Inhibition of K cell function by human breast cancer sera

Sera from breast cancer patients and from female controls were tested for inhibition of lysis of antibody-coated target cells by human leukocytes (K cells). Sera from 39% of breast cancer patients, but from only 8% of controls, inhibited lysis by more than 30%. This inhibition was unrelated to the stage of the disease, the patient's age or whether the patient was pre- or post-operative. Inhibition was apparently not due to anti-HLA antibodies and did not correlate with the IgG level or anti-complementary activity of the serum. On fractionation by gel-filtration, inhibitory activity was found in fractions of higher molecular weight than IgG. As no IgG could be detected in these fractions, inhibition is probably not due to immune complexes containing IgG antibody. The inhibitory factor may well contribute to the immunosuppressed status of a proportion of breast cancer patients.