Light chain phenotypes of HLA antibodies in cases with suspected neonatal alloimmune thrombocytopenia

Abstract

Platelet-specific antibodies are detectable in only about 30% in suspected neonatal alloimmune thrombocytopenia (NAIT). Human leucocyte antigen (HLA) class I antibodies are often detectable, and as platelets express the corresponding antigens, it has been suggested that these antibodies can be responsible for NAIT. Light chain phenotyping may assist in the diagnosis of HLA antibodies-induced NAIT. We determined light chain phenotypes of platelet reactive HLA antibodies in 17 sera from mothers who delivered offspring with suspected NAIT. Ten sera also contained platelet-specific antibodies: HPA-1a (n = 5, one with HPA-15b), HPA-5b (n = 4) and autoantibodies (n = 1). Sera were tested for kappa or lambda restriction by monoclonal antibody-specific immobilization of platelet antigens (MAIPA). The cross-match with paternal platelets was positive in all cases due to HLA antibodies. We identified 5, 3 and 3 sera to contain lymphocytotoxic antibodies of single, two or multiple specificities, respectively. In six cases, HLA antibodies were only detectable by MAIPA. Light chain restriction (n = 9) was not associated with HPA containing antibodies or to any pattern of the HLA antibodies. Similarly, polyclonal antibodies (n = 8) were seen in all categories. We show that pregnancy-associated HLA antibodies can be clonal or polyclonal, irrespective of a diagnosis of NAIT. ONE-SENTENCE SUMMARY: Pregnancy associated HLA antibodies can be clonal or polyclonal, irrespective a diagnosis of NAIT.