Anti‐Sp₁: The Recognition of a New Cold Auto‐Antibody

Summary. Cold auto‐antibodies reacting with an antigen that appears to be independent of the Ii system are described. No human blood sample lacking the reacting antigen (designated Sp₁) could be found but the common serological behaviour suggests that the antisera form a homogeneous group. The evidence suggests that these antibodies may be directed against a basic species antigen common to all human cells.