SEROLOGIC SUBTYPING OF HLA-DR8 BY MEANS OF THE CYTOTOXIC HUMAN MONOCLONAL-ANTIBODY-5643

EBV-transformed B cells from a multiparous woman with anti-HLA antibod ies were hybridized with CB-F7 heteromyeloma cells. The resulting hybr idoma produced the cytotoxic human IgM(kappa) mAb 5643. Testing of the hybridoma supernatant against HLA homozygous cell lines demonstrated positive reactions (titer range 128-512) only with three cell lines th at carried the DR (alpha,beta 1()0801) subtype of DR8. There was no r eaction with cells expressing other variants of DR8; i.e., carrying th e DR beta 1()0802, 0803, or 0804 chains. The only difference between the DRB1();0801 and DR beta 1(*)0802/0804 chains and between the DR b eta 1()0801 and 0803 chains is a single aa substitution, a Ser-->Asp substitution at residue 57 and a Phe-->Ile substitution at residue 67, respectively. Residues 57 and 67 are both situated on the alpha-helix of the DR beta chain. The distance between residues 57, and 67 is two full turns of the alpha-helix; i.e., about 1 nm. It is possible that both 57 Ser and 67 Phe are directly involved in the epitope recognitio n by mAb 5643.