Platelet immunofluorescence, together with other serologic tests on platelets, lymphocytes, and granulocytes, was used to investigate the sera of 38 mothers with newborns who suffered from
thrombocytopenia. In sera of 33 mothers, platelet-specific
IgG alloantibodies were demonstrable. Three sera also contained HLA
antibodies, of which two were only detectable in the lymphocyte cytotoxicity test. Two other sera contained granulocyte-specific
alloantibodies. In sera of 2 mothers,
antibodies were found that reacted with all cell types in all tests. However, after further analysis, it became clear that platelet-specific
alloantibodies were probably also present in these 2 sera. In 29 cases, the specificity of the platelet
alloantibodies was anti-Zwa--PlA1. One serum contained
antibodies directed against a new
antigen, Baka. This new
antigen was defined after the investigation of the family and a small-scale population study. Two other sera had platelet
antibodies with still undefined specificities. In all positive sera,
IgG platelet
alloantibodies were detected, and sometimes
IgM antibodies were also present. The
IgG antibodies were mostly of the
IgG1 subclasses, but sometimes
IgG3 and/or
IgG4 was also found. In a few sera, only
IgG3 antibodies were detected. In our series, we found no increased frequency of
blood group ABO compatibility between mother and child, although it has been described by others and is well known to occur in rhesus alloimmunization. Of all the tests used, the platelet immunofluorescent test, especially the test on
paraformaldehyde-fixed platelets in
suspension, gave the best results in the detection of platelet
antibodies in
neonatal alloimmune thrombocytopenia.