Identification of a new white cell antigen

BACKGROUND: Antibodies to white cell antigens can cause alloimmune neonatal neutropenia, autoimmune neutropenia, and transfusion reactions. CASE REPORT: A full-term male infant developed a skin infection and was found to be neutropenic on his fourth day of life. He had a transient increase in his neutrophil count after treatment with intravenous immunoglobulin, but his neutrophil count was not consistently normal until he was 6 weeks old. Serum from the baby's mother reacted in a granulocyte immunofluorescence assay but not in a granulocyte agglutination assay. The mother's serum was tested in the granulocyte immunofluorescence assay against neutrophils from 103 healthy, unrelated people, and it reacted with cells from 66 percent of those people. The expression of SL correlated weakly with the expression of NA1 (r = 0.23; p = 0.02) and 5a (r = 0.20; p = 0.05) antigens. SL antigen expression on neutrophils was not associated with the expression of NA2, NB1, NB2, NC1, 5b, 9a, or Mart. The expression of SL on neutrophils from members of an extended family was analyzed, and the antigen was found to be inherited in an autosomal-dominant manner. Anti-SL also reacted with T-lymphocytes in a flow cytometry assay but did not react with red cells or platelets. No lymphocytotoxic antibodies were detected in the mother's sera. The anti-SL was tested against neutrophils in an immunoprecipitation and immunoblotting assay, but no molecules were identified. The neutrophil-specific antigens NA are located on Fc gamma receptor III (CD16). To determine if the SL antigen was also located on Fc gamma receptor III, anti-SL was also tested in a monoclonal antibody immobilization of granulocyte antigens assay. Anti-SL did not react with molecules recognized by CD16 monoclonal antibodies. CONCLUSION: A new white cell antigen SL, with a frequency of 66 percent, was identified on neutrophils and T- lymphocytes as a result of the evaluation of a case of neonatal alloimmune neutropenia. The molecule bearing the SL antigen was not identified in immunoblotting, immunoprecipitation, or monoclonal antibody immobilization of granulocyte antigens assays.