Primate HLA Antibodies are Specifically Mitogenic for Human Lymphocytes and Act Synergistically with β2m Antibodies

A monkey antiserum against HLA-A28 was raised by immunization with papain-solubilized antigens. The titre of this serum was 1/370 for beta2-microglobulin (beta2m) 1/750 for A28 and 1/200 for the cross-reacting HLA-A2 determinant. This serum was highly mitogenic for human blood lymphocytes. Mitogenicity was reduced or abolished after absorption of the serum on a beta2m-spharose column. Column-eluted anti-beta2m antibodies were not mitogenic. However, mitogenicity was restored by reconstitution with unabsorbed and absorbed antibodies. Mitogenicity was target cell specific. Tuhs, cells from all individuals were activated by the unabsorbed serum. The absorbed anti-A28 serum was mitogenic only for target cells carrying A28 and/or the cross-reacting determinant A2, but not for cells lacking either of these antigens. A definite gene-dose effect was recorded, since target cells homozygous for A2 responded better to polyclonal activation by the primate serum than cells which were heterozygous.