Immunoglobulin production by cultured human lymphocytes

Differential Downstream Effects of Cd40 Ligation Mediated by Membrane or Soluble CD40L and Agonistic Ab: A Study on Purified Human B Cells

With the addition of various cytokines, the CD40-CD40 ligand (CD40L) system can act as a T-helper cell surrogate to permit B lymphocytes to produce large amounts of polyclonal Ig. In the present study, we tested six CD40-CD40L stimulation models: (i, ii) soluble agonistic 89 and G28.5 mAbs; (iii, iv) ‘89’ and ‘G28.5’ bound via their Fc fragments on CDw32-transfected mouse fibroblasts; (v) purified, soluble, trimeric human CD40L molecules (sCD40L); and (vi) human CD40L expressed by a CD40L-transfected mouse fibroblastic cell line (LCD40L). Target B cells consisted of purified blood and tonsillar CD19+ lymphocytes cultured in the presence of CD40 stimuli and IL-2 and IL-10, added at the onset of each B cell culture. A) There was differential expression of CD69, CD80 and CD86 exposure to sCD40L and LCD40L was ensued by the strongest % MFI changes over control. B) In blood B cells, mAbs and sCD40L induced IgA, IgM and IgG production almost equally well; LCD40L proved less efficient. In contrast, in tonsil B cells, LCD40L induced significantly more IgA, IgG 1, IgG3and IgM production than other signals. Using certain CD40/CD40L stimuli to model in vitro Ig production, a system used regularly in many laboratories, may affect the interpretation based on the cell type and on the CD40/CD40L system used.

Abnormal B-cell regulation in highly sensitized patients with sustained serum levels of antibody to HLA class I antigens

BACKGROUND

There are anti-idiotypes in the sera of highly sensitized (HS) patients that stimulate B cells to produce antibody to HLA class I antigens. The purpose of this study is to determine if there is an abnormality in B cell responses to these anti-idiotypes.

METHODS

Supernatants from normal and HS B cells exposed to either HLA-like anti-idiotypes or HS sera were tested for IgG and antibody to HLA class I antigens by ELISA and flow beads.

RESULTS

When stimulated with HS sera, HS B cells produced antibody to HLA class I antigens (in vitro) (12/12) but normal B cells did not (0/10) (P<0.0001). When HS B cells were stimulated with isolated HLA-like anti-idiotypes, they produced more total IgG in the supernatant (603+/-105 ng/ml vs. 293+/-30 ng/ml; P<0.01) and more IgG1 (67+/-5.3 ng/ml vs. 32.3+/-5.4 ng/ml; P<0.001) and more IgG3 (33.3+/-9.2 vs. 2.03+/-0.2 ng/ml; P<0.0001) than normal B cells. The proliferative response to HLA-like anti-idiotypes was 1285+/-115 cpm from normal B cells and 1020+/-445 from HS B cells (p=NS).

CONCLUSIONS

When exposed to HS sera, HS B cells produced antibody to HLA class I antigens and normal B cells did not. When exposed to isolated HLA-like anti-idiotypes, HS B cells produced more total IgG, primarily IgG1 and IgG3 with normal proliferation. This intrinsic abnormality in HS B cells permits antibody to HLA class I antigens to be produced and allows increased amounts of IgG1 and IgG3 to be secreted in the absence of an increase in proliferation.

Measurement of Immunoglobulins G, A, and M Levels in B‐Lymphocytes Culture

Nephelometric immunoassays were developed for human IgG, IgA, and IgM quantitation in B-lymphocytes culture media. They allowed measurement of immunoglobulin (Ig) levels over a broad range of concentrations with good accuracy and precision. The kinetics of Ig production in B-lymphocyte cultures was followed and the mean amount of each Ig was determined in six different samples after three days of culture. The nephelometric immunoassays reported here could be used to study, in vitro, the influence of various molecules (inhibitory or amplifying effect) on B-lymphocytes' functional capacities.

CD40 Stimulation of Human Peripheral B Lymphocytes: Distinct Response from Naive and Memory Cells

During secondary immune response, memory B lymphocytes proliferate and differentiate into Ig-secreting cells. In mice, the binding of CD40 by CD154 clearly enhances the activation and differentiation of memory B lymphocytes. In humans, the role of CD40-CD154 in the stimulation of memory B lymphocytes is not as obvious since in vitro studies reported positive and negative effects on their proliferation and differentiation in Ig-secreting cells. In this study, we examine the response of peripheral memory and naive cells in relation to the duration of CD40-CD154 interaction. We measured the proliferation and differentiation of both subsets stimulated with CD154 and IL-4 for short- (4-5 days) and long-term (>7 days) periods. Following short-term stimulation, memory B lymphocytes did not expand but represented the only subset differentiating into IgG- and IgM-secreting cells. A longer stimulation of this population led to cell death, while promoting naive B lymphocyte proliferation, expansion, and differentiation into IgM- or IgG-secreting cells. This prolonged CD40 stimulation also triggered naive B lymphocytes to switch to IgG and to express CD27 even in absence of somatic hypermutation, suggesting that these latter events could be independent. This study suggests that naive and memory B lymphocytes have distinct requirements to engage an immune response, reflecting their different roles in humoral immunity.

Anti-Saccharomyces cerevisiae antibodies: a stable marker for Crohn's disease during steroid and 5-aminosalicylic acid treatment

OBJECTIVES

An increased prevalence of elevated serum anti-Saccharomyces cerevisiae antibody (ASCA) levels in patients with Crohn's disease (CD) has been described. The aim of the present work was to investigate serum ASCA levels during the courses of prednisolone and mesalamine therapy in CD patients.

METHODS

Serum samples of 25 patients with active CD were studied for ASCA levels before as well as 2 and 9 wk after initiation of a prednisolone tapering regimen. The influence of mesalamine (4 g o.d.) on serum ASCA levels compared to that of placebo was tested over 1 yr in 38 patients (20 mesalamine and 18 placebo) participating in a postoperative prophylaxis study. Serum IgG and IgA ASCA levels were measured by ELISA. Sera of 91 CD and 40 ulcerative colitis (UC) patients as well as 334 healthy donors were tested for ASCA to recalculate new cut-off values.

RESULTS

For IgG ASCA cut-off values were determined to be 17.0 U and 25.0 U, and for IgA ASCA 9.3 U and 14.0 U. At baseline visit, 73.0% (46/63) of patients displayed serum ASCA positivity. During prednisolone therapy, a decrease in serum IgG and IgA ASCA levels from baseline to wk 2 (p < 0.0001 and p < 0.001, respectively) as well as to wk 9 (p < 0.001 and p = 0.01, respectively) was observed. A trend toward an association of ASCA positivity and steroid responsiveness was calculated (p = 0.07). During mesalamine treatment, no differences in changes of ASCA levels were observed compared to placebo at any time point.

CONCLUSIONS

ASCA are stable markers during steroid and mesalamine treatment, highlighting their reliability for use in diagnosis of CD.

Adaptation of Cell Lines to Serum-Free Culture Medium

The optimum conditions to allow proliferation of cells for the secretion of some growth factors and cytokines and the proliferation of cells in different media that do not contain proteins or serum from animals (serum-free media) were investigated. The culture of cell lines for the commercial production of products involves optimisation of cell proliferation and secretion in media from which the requisite proteins can be economically extracted. Some of these problems were addressed in this study. We used two different clones from a human myeloma cell line for adaptation to serum free medium in order to characterize long-term effects of the new medium. We gradually decreased serum content of medium and the results showed that cell mortality increased with serum reduction, antibody production lost by survived clones, and secretion of cytokines were always retained.

HIV-gp160 modulates differentially the production in vitro of IgG, IgA and cytokines by blood and tonsil B lymphocytes from HIV-negative individuals

HIV1-gp160 holds promises in anti-HIV vaccinal strategies. However, this molecule has been described to exhibit superantigenic activities. The present study aimed at examining the effect(s) of HIV1-gp160 on human B cells and in particular on B cells originating from HIV- donors. We purified human B cells of various origins, i.e. from blood and from tonsils (representing a mucosal-type origin), and we tested these cells (stimulated with a polyclonal B cell activator, interleukin (IL)-2 and IL-10 as cytokines, and recombinant HIV1-gp160) for the production of IgG and IgA in an in vitro model. Gp160 induced significantly less total IgG by blood - but not tonsil-originating - B cells and did not affect total IgA production. Further, HIV1-gp160 up-regulated IL-2-, IL-4- and IL-10-mRNA levels in stimulated blood B cells (these cytokines are known to be active on B cell activation and differentiation). Interestingly, HIV1-gp160 also up-regulated IL-1beta-, transforming growth factor (TGF)-beta-, interferon (IFN)-gamma- and IL-12-mRNA levels in stimulated mucosal-type, tonsil-originating, B cells. As these latter cytokines are involved in proinflammatory activities, HIV-gp160 delivery at the mucosal sites would be compatible with an adjuvant activity.

Cytokine secretion by peripheral blood mononuclear cells in myasthenia gravis

We studied spontaneous secretion of anti-acetylcholine receptor antibody (AChRAb), IgG and cytokines by peripheral blood mononuclear cells (PBMC) from 19 MG patients without therapy and 10 normal controls. IgG secretion was higher in the culture medium of MG than in that of normal controls. AChRAb secretion was correlated with IgG secretion in MG. Interleukin (IL)-2, IL-4, IL-5, IL-6, IL-10, IL-13, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha secreted by PBMC from MG patients were not different from those produced by those from normal controls. IgG secretion was, however, correlated with the secretions of IL-5 and IL-6 in MG. Spontaneous B cell activation was suspected in patients with MG.

CD19+ B lymphocytes are the major source of human antibody-secreting hybridomas generated by electrofusion

Human monoclonal antibodies may be generated by electrofusion of human B lymphocytes with a human/mouse heteromyeloma line. In addition to a fusion protocol optimised for the fusion partners, the activation of B lymphocytes is crucial for fusion and hybrid efficiency. In this study, we initially treated peripheral blood mononuclear cells (PBMC) from normal blood donors with a large panel of known stimulants and determined the yield of human antibody-secreting hybridomas after electrofusion with the heteromyeloma cell line H73C11; 3- to 5-day incubation with phytohaemagglutinin L (PHA-L) resulted in the highest number of secreting hybrids. In a second set of experiments, PBMC were depleted from various cell populations, including CD14+ monocytes, CD8+ T lymphocytes, and CD2+ T cells, respectively. Undepleted PBMC stimulated with PHA-L were shown to give rise to the highest number of secreting hybridomas when subjected to electrofusion, whereas depletion of CD2+ T lymphocytes greatly reduced the yield. In a final set of experiments, CD19+ B lymphocytes were identified as the major source of secreting hybridomas. For optimal fusion efficiency, CD19+ B cells were shown to require direct physical contact with other cell populations, most probably T lymphocytes, during the stimulation process. Our data highlight the importance of an adequate stimulation prior to electrofusion and may be helpful to further facilitate the development of human monoclonal antibodies.