IgE and IgG subclass regulation by IL-4 and IFN-gamma in human helminth infections. Assessment by B cell precursor frequencies.

Helminth infections, like atopic disorders, show characteristic elevations of serum IgE and IgG4. To examine the mechanisms underlying the regulation of these two isotypes and of the other IgG subclasses, the frequency (Fo) of isotype-specific B lymphocytes (Bc) from 11 patients with helminth infections was compared by filter-spot ELISA using fresh peripheral blood-derived lymphocytes after 14-day Ag stimulation in vitro. The role of IL-4 and IFN-gamma in the generation and regulation of Ag-driven isotype responses was determined. The Fo of freshly obtained lymphocytes (expressed/10(5) Bc) secreting polyclonal Ig for the following isotypes was: IgE (geometric mean = 0.72; range, 0 to 17.7); IgG4 (geometric mean = 4.9; range, 1.8 to 24.4); IgG1 (geometric mean = 134.3; range, 16.7 to 318). The Fo of IgE correlated with IgG4-secreting Bc among study subjects (r = 0.8, p < 0.01), however there was no association with the other isotypes. Parasite Ag added to cultured lymphocytes induced significant expansion in the number of Ig-secreting Bc for IgE and all IgG subclasses. In contrast, addition of a nonparasite Ag, tetanus toxoid, generated increased Fo of Ig-secreting Bc for IgG1, IgG2, and IgG3, and no expansion of IgG4 or IgE. The essential role of IL-4 in the expansion of IgE- and IgG4-secreting B cells in response to filarial Ag was demonstrated when simultaneous addition of neutralizing anti-IL-4 antibodies completely inhibited this response in all 11 patients studied. Neutralizing anti-IL-4 had no effect on either filarial or tetanus toxoid-driven expansion of IgG1-, IgG2-, or IgG3-secreting Bc. An inhibitory role of endogenously produced IFN-gamma was also shown when addition of neutralizing anti-IFN-gamma to cultures significantly augmented Ag-driven expansion of Bc-secreting IgE and all IgG subclasses; IgE, 0.4- to 9-fold; IgG4, 1.4- to 12-fold; IgG1, 1.6- to 13-fold; IgG2, 1.9- to 5-fold; and IgG3, 2.7- to 6-fold. This study demonstrates that parasite Ag stimulates Bc expansion in helminth-infected patients. Although this response for all five isotypes studied is down-regulated by IFN-gamma, the generation of only the IgE and IgG4 responses appears to be mediated selectively by IL-4. These findings support the concept that IgE and IgG4 production are linked and related to the quantities of IL-4 and IFN-gamma induced by Ag-specific T cells.