-rosette isolation procedure. With double immunofluorescence techniques, it became apparent that 4.8 +/- 1.3% of TRITC-labeled sIgM-bearing B cells were also labeled with FITC-conjugated monoclonal antibody to the sheep erythrocyte receptor. Kuritani and Cooper have previously demonstrated that PWM-responsive B cell precursors of IgM, IgG, or IgA plasmacytoid cells lack sIgD and, hence, comprise about 10-15% of the total B cells in PBMC. Our data would indicate that in certain individuals, about half this subset forms E-rosettes, which may explain why both E-rosette separated T cells and enriched B cells make similar quantities of plasmacytoid cells.

Production of IgE-potentiating factor in man by T cell lines bearing Fc receptors for IgE

The regulation of human IgE production in vitro by soluble T cell factors was examined. T cells were isolated from the peripheral blood of 2 patients with the hyper-IgE syndrome on the basis of their expression of Fc receptors for human IgE (Fc epsilon R). The T cells were incubated with human myeloma IgE (10 micrograms/ml), washed, reacted with immunosorbent-purified goat anti-human IgE conjugated with fluorescein isothiocyanate, and then separated into Fc epsilon R+ and Fc epsilon R- T cells on the fluorescence-activated cell sorter. Fc epsilon R+ T cells and Fc epsilon R- T cells were propagated in culture using supernatants of phytohemagglutinin-stimulated peripheral blood mononuclear cells (PBMC) and irradiated autologous PBMC. Supernatants of Fc epsilon R+ T cell lines but not of Fc epsilon R- T cell lines selectively enhanced IgE synthesis in cultures of B cells obtained from patients with allergic rhinitis but not from normal nonallergic subjects. The surface phenotype of the Fc epsilon R+ T cell line was predominantly T3+, T4+, Ia+ with few (15%) T8+ cells. Two T cell clones were grown from the Fc epsilon R+ T cell line by limiting dilution (0.3 cells/well). These clones possessed the T4+ helper/inducer phenotype and secreted IgE-enhancing factor(s). The IgE-enhancing factor(s) which had affinity for insolubilized human IgE was sensitive to treatment with trypsin and neuraminidase, and had as its target an IgE-bearing B cell. These results suggest that a subset of human T cells bearing an Fc epsilon R secretes an IgE-binding glycoprotein which selectively enhances IgE synthesis by IgE-bearing B cells.

Discontinuous expression of a membrane antigen (HB-7) during B lymphocyte differentiation

We have examined the expression of a cell surface antigen by B lineage cells in human fetuses, newborns and adults using a newly produced monoclonal antibody, HB-7. The HB-7 antigen was found to be a protease sensitive 45,000 MW molecule that appeared to be the same molecule recognized by the OKT-10 antibody. The HB-7 reactive molecule was expressed by all fetal pre-B and B cells, and 50% of newborn blood and adult bone marrow B cells. In contrast, only a small minority of B cells (2-12%) from blood, spleen and tonsil of adults were weakly HB-7+. The pokeweed mitogen-responsive B cell precursors of plasma cells were also HB-7-, but the HB-7 antigen was re-expressed during the plasma cell stage. We conclude that this antigen is unique among known B cell differentiation antigens in its intermittent pattern of expression during B cell development. The reactivity of the HB-7 antibody with immature, but not mature, B cells makes it well suited for studies of B cell ontogeny.

T-cell regulation of IgG subclass expression by mitogen-induced plasma cells: soluble factors versus the T cells

The human IgG subclasses expressed by plasma cells generated from circulating B cells in response to soluble T-cell factors were examined by immunofluorescence using subclass-specific monoclonal antibodies. Soluble T-cell factors were induced by a mixed lymphocyte reaction, pokeweed mitogen (PWM), or phytohemagglutinin. The distribution of IgG subclasses expressed by plasma cells induced by these factors was IgG2 greater than 75%, IgG1 less than 25%, IgG3 less than 1%, and IgG4 less than 1%. On the other hand, IgG1 was dominant when B cells were cultured with T cells and PWM: IgG1 approximately 70%, IgG2 approximately 20%, IgG3 approximately 8%, and IgG4 approximately 1%. The addition of different amounts of the T-cell factors to B cells in culture did not alter the predominance of IgG2 plasma-cell differentiation. These results suggest that T cells and their soluble factors may preferentially enhance terminal differentiation of different IgG B-cell subpopulations. In contrast, the ratio of IgA1 to IgA2 plasma-cell responses was approximately 1.5 to 1 regardless of whether the B-cell precursors were induced by T-cell factors or by the T cells plus PWM.

Induction of maturation of human B-cell lymphomas in vitro. Morphologic changes in relation to immunoglobulin and DNA synthesis

In vitro stimulation of cells from 8 non-Hodgkin's lymphomas comprising several histologic types with a tumor promotor (TPA) and with or without anti-immunoglobulins directed against the surface immunoglobulin of the tumor cells is reported. Morphologic transformation to immunoblastic and plasmablastic cells, but not to plasma cells, and induction of Ig and DNA synthesis were observed. A comparative analysis, including flow cytofluorometry, light microscopy combined with immunocytochemistry, and electron microscopy, suggests that the three events may not always be associated phenomena at the single-cell level even in monoclonal cell populations.

Human tonsil B lymphocyte function. I. The proliferative response to Staphylococcus aureus and pokeweed mitogen in relation to surface heavy chains mu and delta

Human tonsil non-T cells were separated into surface IgD positive (sIgD+), surface IgD negative (sIgD-), sIgM+ and sIgM- fractions by rosetting and gradient centrifugation with ox red blood cells, coated with immunosorbent purified goat anti-human heavy chain antibodies. No activation or suppression was found as a result of the separation technique. The sIg patterns of the isolated B cell fractions showed the effectiveness of the separations; sIgD+ and sIgM+ fractions were to a great extent overlapping populations, but there was a definite population of s mu + delta- cells (about 20% of the sIgD- fraction). The isolated fractions were tested for proliferative responses to Staphylococcus aureus (Sta) and pokeweed mitogen (PWM). The sIgM+ fraction showed the best response to Sta, eight times better than the sIgM- fraction, while the sIgD+ and sIgD- fraction showed equal responses to Sta. The sIgM- fraction responded best to PWM but all fractions responded quite well. Our results indicate that PWM is a mitogen to a whole variety of rather mature B cells while the Sta target B cell is restricted to the relatively immature sIgM+D- and sIgM+D+ cells.

Mitogenic stimulation of malignant B cells. Chronic lymphocytic leukaemia: secretion of monoclonal IgM by in vitro-induced plasmablasts

This study provides evidence that leukaemic B cells are able to proliferate and differentiate into plasmablasts. The Ig produced was monoclonal in nature and this was shown by gel electrophoresis.

Evidence for B cell activation in patients with active rheumatoid arthritis

Peripheral blood lymphocytes and in some cases synovial eluate cells from 51 patients with rheumatoid arthritis (RA), were analysed for the percentages of cells bearing surface light chains (total B cells), IgM and IgD. In addition, their capacity to form rosettes with mouse erythrocytes (mRFC)--a property of a B cell subpopulation--was determined. Activity of the disease was assessed by clinical and laboratory criteria and classified as very active, moderately active and inactive. Normal, age and sex matched individuals and a group of patients with a variety of other rheumatological disorders, were used as control populations. Although there was no significant difference in percentages of total B cells in any of the groups compared with normal controls, there was a small but significant increase in the ratio of cells bearing IgM to those bearing IgD in patients with very active disease. This was paralleled by a significant decrease in the mRFC in this disease activity group. Patients with inactive disease showed no change in their proportions of IgM:IgD, but did show a significant increase in mRFC. These results are discussed in terms of the presence of activated B cells in patients with very active RA.

Dissociation of stimulatory capacity in mixed lymphocyte reaction and proliferative responses to pokeweed mitogen among peripheral blood non-T cells

The stimulatory capacity in mixed lymphocyte reaction (MLR) and responsiveness to pokeweed mitogen (PWM) by peripheral blood non-T cells were studied. E rosette- and adherent cell-depleted lymphocytes were divided into low, medium and high density populations using discontinuous Percoll gradient. Low density non-T cells were potent stimulators in both autologous and allogeneic MLR despite low proliferative response to PWM. In contrast, those with medium density showed weaker stimulation in autologous though not in allogeneic reactions and underwent strong blastogenesis in PWM cultures. Non-T cells with high density had low MLR-stimulatory capacity and yet manifested the highest stimulation indices on PWM stimulation. These findings suggest that functional characteristics of non-T cells may be separable on the basis of cell density.

A cloned major histocompatibility complex-restricted trinitrophenyl-reactive human helper T cell line that activates B cell subsets via two distinct pathways

A cloned, trinitrophenyl (TNP)-specific helper T cell line (TCL), termed E-11, has been established in long-term, interleukin 2-dependent culture and used to study human T helper (Th)-B cell collaboration. Co-culture of E-11 with TNP-modified, but not unmodified or FITC-modified, autologous B cells results in a vigorous, polyclonally plaque-forming cell (PFC) response. E-11 helper activity is not constitutive, but requires antigen-specific, major histocompatibility complex-restricted activation of the TCL cells by interaction with TNP-modified autologous or DR 5+ allogeneic macrophages. Using B cell subsets isolated by discontinuous density gradient cengrifugation as responder populations, we determined that E-11 activates B cell subsets via two distinct mechanisms: (a) E-11 polyclonally activates large B cells in an unrestricted and nonspecific manner; and (b) E-11 preferentially induces a PFC response by TNP-modified small B cells. These results suggest that the large B cell subset is activated by helper signals generated during the Th-antigen-presenting cell interaction, while small B cells require an additional stimulus that is provided by antigen-specific Th-B cell contact.

Immunoregulatory T cell subpopulations in man: dissection by monoclonal antibodies and Fc-receptors

Until now, most of the studies on regulatory T cells have been based on culture systems in which human peripheral blood cells are stimulated by polyclonal stimulators like Pokeweed Mitogen (PWM). Our present contribution, however, deals with T cell-mediated regulation of the antigen-induced B cell activation, which exclusively leads to an antigen-specific IgM production (Heijnen et al. 1979a). Some authors' reports on regulatory activities of T cells, as tested in systems using polyclonal stimulators, differ from ours. This may be due to: a) as a result of polyclonal stimulus, various types of regulatory T cells are activated at the same time b) in contrast to a primary antigen, a polyclonal stimulator induces a rapid proliferation of the various regulatory T cells c) a polyclonal stimulator induces the differentiation of B cells in various maturational stages, that might each require additional or different regulatory signals. For example, Thomas et al. (1981) have shown that freshly isolated T4+ cells can induce suppressor activity in unprimed T8+ cells in the presence of PWM, whereas T4+ cells, precultured for 24 h in the presence of PWM, can exert a suppressor activity themselves without an apparent need for T8+ cells. In the antigen-specific system, however, we have neither been able to detect T suppressor effector activity in a population of primed T4+ cells, nor been able to demonstrate T suppressor inducer activity in unprimed T4+ cells (Heijnen et al. 1982a). Therefore the state of activation of the total T4+ population will dictate the balance of the total T helper and T suppressor activity. As a result of proliferation induced by polyclonal mitogens, small subsets of regulatory T cells, which are functionally undetectable in the primary antigen-specific assay, can expand sufficiently to have a measurable effect. Thomas et al. (1980) have shown that the T4+ suppressor inducer cell in the PWM system is radio-sensitive, which is in contrast with our data in the antigen-specific system. This may imply that we are looking at different subsets of T suppressor inducer cells in these different systems, but it might also indicate that T suppressor inducer cells need to proliferate in order to be able to measurably regulate the large pool of responding cells generated in the PWM system. Apart from such quantitative effects, polyclonal B cell activators like PWM are capable of inducing the differentiation of B cells in various maturational stages (Kuritani & Cooper 1982, Stevens 1982, Peters & Fauci 1983). Since it is highly likely that the regulation of these various B cell subsets might require different regulatory signals, the PWM model might be a very complicated model to study regulatory effects of single T cell subsets.(ABSTRACT TRUNCATED AT 400 WORDS)

Abnormalities of B-cell activation and immunoregulation in patients with the acquired immunodeficiency syndrome

We studied B-lymphocyte function in 12 homosexual male patients with the acquired immunodeficiency syndrome, 5 healthy homosexual men, and 12 heterosexual controls. In comparison with the heterosexual controls, the patients were found to have elevated numbers of cells spontaneously secreting immunoglobulin, decreased B-cell proliferative responses to T-cell-independent B-cell mitogens, and qualitatively deficient helper T cells. The hyperactive spontaneous B-cell responses as well as the refractoriness to signals for T-cell-independent B-cell activation were highly suggestive of an in vivo polyclonal activation of B cells and may have been responsible for the manifestations of B-cell hyperreactivity, such as hypergammaglobulinemia, seen in these patients. We conclude that the scope of immune dysfunction in the acquired immunodeficiency syndrome involves B cells as well as T cells.

Epstein-Barr virus-induced immunoglobulin synthesis by B cells from individuals with late-onset panhypogammaglobulinemia

Epstein-Barr virus (EBV) transformation was used to examine the differentiation potential of circulating B cells from eight individuals with late-onset panhypogammaglobulinemia. Cytoplasmic and secreted immunoglobulins were evaluated by immunofluorescence and radioimmunoassay. EBV-infected cultures of B cells from patients and healthy controls generated similar numbers of IgM-secreting plasma cells, but relatively few IgG and IgA plasma cells were induced in cultures of patients' B cells. As further evidence of B-cell immaturity, approximately 90% of the IgA B cells in the eight patients coexpressed IgM. Clonal diversity of B cells from hypogammaglobulinemic patients was examined with a panel of mouse monoclonal antibodies directed against idiotypic and VH subgroup determinants. The frequencies of EBV-induced plasma cells exhibiting the different idiotypic and VH determinants were similar for patients and controls. The data suggest the continued generation of clonally diverse B cells that are capable of terminal plasma-cell differentiation when the normal triggering mechanisms are bypassed by EBV. The arrested differentiation at an immature B-cell stage in these hypogammaglobulinemic individuals would appear to reflect a defect in normal B-cell triggering.

Specific in vitro antimannan-rich antigen of Candida albicans antibody production by sensitized human blood lymphocytes

We have developed a new antigenic system for the induction of specific in vitro antibody response in man. The antigen used was purified from the cell wall of Candida albicans strain A and contained greater than 96% polysaccharide mannan. Peripheral blood mononuclear cells from Candida-sensitized donors produced specific antimannan antibodies during a 7-d culture in the presence of mannan absorbed with methylated bovine serum albumin. Two methods were used to detect antimannan antibody responses. Antimannan antibody-producing cells were identified by radioautography with tritiated mannan. Antibody concentration in culture supernatants was measured by an enzyme-linked immunosorbent assay. In both methods, specific IgM and IgG (but not IgA) antibodies were detected. The antibody production to mannan was specific, since an antigenically unrelated polysaccharide (pneumococcal antigen S III) did not bind to methylated bovine serum albumin-mannan-induced blast cells and did not induce antimannan antibody-containing cells. Furthermore, a pulse with an excess of unlabeled mannan abolished [3H]mannan binding, whereas an excess of unlabeled S III did not. Similarly, no antimannan antibody was obtained in influenza virus-stimulated cultures and mannan-stimulated cultures were not inducing antiinfluenza antibodies. The antimannan antibody production was shown to be a T cell-dependent phenomenon. The T helper effect appeared to be radiosensitive. It was under a genetic restriction as it occurred only in autologous or semi-identical but not in allogeneic situations. This system is relatively simple, reproducible, and well suited for the study of specific secondary in vitro antibody responses to polysaccharide antigens in humans.

Frequencies of the separate human B cell subsets activatable to Ig secretion by Epstein-Barr virus and pokeweed mitogen

We have developed a microculture system suitable for limiting dilution analysis of Epstein-Barr virus (EBV)- and pokeweed mitogen (PWM)-induced activation of immunoglobulin secretion by human B cells. It was found that exogenous filler cells were not required to obtain optimal EBV-induced B cell precursor frequency (PF) estimates, although filler T cells were required for optimal PWM activation. In fact, when autologous T cells were used as filler cells, a marked decrease in the EBV-induced IgM PF was noted. Treatment of the T cells with cyclosporin A partially eliminated, and irradiation of the T cells completely eliminated, this decrease. The calculated PF of B cells activated by EBV was from 1/290 to 1/3,700 for IgM, and from 1/920 to 1/3,250 for IgG secretion. PWM activated from 1/140 to 1/3,200 B cells to IgM secretion. The results of experiments in which EBV and PWM were mixed, indicated that these two polyclonal activators operated on different B cell subpopulations. Therefore, both these agents seem to activate small, discrete subpopulations of human peripheral blood B cells to Ig secretion.

B-lymphocyte subpopulation which forms rosettes with mouse erythrocytes increased in rheumatoid arthritis

We studied the peripheral blood lymphocytes of 22 patients with rheumatoid arthritis (RA) for the presence of a subpopulation of cells which form rosettes with mouse erythrocytes. In normal subjects these cells have been characterised as immature B cells which are non-responsive to pokeweed mitogen. The mean percentage of mouse rosette-forming cells (MRFC) in the rheumatoid group was 13 +/- 10(mean +/- 2 SD), a significantly higher value than the control mean of 5% +/- 4% (P less than 0.001). The T- and B-cell percentages in the rheumatoid patients were normal. The ratio of MRFC: B cells derived from these results was 3:4 in RA and 1:4 in normal subjects. Pre-incubation of rheumatoid peripheral blood lymphocytes at 4 degrees C gave higher values of MRFC (19% +/- 10%) than pre-incubation at 37 degrees C (13% +/- 10%, P less than 0.02), but no such temperature effect was found in the control group. There was no correlation between MRFC and rheumatoid disease activity or the patients' drug regimens. We conclude that the threefold increase in mean MRFC in patients with rheumatoid arthritis indicates an abnormality in the circulating B-cell pool.