MGI:96213CBA, C3H, DBA/2, SM and AKR have the F.1 form of this soluble liver antigen; A/J, A2G, BALB/c and C57BL/10 the F.2 form. F.2 antigen induces precipitating antibodies in F.1 but not F.2 strains and vice versa. F antigen immune response requires H2 Kk or Ak alleles.