Lymphocytes bearing Fc receptor for IgE. VIII. Affinity of mouse IgE for Fc epsilon R on Mouse B lymphocytes.

Fc epsilon R(+) lymphocytes were demonstrated in BALB/c, C57BL/6 and SJL strains of mice by a rosetting technique. The proportion of Fc epsilon R(+) lymphocytes in their spleens was 25 to 33% of the total cells. The majority of the Fc epsilon R(+) cells in the spleen of BALB/c mice were B cells, which also have Fc gamma R. However, after infection of mice with Nippostrongylus brasiliensis, a significant proportion of T cells also bore Fc epsilon R. The average number of Fc epsilon R per Fc epsilon R(+) cell in normal BALB/c spleens was 5100. These receptors were saturated with IGE after incubation of the cells with 5 micrograms/ml mouse IgE. The forward rate constant (k1) of the IgE binding to Fc epsilon R on normal B cells was 1.66 X 10(4) M-1 sec-1, while the dissociation rate of IgE from the Fc epsilon R was 1.7 x 10(-4) sec-1. The equilibrium constant between mouse IgE and Fc epsilon R on normal B cells was approximately 0.95 X 10(8)M-1. However, Fc epsilon R on mouse lymphocytes appeared to be heterogeneous with respect to their affinity for IgE. After infection of mice with Nippostrongylus brasiliensis, the number of Fc epsilon R per receptor-bearing lymphocyte increased several-fold. The FC epsilon R newly expressed after infection appeared to have a lower affinity for IgE than those present originally.