Depression of grass pollen-induced lymphocyte transformation by serum from hyposensitized patients.

Serum from grass-sensitive patients who had received hyposensitization therapy was found able to depress the in vitro response to Holcus lanatus grass pollen extract of lymphocytes from untreated grass-sensitive individuals. The inhibitory activity could no longer be demonstrated at serum dilutions equal to or greater than 1/100 and was not seen when the cells were stimulated with PHA or unrelated antigens. It was contained in the precipitated fraction of 33% saturated ammonium sulphate-treated serum, segregated with the 7S peak of Sephadex G-200 and with the IgG fraction of DEAE-Sephadex-fractionated serum and could be removed by the absorption of the serum with the Holcus lanatus allergenic extract. These data suggest that the serum factor responsible for the depressed in vitro lymphocyte response to the allergen in hyposensitized patients was a 7S IgG antibody induced by immunotherapy.