Mechanism of pokeweed mitogen inhibition of rhIL-4-induced human IgE synthesis

Generation of heterohybridomas secreting human immunoglobulins; pokeweed mitogen prestimulation is highly effective but phytohemagglutinin drives most B cells into apoptosis

Human monoclonal antibodies have commonly been generated by forming hybridomas of stable lymphoblastoid cell lines and Epstein-Barr virus (EBV)-transformed human B cells that have been exposed to phytohaemagglutin (PHA)-stimulated T cells. However, this technique has predominantly given rise to IgM- but very rarely IgG- or IgA-producing clones. We now report that, regardless of prior EBV infection, pokeweed mitogen (PWM) stimulation of human peripheral blood mononuclear cells (PBMCs) generated much higher numbers of IgM-, IgA- and IgG-producing B cells than did stimulation with PHA. Fusion of PWM-stimulated PBMCs with a mouse myeloma cell line also gave rise to 7- to 12-fold higher numbers of IgG- and IgA-producing heterohybridomas than PBMCs that were prestimulated with PHA. Judged by Annexin V staining, stimulation with PHA induced a very high rate of B cell apoptosis within 24 h, whereas, even after 7 days, PWM stimulation only induced marginal B cell apoptosis. This should explain why PHA is much inferior to PWM in stimulating immunoglobulin (Ig) production in vitro and in generating immunoglobulin-producing human B cell hybridomas. It is concluded that PWM stimulation may greatly facilitate the generation of human monoclonal antibodies of all isotypes.

Immunoregulatory properties of growth hormone and prolactin

Reciprocal communication between the neuroendocrine and immune systems is critical to the establishment of host homeostatic and defence mechanisms. The production and utilisation of common ligands and their receptors by cells of the immune and neuroendocrine systems constitutes a biochemical information circuit between and within the immune and neuroendocrine systems. Although the structures of the various signalling components appear to be similar in both systems, the regulation of their synthesis may be different. Growth hormone and prolactin have similar and marked influences on the function/activity of each of the major immune cell types, both in vitro and in vivo. The underlying molecular mechanisms are just beginning to be unravelled, and it is anticipated that further work in this rapidly developing field will establish abnormal pituitary and/or lymphocyte growth hormone and prolactin synthesis and function as a contributory factor to a number of pathologic situations, including leukaemia and autoimmunity.

Association of interleukin-2 and interferon-gamma production by blood mononuclear cells in infancy with parental allergy skin tests and with subsequent development of atopy

The mechanisms regulating the onset of atopic sensitization in human beings are not yet fully clarified. We assessed the capacity of mitogen-stimulated umbilical and peripheral blood mononuclear cells to produce interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) at birth and at 9 months of age in 159 infants. Mononuclear cell production of both IFN-gamma and IL-2 at 9 months, but not at birth, was found to be inversely related to parental immediate skin test reactivity to seven local aeroallergens. Skin test reactivity at the age of 6 years was also inversely related to IFN-gamma and IL-2 production at 9 months of age. However, no relationship was evident between total serum IgE levels at 6 years and production of these cytokines at 9 months. The proportions of circulating lymphocytes and CD4+ or CD8+ cells were also unrelated to skin test reactivity at the age of 6 years. These data suggest that mechanisms regulating skin test reactivity to inhaled allergens may involve deficient IFN-gamma production, deficient IL-2 production, or both during or preceding the time of initial sensitization and that additional mechanisms are involved in regulating total serum IgE level.

Growth hormone inhibits normal B-cell differentiation and neutrophils' chemotaxis in vitro

In acromegalic patients we have previously described a low ability of B-lymphocytes to differentiate into plasma cells under PWM stimulation, and a decreased chemotaxis of polymorphonuclear leukocytes (PMN) towards N-formylmethionylphenilalanine (FMP). In this study we examined the effect of exogenous GH over these immune functions in normal cells. PMN were purified by dextran sedimentation, incubated with recombinant human GH (0 to 20 ng/ml) and subjected to stimulation with FMP. PBMC were cultured with or without PWM, in the presence of GH (between 0 and 100 ng/ml). Plasma cells were determined as hemolysis plaque forming cells and also by immunofluorescence. GH, in a dose-dependent way, decreased directed migration of PMN (5 ng/ml: 1.787 +/- 148 microns; 10 ng/ml: 1.581 +/- 221 microns; 20 ng/ml: 1.569 +/- 149 microns, all as mean +/- S.E.M.), when compared to similar values of untreated PMN (0 ng/ml 2.085 +/- 139 microns). GH treatment did not modify spontaneous migration. Net migration showed the same pattern as directed migration. GH decreased dose-dependently the PWM-driven differentiation of B-lymphocytes into plasma cells to 60% of the basal level. Although not significantly, GH tended to increase spontaneous B-cell differentiation. These results could account for the already described defect in B-cell differentiation and PWN chemotaxis in acromegaly, emphasizing the relationship between the endocrine and immune systems.

Neuropeptides are potent modulators of human in vitro immunoglobulin E synthesis

We determined the effect of adrenocorticotropin hormone (ACTH) on the regulation of IgE synthesis. Depending on the concentration, ACTH enhanced or inhibited IgE synthesis in a culture system where IgE synthesis was induced with interleukin-4 (IL-4) and anti-CD40 monoclonal antibody in peripheral blood mononuclear cells. Similar effects on IgE synthesis were observed by adding ACTH-related peptides, e.g. corticotropin-releasing factor (CRF), the inducer of ACTH, or alpha-melanocyte stimulating hormone (alpha-MSH), a cleavage product of ACTH. However, ACTH had no effect on IgG or IgM synthesis in this culture system. ACTH did not act directly on either B or T cells as there was no influence on IgE synthesis in a system using purified B cells alone or co-cultured with T cells. The effect of ACTH on IgE synthesis was mediated by accessory cells. This was shown by priming purified CD14-positive monocytes with ACTH and reconstitution experiments. Therefore, these findings suggest that ACTH and the related peptides CRF and alpha-MSH can influence the microenvironment modulating an IL-4 and anti-CD40 monoclonal antibody driven class switching to IgE via accessory cells.