Frequency of HLA-DP-specific antibodies and a possible new cross-reacting group.

Clinical studies have demonstrated that HLA-DP-specific antibodies can be detrimental to a transplanted kidney. The number of patients affected is proportional to the frequency of DP antibodies. We determined the frequency of HLA-DP-specific antibodies en toto and in the absence of cross-reactive DR antibodies. Of 650 waitlisted renal patients, 271 (42%) were reactive with HLA-DP antigens in solid-phase immunoassays. Of these 271 sera, 58 (21%) were negative for reactivity with cross-reactive DR antigens, and 16 (5.9%) had no class II antibody other than DP. Eliminating sera containing DR cross-reactive antibodies reduced the frequency but not the overall strength of DP antibodies. Although most DP antibodies were not expected to yield a positive cytotoxicity crossmatch, 2 DP-specific antibodies yielded cytotoxic crossmatch tests with titers of >512. The occurrence of HLA-DP-specific antibody differed significantly between previously transplanted (62%) and nontransplanted (38%) patients, but no difference was observed among patients categorized by race or sex. One serum demonstrated strong cross-reactivity between DP and DRB1*01:03 in the absence of DR1 or DR11 reactivity. Sequence alignments were performed and a possible new cross-reactivity between DRB1*01:03 and DP2, DP9, DP10, DP13, DP16, and DP17 was defined. Two additional sera confirmed this cross-reactivity.