The effect of serum factors on Ig synthesis (IgE, IgG) in vitro was analyzed. Spleen and mesenteric lymph node cells were obtained from Nippostrongylus brasiliensis-infected and non-infected mice. Sera and ammonium sulphate precipitated serum fractions from mice of different genetic origin (Balb/c - H-2d, A.CA - H-2f, B10.G - H-2q) suppressed in vitro IgE synthesis whereas a pronounced enhancement of IgG antibody synthesis was obtained in several experiments. Our results obtained with sera from both high and low IgE responder strains demonstrated that no strain specificity exists as to the inhibitory efficacy of mouse sera for total IgE synthesis in vitro. The suppressive activity of the mouse sera was concentrated in a fraction precipitated with 20%-50% saturated ammonium sulphate. Amicon XM50 ultrafiltration suggested that this fraction had an apparent molecular weight greater than 50,000 daltons. Suppressive activity was removed by immunoadsorption of the 20-50% fraction with anti-IgE Sepharose. After exogenous addition of monoclonal IgE to an inactive fraction in vitro neither the fraction enriched in IgE nor monoclonal IgE alone were able to suppress IgE synthesis in the culture. Our results suggest that one or more serum factors in the presence of IgE are responsible for the suppression of total IgE synthesis in vitro.

In vitro IgE synthesis by lymphoid cells was studied during the course of infection of mice with Nippostrongylus brasiliensis. The studies involved inbred strains of mice which had been shown to be high IgE responders (A.CA, B10.M), or non-responders (Balb/c, B10.D2) to parasite antigen. In addition, F1 hybrids of low and high responders and irradiated non-responders were studied. Infection with N. brasiliensis led to an increase in IgE synthesis in vitro which was most pronounced during reinfection of mice. Addition of mitogens e.g. pokeweed mitogen (PWM), lipopolysaccharide (LPS), concanavalin A (ConA) to the cultures induced enhancement, suppression or had no effect on IgE synthesis. Addition of N. brasiliensis homogenate or worm culture supernatant led to a fluctuating pattern of IgE synthesis. No correlation was found between lymphocyte proliferative response to mitogen and worm antigens and IgE synthesis. Our data suggest, that PWM is more likely to enhance IgE synthesis in vitro than LPS or ConA. An enhancement is more easily observed with the cells of non-infected animals or during the early phase of infection or reinfection. The mitogen-induced increase in IgE synthesis did not exceed the values obtained during infection or reinfection.

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Generation of IgE-specific suppressor factors in vitro upon stimulation of murine lymphocytes with IgE was studied. High-molecular weight factors (>50 kilodalton) suppressed in vivo IgE response as well as de novo IgE synthesis in vitro. Further, suppression of IgE synthesis in vitro by fractions of low molecular weight supernatants absorbed with IgE-Sepharose was obtained, suggesting a potent role for IgE binding factors in IgE synthesis.

Modulation of de novo IgE synthesis in vitro was studied using the parasitic infection of mice with the nematode Nippostrongylus brasiliensis. Cell-derived factors were generated by stimulation of splenic and mesenteric lymph node cells of BALB/c mice with monoclonal IgE in vitro. High molecular weight (greater than 50,000) and low molecular weight (less than 50,000) culture supernatants were prepared. De novo IgE synthesis of BALB/c lymphocytes--obtained from N. brasiliensis-reinfected mice that secreted pronounced quantities of IgE in vitro--was markedly reduced by the addition of high molecular weight supernatants. A dose-dependent suppression of IgE synthesis was obtained, whereas IgG synthesis, viability, and cell proliferation were not inhibited. After fractionation of low molecular weight supernatants with IgE-Sepharose the glycine/HCl eluate fractions markedly inhibited the in vitro IgE synthesis. Low molecular weight factors which suppressed IgE synthesis without modulating IgG production were obtained from IgE high responder B6D2F1 normal mouse cells. Thus, our results demonstrate the generation of IgE-specific suppressor factors in vitro upon stimulation with IgE. The suppression of IgE synthesis by eluate fractions of low molecular weight supernatants absorbed with IgE-Sepharose suggest a potential role for IgE binding factors on de novo IgE synthesis in vitro.