A cross-reaction betwen β₂-microglobulin and kappa light chains

Certain antisera to immunoglobulins containing kappa chains show the presence of antibodies that cross-react with β₂-microglobulin. This was most apparent with an antiserum made to highly purified F(ab) fragments of Fr II γ-globulin. These cross-reactive antibodies caused positive fluorescence and cytotoxicity reactions with a variety of cell types including T cells. These reactions were completely removed by absorption with highly purified kappa chains but not with λ-chains or λ immunoglobulins. β₂-microglobulin preparations also absorbed or inhibited the special cellular reactivities. Evidence was obtained that HLA-bound β₂-microglobulin was more efficient in this respect. The possibility is discussed that similar cross-reactive antibodies may have been involved in some previous studies of inhibition of T cell function by immunoglobulin antisera.