HL‐A Immunization and HL‐A Types in Pregnancy

A total of 199 pregnant women with lymphocytotoxic antibodies in their sera were HL‐A typed and the specificities of their antibodies were investigated by extensive panel investigations. A tentative classification of related HL‐A antigens was based on (1) the non‐random distributions of positive and negative deviations from Hardy‐Weinberg equilibrium of the LA and FOUR phenotypes of these women; (2) the co‐occurrence of HL‐A specificities in the sera of 139 women whose antibodies could be identified; and (3) the relationship between the LA and FOUR antigens present in these women and the antibodies found in their sera. The antigens HL‐A2, Ba*(W28), and HL‐A9 of the LA series appear to form one group while the remaining antigens of this series may form another. In the FOUR series, two major groups can be postulated: HL‐A5 12 R* (W5) SL‐MaPi(W17), CM(W18), and LND (W15) constitute one group; and HL‐A7,8 BB(W10), FJH(W27), and AA (W22), another. This classification of FOUR antigens is similar but not entirely identical to the one obtained by anti‐4a and anti‐4b sera. Immunization against FOUR antigens was more frequent than against LA antigens, and this superior antigenicity of FOUR antigens was evident also when taking into account the chances of these women to meet the antigens during varying numbers of pregnancies and transfusions.