B cell differentiation and immunoregulatory T cell function in human cord blood lymphocytes

The role of B cell differentiation factors and specific T cell help in the pathogenesis of primary hypogammaglobulinemia

We have examined the function of T and B cells from patients with late onset primary acquired hypogammaglobulinemia (PHG). T cells from these patients give effective help to normal B cells for antigen-dependent antibody synthesis. PHG mononuclear cells also synthesize normal quantities of B cell differentiation factors, which enhance IgG, IgM and antigen-dependent antibody synthesis by normal lymphocytes. While patient T cells appear to behave appropriately, the responsiveness of patient B cells is abnormal. Although they respond to differentiation factors with increased synthesis of IgM, overall levels are 10-50-fold lower than normal B cells, and they produce little or no IgG. This pattern of response is not altered if normal T cells are the source of help. The poor response of the B cell appears to represent immaturity rather than an inherent defect, as IgG-secreting clones can be obtained after Epstein-Barr virus transformation of lymphocytes from certain patients, and some of these clones respond to differentiation factors with increased IgG production. The lack of any functional defect in the T population, and the apparent immaturity rather than abnormality of the B cells, may implicate accessory cells in the pathogenesis of the disease.

Control of polyclonal immunoglobulin production from human lymphocytes by leukotrienes; leukotriene B4 induces an OKT8(+), radiosensitive suppressor cell from resting, human OKT8(-) T cells

We report that leukotriene B4 (LTB4), a 5-lipoxygenase metabolite of arachidonic acid, is a potent suppressor of polyclonal Ig production in pokeweed mitogen (PWM)-stimulated cultures of human peripheral blood lymphocytes, while LTC4 and LTD4 have little activity in this system. Preincubation of T cells with LTB4 in nanomolar to picomolar concentrations rendered these cells suppressive of Ig production in subsequent PWM-stimulated cultures of fresh, autologous B + T cells. This LTB4-induced suppressor cell was radiosensitive, and its generation could be blocked by cyclohexamide but not by mitomycin C. The LTB4-induced suppressor cell was OKT8(+), while the precursor for the cell could be OKT8(-). The incubation of OKT8(-) T cells with LTB4 for 18 h resulted in the appearance of the OKT8(+) on 10-20% of the cells, and this could be blocked by cyclohexamide but not by mitomycin C. Thus, LTB4 in very low concentrations induces a radiosensitive OKT8(+) suppressor cell from OKT8(-) cells. In this regard, LTB4 is three to six orders of magnitude more potent than any endogenous hormonal inducer of suppressor cells previously described. Glucocorticosteroids, which block suppressor cell induction in many systems, may act by inhibiting endogenous production of LTB4.

Immunoregulatory function of human cord blood lymphocytes on immunoglobulin production

The functional maturity of human umbilical cord blood B lymphocytes and the immunoregulatory activity of cord T lymphocytes were assessed by measuring the in vitro immunoglobulin production by B cells from either cord or adult blood. Supernatants from 48-hr pokeweed-mitogen (PWM) stimulated cord or adult lymphocyte cultures were added to cord or adult B cell cultures in the presence of PWM; a significant amount of immunoglobulin was produced in adult B cell cultures only. Adult B or T cells were then cocultured with cord T or B cells; a significant amount of immunoglobulin was again found only in adult B cell cultures. These results indicated that cord B cells were functionally immature and that cord helper T cell function was adequate but masked by excessive suppressor activity. Indeed, addition of cord T cells but not of allogeneic adult T cells to PWM stimulated adult lymphocyte cultures inhibited their immunoglobulin production; this confirmed cord T cells' increased suppressor activity. Cord T cells were not intrinsically suppressive since they failed to suppress immunoglobulin production by Epstein-Barr Virus (EBV) transformed B cells. They could be activated, however, by PWM or allogeneic cells (in mixed lymphocyte cultures) and their effect was mediated via soluble factor(s) as demonstrated by the suppressor effect of these culture supernatants on immunoglobulin production by unfractionated adult lymphocytes. In contrast, when these supernatants were added to T cell-depleted adult lymphocyte cultures, enhancement rather than suppression was observed. These results indicated that the soluble factor(s) released by Cord T lymphocytes was not suppressing per se but induced suppression through activation of suppressor cells.

Cord blood B cell differentiation. Synergistic effect of pokeweed mitogen and Staphylococcus aureus on in vitro differentiation of B cells from human neonates

B lymphocyte differentiation into immunoglobulin secreting cells is a process depending on the presence of functionally mature B lymphocytes, monocytes and regulatory T lymphocytes. Cord blood B lymphocytes present in isolated cord blood mononuclear cell (MNC) preparations are normally unable to differentiate into immunoglobulin secreting plaque forming cells (PFC) when cultured in the presence of pokeweed mitogen (PWM) alone or killed Staphylococcus aureus Cowan 1 (SAC1) alone. However, each one of these activators induces PFC formation by B lymphocytes in adult MNC cultures. In the present study we show that these two activators can act synergistically to induce a significant in vitro PFC response in cord blood MNC's. The synergism of PWM and SAC1 exhibits a requirement for a specific sequence of addition in order to induce a positive response in neonatal cells. If both activators are not added simultaneously at the initiation of culture, only the initial addition of SAC1 followed by PWM will result in increased PFC production. The action of PWM and SAC1 on cord blood MNC can each be replaced by conditioned media. Supernatants from monocyte cultures containing soluble factors such as interleukin-1 (IL-1) can substitute for the activity of SAC1 while supernatants containing soluble T-cell factors (interleukin-2[IL-2], T cell replacing factor (TRF), B cell differentiation factor (BCDF), etc) can replace PWM in the cord blood MNC cultures. The results suggest that the synergistic effect of these two activators overcomes a partial immaturity or an excessive suppressor activity of human cord blood MNC.

Excessive numbers and activity of peripheral blood B cells in infants with Chlamydia trachomatis pneumonia

The peripheral blood lymphocytes of seven infants who had lower respiratory infections caused by Chlamydia trachomatis (chlamydial pneumonia) were studied for abnormalities that may be related to the hyperimmunoglobulinemia characteristic of this infection. Both proportions and numbers of B cells and plasma cells were strikingly elevated in these infants, as indicted by the percentage of peripheral blood mononuclear cells (PBMC) that reacted with fluorochrome-labeled antibodies to human immunoglobulins. Cells expressing IgM and IgD on their surface, and cells possessing IgM and IgG in their cytoplasm were especially increased above levels found in normal adults, infants, and a group of infants with other infections. Cells from infected infants secreted exceptionally large amounts of IgM, IgG, and IgA when cultured in the absence of added mitogens. These data suggest that chlamydial pneumonia induces substantial B-cell activation during a period of development when antibody responses are normally difficult to stimulate.

In vitro X-ray irradiation of human peripheral blood T lymphocytes enhances suppressor function

We studied the effect of in vitro X-ray irradiation on human peripheral blood T lymphocytes, with regard to their suppressor activity related to the concanavalin A (Con A)-induced suppressor system. To generate suppressor T lymphocytes, purified human T lymphocytes were incubated for 3 days in the first culture, with or without Con A. These lymphocytes were irradiated with various doses of X-ray before, mid or after the culture. After doing a second culture for 6 days, we measured the suppressive influence of these cells on T lymphocyte proliferation rates stimulated with allogeneic mononuclear cells, and B lymphocyte proliferation rates stimulated with pokeweed mitogen. Irradiation (1,000 rad) of cultures to which Con A had not been added induced much the same level of suppressor activity as seen in the cultures with Con A. The suppressor activity gradually increased with lapse of time from the irradiation to the suppressor cell assay. Suppressor T lymphocytes were resistant to X-ray irradiation and independent of DNA synthesis. On the other hand, irradiation-induced enhancement was minimal in cultures incubated with Con A, regardless of the irradiation time. As irradiation of human peripheral blood T lymphocytes was found to induce a suppressor function in vitro, clinical and experimental applications of irradiation in cases of a suppressed T lymphocyte function may be feasible.

Antigen-specific plaque-forming cell response of human cord blood lymphocytes after in vitro stimulation by T cell-dependent antigens

Mononuclear cells isolated from human cord blood (CBL) of full-term neonates were stimulated in vitro with a dose range of T cell-dependent antigens, i.e. ovalbumin or sheep erythrocytes, and tested for the capacity to mount an antigen-specific plaque-forming cell (PFC) response. Both of the antigens used induced in CBL a PFC response with the same kinetics of PFC formation and of the same magnitude as found in cultures of adult peripheral blood lymphocytes (PBL). However, optimal PFC responses in CBL were obtained at a hundredfold lower concentration of the antigens compared with the optimal antigen doses for the induction of a PFC response in adult PBL. This phenomenon was further investigated with respect to the antigen dose dependency of the activation of neonatal B cells and neonatal regulatory T cells. The induction of a PFC response in CBL at antigen concentrations that were suboptimal for adult PBL showed a correlation with the particular antigen dose requirements for the activation of B cells and T helper cells in neonates. Furthermore, the findings suggest that the decrease of the PFC response in CBL stimulated with supraoptimal doses of antigen was not caused by the induction of unresponsiveness at the B cell level or by interference of pregnancy-associated substances with the PFC response, but was rather the result of the activation of antigen-specific T suppressor cells. Neonatal T suppressor cells were activated at antigen concentrations that generated T helper activity in the adult. Thus, although neonatal B cells possess the intrinsic capacity to mature into antigen-specific PFC, the conditions for effective activation of neonatal T cells regulating the B cell response differ from those for the activation of adult regulatory T cells.

Suppression of B lymphocytes in mature newborn infants

The ability of cord blood lymphocytes to secrete immunoglobulins during in vitro culture was investigated by means of a reverse hemolytic plaque forming cell (PFC) assay. Mononuclear cord blood cells did not differentiate into immunoglobulin-secreting cells after stimulation with the polyclonal B lymphocyte activator pokeweed mitogen (PWM), contrary to the findings in normal adults. Mononuclear cord blood cells were then separated into T-enriched and T-depleted blood lymphocyte subsets. When these were co-cultured, the PWM-induced immunoglobulin secretion was still low; following irradiation of the T-enriched cells, the numbers of IgM-PFC but not of IgG- or IgA-PFC increased considerably. The effect of irradiation of the T-enriched cells on the PWM-induced IgM response was dose-dependent, with maximal effect at 2500 rad. It is concluded that the low PWM responses obtained using cord blood lymphocytes are in part due to suppression by radiosensitive T suppressor cells. Following removal of this suppression by means of irradiation, B lymphocytes can be induced to secrete IgM, but not IgG or IgA.

Limiting dilution analysis of Epstein-Barr virus-induced immunoglobulin production by human B cells

The Epstein-Barr virus (EBV) is a herpes virus that has the capacity to infect human B cells and to induce them to secrete immunoglobulin (Ig). In the current experiments, Poisson analysis of limiting dilution cultures has been used to study the activation of human peripheral B cells by the B95-8 strain of EBV. Under the culture conditions used, 0.2-1% of peripheral blood B cells were activated by EBV to secrete IgM or IgG. In addition, when multiple replicate cultures containing limited numbers of B cells were tested for IgM and for IgG production, the precursors for IgM and IgG segregated independently; thus, individual B cell precursors matured into cells secreting IgM or IgG but not both classes of Ig. Additional experiments using limiting dilutions of EBV were undertaken to study the viral requirements for B cell activation. These studies indicated that B cell activation by EBV to produce Ig was consistent with a "one-hit" model and inconsistent with a "two-hit" model. Taken together, these results indicate that infection by one EBV virion is sufficient to induce a precursor peripheral blood B cell to secrete Ig and that only one isotype of Ig is then secreted.

Impaired T-lymphocyte colony formation by cord blood mononuclear cells

When compared to adult mononuclear cells, cord blood mononuclear cells demonstrated significantly decreased T-lymphocyte colony formation (1351 +/- 643 vs 592 +/- 862, P less than 0.01). This diminished colony-forming activity did not appear to be associated with impaired responsiveness to the stimulant phytohemagglutinin or with excessive suppressor-cell activity. Irradiation reduced the colony-forming capacity of cord blood mononuclear cells more than it did that of adult mononuclear cells. Depletion of adherent cells reduced cord blood mononuclear-cell colony-forming capacity by 40%, while similar treatment reduced adult colony formation by 10%. Lymphocyte proliferation in liquid culture of cord and adult cells was minimally affected by these procedures. The colony-forming capacity of cord blood could be enhanced by the addition of irradiated adult cells (284 +/- 72 vs 752 +/- 78, P less than 0.01). This enhancement was demonstrated to be due to a soluble factor produced by a population of irradiated adult cells depleted of the OKT8+ subpopulation of lymphocytes. These results indicate that the progenitor cells of T-lymphocyte colonies in cord blood have distinct biologic characteristics when compared to colony progenitors present in adult blood. This assay may prove to be useful in our efforts to understand the differentiation of T-cell function in man.

Immature B cells in fetal development and immunodeficiency: studies of IgM, IgG, IgA and IgD production in vitro using Epstein-Barr virus activation

Epstein-Barr virus has been used as a B cell mitogen to explore the parallels between the B cells found in patients with hypogammaglobulinemia and the immature B cells in fetal tissues. Peripheral blood lymphocytes from 29 cases of late onset hypogammaglobulinemia (common variable immunodeficiency) and from 10 cases of X-linked hypogammaglobulinemia were depleted of T lymphocytes and stimulated with virus in vitro. Immunoglobulin production was measured over a 4-week culture period using inhibition radioimmunoassays for IgM, IgG, IgA and IgD. The results were compared with those seen with fetal liver cells, cord blood lymphocytes and adult lymphocytes. Virus-stimulated cells from fetal sources produced small amounts of IgG and IgA relative to IgM, the ratio of IgM to IgG in the second week being in all cases greater than 10. Similar patterns were seen in 25/29 cases of late onset hypogammaglobulinemia, and in the eight cases of X-linked hypogammaglobulinemia that responded in vitro. In contrast, the ratio of IgM to IgG was always less than 8 in cultures of normal adult peripheral blood or bone marrow lymphocytes, and also in cultures from four cases of hypogammaglobulinemia known independently to have abnormal circulating suppressor cells. Eight cases of selective IgA deficiency showed reduced IgA production; six of these showed a normal ratio of IgM to IgG production. Thus, the B lymphocytes which circulate in many patients with hypogammaglobulinemia are functionally immature.

Human T-cell subset requirements for the production of specific anti-influenza virus antibody in vitro

Studies were undertaken to define the helper T-cell requirements for in vitro specific antibody production to influenza virus. Subpopulations of human T cells were separated on the basis of their reactivity with the monoclonal antibody OKT4. B cells cultured with OKT4+ T cells produced specific antibody to influenza virus, while B cells cultured with OKT4- T cells did not. Irradiation (1200 rads) of the OKT4- subset to potentially eliminate suppressor-cell activity did not augment the helper-cell function of that subset. Thus, unlike the cytotoxic T-cell response to influenza, help for an in vitro antibody response is mediated only by OKT4+ T cells.

Reactivation of Epstein-Barr virus in pregnant women: social factors, and immune competence as determinants of lymphoproliferative diseases-a hypothesis

In normal pregnant women, reactivation of Epstein-Barr virus (EBV) frequently occurs. Cellular immune responses are apparently suppressed, but high titer EBV-specific antibodies of IgG class may compensate. The antibodies cross the placenta and protect the infant against primary infection for many months. Reactivation of EBV in pregnancy and oral excretion of virus by normal pregnant women could be one explanation why young children in large sibships (among families of low social classes) become infected early in life. Infants are likely infected by EBV from their pregnant mothers who shed virus in saliva. Moreover, the natural protection for several months in the perinatal period against Burkitt lymphoma and fatal EBV-induced lymphoproliferative diseases in congenitally immune deficient children is explained. The maturity and immunocompetence of the immune system at the time of primary infection by EBV and the size of the sibship seem to determine whether infectious mononucleosis occurs. Gammaglobulin derived from human cord blood may be a valuable source of viral-specific antibodies for serotherapy in immune deficient patients.

Fetal cytotoxic antibodies to maternal T-lymphocytes: a possible mechanisms for maternal tolerance of the fetal allograft

The absolute numbers of B lymphocytes and of total and "active" T lymphocytes in peripheral venous blood (Mv) from 15 females at the time of normal term deliveries were found to be significantly less (p less than 0.001) than in the fetal umbilical vein (Uv) or artery (Ua) or in the peripheral blood of 75 normal nonpregnant controls (Cv), suggesting that maternal cellular immunity at term is lowered. In 19 umbilical artery samples, titers of lymphocytotoxic antibodies (Cyt), expressed as the mean log of reciprocal titer values, were significantly higher (p less than 0.01 in each case)( than in matched maternal samples, against the following cell types: Maternal T cells (7.1 in Ua vs 1.21 in Mv sera); maternal B cells (3.23 vs 1.58); T cells (4.41 vs 1.38) but not B cells from other females at delivery; autologous T cells (2.9 vs 1.0); autologous B cells (1.88 vs 0.69); T (5.39 vs 0.81) and B (2.80 vs 1.25) cells from the paired Uv; T (3.78 vs 0.62) and B (2.64 vs 0.77) cells from the Uv of other newborn infants; and T (4.19 vs 2.0) but not B cells from controls (Cv). The highest Cyt titers in the umbilical artery samples were against maternal T lymphocytes. Immunofluorescence studies indicated that the Cyt antibodies were primarily IgG. Absorption of 13 other Ua sera with maternal T cells eliminated with Cyt activity against both Mv and Cv T cells; absorption with Cv T cells eliminated the reaction against Cv T while reducing cyt titres to Mv T lymphocytes. We conclude that the fetus produces lymphocytotoxic antibody specifically directed against maternal T lymphocytes, in addition to antibody against T lymphocytes of other adults.

Characterization of the suppressor cell activity in human cord blood lymphocytes

Newborn mononuclear cells are known to have increased suppressor activity when compared with adult cells. However, the precise phenotypic description of the suppressor cell subpopulation has not yet been reported. This study was designed to examine the surface markers on human cord blood cells as defined by monoclonal antibodies and to characterize cord blood mononuclear cells that suppress in vitro pokeweed mitogen-driven immunoglobulin production. The pattern of fluorescence with the 9,6-monoclonal antibody suggested either a decreased density or a partial blocking of E-receptors on cord blood lymphocytes. Otherwise, human cord and adult cells had similar proportions of T cell subpopulations. Different subsets of newborn cells isolated by a monoclonal antibody rosetting technique were tested for suppressor activity. Cord blood lymphocytes recognized by the OKT8 monoclonal antibody constituted the major functional suppressor cell subpopulation. These cells were present in both E-rosetting and non-E-rosetting populations. Removal of OKT8+ mononuclear cord blood cells abrogated most of the suppressor activity. Thus the major suppressor cell present in cord blood is an OKT8 positive lymphocyte.

Immunoglobulin production induced in vitro by glucocorticoid hormones: T cell-dependent stimulation of immunoglobulin production without B cell proliferation in cultures of human peripheral blood lymphocytes

The direct effects of steroid hormones on the production of immunoglobulins and DNA synthesis by human T and B lymphocytes was evaluated in cultures of peripheral blood mononuclear cells. As detected by a reverse hemolytic plaque assay, the addition of 0.1 mM to 10 nM hydrocortisone to lymphocytes in culture in the absence of other stimulants or mitogens, resulted in the dramatic induction of immunoglobulin production with responses comparable to those seen in similar cultures stimulated with pokeweed mitogen. Steroid-stimulated immunoglobulin production was first seen after 48 h and peaked at 8-10 d of culture. The production of IgG, IgA, and IgM was induced following incubation with steroid. Glucocorticoids, but not estrogens or androgens, were capable of mediating this effect, and only compounds with affinity for the glucocorticoid receptor were active. The induction of immunoglobulin production was dependent on both T cells and monocytes; cultures depleted of either cell type did not produce immunoglobulin when stimulated with glucocorticoid hormones. Proliferation of B cells or T cells could not be detected by [3H]thymidine incorporation or total cell recovery from steroid-stimulated cultures, even though such cultures demonstrated marked increases in immunoglobulin production. The mechanism responsible for this functional maturation of B cells to become high rate immunoglobulin producing cells is as yet undefined, although it appears to involve more than merely steroid mediated inactivation of suppressor T cells.

Defective EBV-specific suppressor T-cell function in rheumatoid arthritis

Several lines of evidence, including high antibody titers to Epstein-Barr virus (EBV)-associated antigens and rapid transformation of B cells into lymphoblastoid cells lines, suggest an association between EBV and rheumatoid arthritis. When lymphocytes from normal immune donors were infected with EBV in culture, they produced an exponentially increasing number of immunoglobulin-secreting cells for eight to 10 days. Thereafter, there was a marked late suppression of their response, mediated by immunoregulatory T cells; by 12 days in culture, this suppression averaged 90 per cent. Lymphocytes from 20 EBV-immune patients with rheumatoid arthritis also responded with increasing production of immunoglobulin-secreting cells, but the late suppression expected in immune donors was absent. Tests of several other T-cell functions in these patients gave normal results, suggesting a more restricted defect in suppressor-T cell function relating specifically to EBV. Since EBV persists in host B cells and thus represents a potential stimulus for immunoglobulin production, this persistence, along with a specific regulatory T-cell defect, may contribute to many of the immune abnormalities underlying rheumatoid arthritis.

A sequential study of human B lymphocyte function from birth to two years of age

The immunoglobulin synthesizing capacity of individual lymphocytes from newborns and infants aged 2, 6, 12 and 24 months respectively has been studied. The technique has been to expose purified lymphocytes to a T lymphocyte dependent (pokeweed mitogen) or a T lymphocyte independent (Epstein-Barr virus) activator of B lymphocytes. Activation has been measured as immunoglobulin secretion of individual B lymphocytes using a hemolytic plaque assay. B lymphocytes from newborns can be made to synthesize IgM at adult levels, but not IgG and IgA. Within 24 months from birth the secretion of IgG has reached adult capacity whereas IgA formation is still diminished. Lymphocytes synthesizing IgG subclasses appear at different times insofar as IgG1 and IgG3 are well demonstrable within 12 months from birth whereas IgG2 and IgG4 has not at all reached adult levels even 24 months after birth. The T lymphocyte dependent activator (pokeweed mitogen) fails to induce immunoglobulin synthesis in peripheral blood lymphocytes from newborns because of a defect helper T cell function. Such T cell capacity appears at the age of 6 months. The data unequivocally demonstrate restricted but definite B lymphocyte functional capacity already at birth and a gradual but partial acquisition of adult competence until the age of 2 years.

Requirement for OKT8+ suppressor cell proliferation for suppression by human newborn T cells

The percentage of cells bearing the suppressor phenotype OKT8+increases in PWM-stimulated cultures of human newborn lymphocytes. Prevention of this increase either by adding 50 microM deoxyguanosine to the cultures of by pretreating the newborn cells with OKT8 and complement reduced the suppressor activity of newborn T cells. These results suggest that newborn T cells are not intrinsically suppressive, but that they become so in vitro after stimulation by PWM.

Free immunoglobulin light chain synthesis by human foetal liver and cord blood lymphocytes

Immunoglobulin (Ig) synthesis by immature B lymphocytes from human foetal liver and cord blood has been investigated. Seven out of fifteen preparations of foetal liver cells and eight out of eleven cord bloods synthesized Ig detectable by biosynthetic labelling. All cultures of foetal lymphocytes with detectable Ig synthesis secreted free light chain. Two of these cases also synthesized free mu heavy chain. Cord blood lymphocyte synthesis patterns were variable ranging from free light chain as the only secreted Ig product to balanced synthesis of heavy and light chains. No cord blood cultures synthesized detectable free mu chains. Free Ig-light-chain synthesis appears to be associated with normal immature B lymphocytes and the results are discussed in relation to the B-cell differentiation pathway.