Irma R. Koski

Activation of Suppressor T Cells during Epstein-Barr-Virus-Induced Infectious Mononucleosis

Infectious mononucleosis is caused by the Epstein-Barr virus (EBV), an unusual human pathogen because it preferentially infects B lymphocytes and consequently activates them to produce immunoglobulins. When cultures of lymphocytes from patients with infectious mononucleosis were stimulated with polyclonal activators, unseparated cells failed to produce immunoglobulins, whereas purified B cells responded normally. Cocultures demonstrated profound suppressor T-cell activity in blood from patients with infectious mononucleosis. Early in this disease, circulating immunoglobulin-secreting cells were elevated, but during the second week their number was strikingly depressed. These data indicate that during infectious mononucleosis, EBV causes polyclonal activation of B cells, reflected by hypergammaglobulinemia and increased circulating immunoglobulin-secreting cells. Next, suppressor T cells become activated and inhibit further B-cell activation. Thus, activation of suppressor T cells in infectious mononucleosis provides a unique additional mechanism of host defense because these T cells inhibit the activation and proliferation of an important target of the causative virus.

B Cell Differentiation and Immunoregulatory T Cell Function in Human Cord Blood Lymphocytes

The functional maturity of T and B lymphocyte populations from human newborns was evaluated using a reverse hemolytic plaque assay to detect immunoglobulin-secreting cells generated in in vitro cultures stimulated with pokeweed mitogen (PWM), a T cell-dependent polyclonal activator, and the Epstein-Barr virus (EBV), a T cell-independent B cell activator. Cord blood lymphocytes failed to produce immunoglobulin in response to PWM, but did respond with immunoglobulin synthesis to stimulation with EBV. Co-culture experiments demonstrated that cord blood T cells would inhibit immunoglobulin production by adult cells stimulated with PWM, but not with EBV. Cord blood T cells did suppress immunoglobulin production by cord blood B cells when stimulated with a mixture of EBV and PWM, indicating that cord blood, in contrast to adult blood, contains a population of suppressor T cell precursors that are easily activated by PWM. Irradiation of the cord blood T cells with 2,000 rad eliminated the suppressor activity and revealed normal helper function for immunoglobulin (Ig) G, A, and M when these T cells were co-cultured with adult B cells. Cord blood B cells co-cultured with adult T cells or irradiated cord blood T cells did produce immunoglobulin in response to PWM, but the response was significantly lower than that of adult B cells, and only IgM was produced in these cultures. These studies demonstrate that both the T and B cells of the human newborn have significant functional differences compared with the functions of T and B lymphocyte populations in adults.

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.

Infectious Agammaglobulinemia: Suppressor T Cells with Specificity for Individual Immunoglobulin Classes

Immunoregulatory cells with potent suppressive effects on immunoglobulin or specific antibody production have been described in many experimental systems. In the chicken, bone marrow cells from adult birds rendered agammaglobulinemic by bursectomy and irradiation at hatching will induce agammaglobulinemia in recipients when transplanted into normal adult chickens of the same strain (1). This “infectious agammaglobulinemia” is induced by donor suppressor T cells which appear in the donor birds in detectable quantities by about 10 weeks of age. Suppressor cells can be demonstrated in spleen, thymus and peripheral blood in addition to bone marrow. The immunodeficiency which develops in the recipient chickens is characterized by their failure to produce specific antibody after challenge with any of several thymic dependent or thymic independent antigens, the rapid disappearance of existing serum IgG, IgA and IgM, the persistence of an intact bursa of Fabricius, and the persistence of a normal number of B lymphocytes in the spleen of these birds at least until after serum immunoglobulin has become undetectable (2, 3, 4).

920 EFFECTS OF STEROID HORMONES ON IMMUNOGLOBULIN PRODUCTION IN ADULT AMD CORD BLOOD LYMPHOCYTES

The effect of steroid compounds on the in vitro production of immunoglobulins was evaluated in cultures of peripheral blood mononuclear cells (PBMC). In a reverse hemolytic plaque assay the addition of 10-5 to 10-8 M hydrocortisone to adult PBMCs in the absence of other stimulants or mitogens resulted in the dramatic induction of immunoglobulin secreting cells (IgSC). This response ranged from a 2-70 fold increase, comparable to or greater than that produced by pokeweed mitogen. Stimulation of IgSC by steroids was first seen after 48 hrs in culture and peaked at 8-10 days. IgG, IgA, and IgM production were all enhanced. All gluocorticoids evaluated, but not androgens, estrogens or steroids not binding to the glucocorticoid receptor, were capable of mediating this effect. The induction of IgSC was dependent on both T cells and monocytes. Glucocorticoids did not stimulate a detectable proliferative response in the cultures. In contrast to the above findings with adult cells, no enhancement of IgSC production could be demonstrated by cord blood lymphocytes at any time during culture or at any dose of steroid compound evaluated. Cord blood could produce IgSC when stimulated with Epstein-Barr virus. The capacity of glucocorticoids to stimulate functional maturation of adult B cells to become IgSC in the absence of cellular proliferation, while being unable to stimulate cord blood B cells, suggests that glucocorticoids may be functioning as maturation agents for memory B cells.

STUDIES OF MONOCYTE Fc RECEPTOR AVIDITY AND MONOCYTE MEDIATED ANTIBODY DEPENDENT CELLULAR CYTOTOXICITY (MMADCC) IN MAN

Publisher Summary This chapter presents an investigation of monocyte Fc receptor avidity and monocyte-mediated antibody-dependent cellular cytotoxicity (MMADCC) in man. Peripheral blood monocytes from normal subjects and patients with various immunodeficiency diseases, including the Wiskott–Aldrich syndrome (WAS) and intestinal lymphangiectasia (IL), were studied in an analysis presented in the chapter. In addition, pleural fluid macrophages were studied in one patient with IL. Mononuclear cells were incubated with 51Cr-labeled human blood group B erythrocytes in the presence of human anti-blood group B antiserum and the number of targets killed determined from the specific release of 5lCr into the medium. In this system, monocytes but not lymphocytes act as effector cells and the amount of killing observed correlates with the number of monocytes in the mononuclear cell effector population. The results showed that MMADCC requires the Fc portion of the antibody. However, as seen in the WAS patients, binding of the antibody-coated target to the monocyte is not in itself sufficient for lysis to occur, indicating that while antibody dependent cellular cytotoxicity requires an Fc receptor, the mere presence of a functional Fc receptor is not enough to trigger the cytotoxic event.

IMMUNOGLOBULIN CLASS SPECIFIC SUPPRESSOR T CELLS

Publisher Summary This chapter describes a few studies demonstrating suppressor cells specific for each of the major immunoglobulin classes as revealed by limiting dilution transfer experiments. Inbred line 6, subline chickens were surgically bursectomized and given 550R whole body irradiation on the day after hatching. Agaranaglobulinemia develops in approximately 90% of the birds by 6 weeks of age. Suspensions of spleen, thymus, bone marrow, and peripheral blood mononuclear cells were obtained from these aγ birds at 4 months of age and were given in various dilutions intravenously to normal 2- or 20-week old chickens of the same strain. Serum immunoglobulin levels were measured in the recipient birds using radial diffusion in agar, and the presence of B lymphocytes in the spleens of these birds was measured by immunofluorescence with FITC conjugated rabbit antichicken immunoglobulin antisera. It was found that 20-week old recipient chickens had normal levels of IgG, IgA, and IgM prior to the injection of aγ lymphoid cells. Within 24 h of cell transfer, all classes of immunoglobulin began to disappear from the serum of these birds so that total agammglobulinemia was present by 45 days after transplant.