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Polyclonal preparations of therapeutic immunoglobulins, namely intravenous immunoglobulins (IVIg), are essential in the treatment of immunodeficiency and are increasingly used for the treatment of autoimmune and inflammatory diseases. Currently, patients’ accessibility to IVIg depends exclusively upon volunteer blood donations followed by the fractionation of pooled human plasma obtained from thousands of individuals. Presently, there are no in vitro cell culture procedures allowing the preparation of polyclonal human antibodies. All in vitro human therapeutic antibodies that are currently generated are based on monoclonal antibodies, which are mostly issued from genetic engineering or single cell antibody technologies. Here, we describe an in vitro cell culture system, using CD40-CD154 interactions, that leads to a 1×106-fold expansion of switched memory B lymphocytes in approximately 50 days. These expanded cells secrete polyclonal IgG, which distribution into IgG1, IgG2, IgG3 and IgG4 is similar to that of normal human serum. Such in vitro generated IgG showed relatively low self-reactivity since they interacted moderately with only 24 human antigens among a total of 9484 targets. Furthermore, up to one liter of IgG secreting cells can be produced in about 40 days. This experimental model, providing large-scale expansion of human B lymphocytes, represents a critical step toward the in vitro production of polyclonal human IgG and a new method for the ex vivo expansion of B cells for therapeutic purposes.

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Summary Human B cells can be cultured ex vivo for a few weeks, following stimulation of the CD40 cell surface molecule in the presence of recombinant cytokines such as interleukin‐4 (IL‐4). However, attempts to produce polyclonal antigen‐specific human antibodies by in vitro culture of human B cells obtained from immunized donors have not been successful. It has been shown in mice that lipopolysaccharide (LPS) is a potent mitogen for B cells and plays an important role in the generation of antigen‐specific antibody responses. Although it has long been believed that LPS has no direct effect on human B cells, recent data indicating that IL‐4‐activated human B cells are induced to express Toll‐like receptor‐4, the main LPS receptor, prompted us to study the effects of LPS on the proliferation and antibody secretion of human B cells. Our results showed that LPS caused a reduction in the expansion of CD40‐activated human B cells, accompanied by an increase in antigen‐specific antibody secretion. This result suggested that some, but not all, B cells were able to differentiate into antibody‐secreting cells in response to LPS. This increased differentiation could be explained by the observation that LPS‐stimulated human B cells were induced to secrete higher amounts of IL‐6, a pleiotropic cytokine well‐known for its B‐cell differentiation activity. In vivo, the effect of LPS on cytokine secretion by B cells may not only enhance B‐cell differentiation but also help to sustain a local ongoing immune response to invading Gram‐negative bacteria, until all pathogens have been cleared from the organism.

The relation between the immune response and the clinical features of severe falciparum malaria was studied in Burundian adults with (n = 31) and without (n = 17) cerebral involvement. At the time of admission, mean values for age, temperature, and blood levels of hemoglobin, creatinine, bilirubin, and glucose were similar in the two groups. Plasma levels of tumor necrosis factor alpha, interferon gamma, interleukin 10 (IL-10), and soluble intercellular adhesion molecule 1 were similarly elevated in the two groups. Mean parasite counts and mean plasma levels of soluble E-selectin were higher in severe noncerebral malaria than in cerebral malaria and were correlated with each other. After adjustment for parasitemia, levels of soluble E-selectin remained higher in noncerebral malaria. All seven patients who died had cerebral disease. These patients had higher levels of creatinine, bilirubin, IL-10, and soluble E-selectin than did patients with nonfatal cerebral malaria. After adjustment for creatinine and bilirubin levels, IL-10 and soluble E-selectin concentrations were similar in fatal and nonfatal cases of cerebral infection. In these African adults, none of the immunologic variables investigated was specific to cerebral malaria or to a fatal outcome.