Quantitation of D sites on selected 'weak D' and 'partial D' red cells.

Measurements have been made of the number of available sites on 10 examples of red cells in which the only abnormality appeared to be a quantitative reduction in the expression of D (weak D cells); these estimates were carried out using three monoclonal anti-D antibodies, Fog-1, Brad-3 and Los-2. The values varied with the monoclonal antibody that was used and fell within the range of 170-1,870 sites/cell. A further 3 examples of weak D cells which had brought about immunisation following transfusion were found to have between 390 and 1,470 sites per red cell. The implications of the D site density on the immunogenicity of weak D cells are discussed. The number of sites on red cells with structurally abnormal D (partial D cells) were also estimated, using the antibody Fog-1. Four of the 5 examples of cells of category IVa (probable phenotype Ror) were found to have a high expression of D (range 29,300-41,300), but the available D sites of categories DVa, DVIa, and DVII were considerably reduced (< 500, < 500 and 2,400-7,500 sites/cell, respectively). As a working hypothesis, it is suggested that there are two types of genetic abnormality leading to an abnormal expression of D. First, a defect in genomic DNA leading only to a quantitative reduction in the number of available D sites; this genomic lesion should be termed 'weak D'. Secondly, genomic defects leading to amino acid sequence abnormalities and structural change in the D polypeptide; these lesions should be collectively known as 'partial D'.

Further characterisation of a human monoclonal antibody to the rhesus D antigen produced in vitro.

UCH D4 is a human monoclonal antibody produced by an Epstein-Barr (EB) virus-transformed lymphoblastoid cell line. The antibody is specific for the rhesus D antigen, and is a good laboratory reagent for red blood cell typing. UCH D4 can be purified from the culture supernatant medium with the removal of all detectable DNA and infectious EB virus particles. This purified antibody will be used for in vivo assessment of its ability to prevent Rhesus disease of the newborn.