The lymphokine B-cell stimulatory factor 1 (BSF-1) has been shown to greatly enhance the differentiation of lipopolysaccharide-activated B cells into IgGl-and IgEsecreting cells in vitro. To determine whether in vivo IgG1 and IgE antibody responses are BSF-1 dependent, the ability of a monoclonal rat IgG1 anti-BSF-1 antibody, 11B11, to affect polyclonal IgG1 and IgE production in mice infected with the nematode parasite Nippostrongylus brasiliensis or iIiected with a purified goat antibody to mouse IgD was studied. 11B11-containing ascites fluid or purified 11B11 strongly inhibited IgE production in both systems but did not affect IgG1 production, while control ascites or normal rat IgG1 had no IgE-inhibitory activity. These results indicate an important physiologic role for BSF-1 in the generation of IgE antibody responses and suggest means for limiting the production of antibodies responsible for allergic reactions without inhibiting protective antibody responses.IgE has a crucial role in the pathogenesis of allergic reactions (1, 2), is thought to be important for host elimination of helminthic parasites (3-5), and is produced in relatively large quantities by animals infected with these parasites (6)(7)(8)(9). The generation of IgE-secreting cells has been shown to be dependent upon helper T lymphocytes (10); no IgE secretion is seen in parasite-infected congenitally athymic (nude) mice (11, 12) or parasite-infected mice injected with a monoclonal antibody (anti-L3T4) (13) that blocks helper T-cell function (14). The nature of the T-cell help required for the generation of an IgE response in vivo is not certain, but soluble, T-cell-produced, IgE binding factors have been shown to modulate in vitro generated IgE responses (15). The demonstration that a purified murine T-cell lymphokine, B-cell stimulatory factor 1 (BSF-1)1 (17,18), is capable of inducing a greater than 100-fold increase in IgE secretion in vitro by lipopolysaccharide-activated mouse splenic B-cell blasts (19), suggested that this lymphokine might be important in the in vivo stimulation of IgE secretion. This led us to study whether a monoclonal anti-BSF-1 antibody was capable of inhibiting a mouse polyclonal IgE response to infection with the nematode parasite Nippostrongylus brasiliensis (Nb) or to injection of an affinity-purified goat anti-IgD (GaM8). Results of these studies indicate that anti-BSF-1 antibody substantially inhibits IgE but not IgG1 secretion in these mice and thus strongly suggest a specific and important role for BSF-1 in the physiologic stimulation of IgE responses.MATERIALS AND METHODS Animals. Female BALB/c and male athymic nude mice were obtained from the National Institutes of Health Small Animals Division (Bethesda, MD) and were used at 8-12 weeks of age.Antibodies. Affinity-purified GaM8 (20), rabbit antibody specific for the e chain of mouse IgE (RaME) (9), and alkaline phosphatase conjugated to affinity-purified, mouse serumabsorbed, goat anti-rabbit immunoglobulin (21) were prepared. The rat-mouse hybri...

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Anti-cytokine antibodies that block interactions between cytokines and cytokine receptors have been used to inhibit endogenous cytokine function. However, injection of mice with mixtures of IL-4 and either of two neutralizing anti-IL-4 mAb, at a cytokine/anti-cytokine mAb molar ratio of approximately 2:1, enhances and prolongs in vivo IL-4 activity, as measured by induction of increased spleen cell Ia expression. Although splenocyte Ia expression returns to baseline two days after mice are injected with free IL-4, soluble IL-4-anti-IL-4 mAb complexes still induce several-fold increases in Ia expression 3 days after injection. Complexes that contain as little as 400 ng of IL-4 have considerable in vivo stimulatory activity, and a maximal effect on splenocyte Ia expression is induced by injection of 2 micrograms of complexed IL-4. The stimulatory effect of IL-4-containing complexes on splenocyte Ia expression can be blocked by increasing the ratio of anti-IL-4 mAb to IL-4, by injection of anti-IL-4R mAb, and by in vivo aggregation of the complexes. Complexes of IL-4 with a non-neutralizing anti-IL-4 mAb do not have increased IL-4 agonist activity in vivo. These observations are most consistent with the possibility that neutralizing anti-IL-4 mAb act as carrier proteins that increase the in vivo half-life of IL-4 by preventing its excretion, and possibly, by preventing modification of its active site. The enhanced agonist effect of IL-4-anti-IL-4 mAb complexes is not unique; complexes of IL-3 with a neutralizing anti-IL-3 mAb have a greatly increased ability, compared with free IL-3, to stimulate mucosal mastocytosis, and complexes of IL-7 with a neutralizing anti-IL-7 mAb have a greatly increased ability, compared with free IL-7 or IL-7 complexed with a non-neutralizing anti-IL-7 mAb, to stimulate an increase in pre-B cell number. These observations suggest that complexes of cytokines and neutralizing anti-cytokine mAb may provide a generally useful way to increase the magnitude and duration of cytokine effects in vivo.

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Stimulation of B lymphocytes through the Ig receptor initiates a cascade of biochemical changes, which can ultimately lead to either activation and growth, or cell-cycle arrest and cell death. One of the critical events that occurs in both cases is the activation of tyrosine kinases, and the resulting phosphorylation of a variety of proteins on tyrosine residues. In this report we identify one of the substrates of phosphorylation as the 85-kD subunit of the enzyme phosphatidylinositol-3 kinase (PI3K), and show that both anti-IgM and anti-IgD stimulation results in an increase in the anti-phosphotyrosine-precipitable PI3K activity. Furthermore, we show that the potent and specific inhibitor of PI3K, Wortmannin, can completely abrogate anti-Ig-mediated growth inhibition without affecting tyrosine kinase induction or protein kinase C (PKC) activation. Treatment of intact cells with Wortmannin results in an irreversible decrease in anti-Ig-induced PI3K activity, suggesting that the effect of Wortmannin on anti-Ig-mediated growth inhibition is caused by its inactivation of PI3K activity. Taken together, these data show that activation of PI3K is a critical component of the anti-Ig-initiated signaling cascade that leads to growth inhibition of human B lymphoma cells.