Sialyl-Lewis x-Independent Infection of Human Myeloid Cells by Anaplasma phagocytophilum Strains HZ and HGE1

ABSTRACT Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis, is an obligate intracellular bacterium that infects neutrophils and neutrophil precursors. Bacterial recognition of P-selectin glycoprotein ligand-1 (PSGL-1) and the α2,3-sialylated- and α1,3-fucosylated-moiety sialyl-Lewis x (sLex), which modifies the PSGL-1 N terminus, is important for adhesion to and invasion of myeloid cells. We have previously demonstrated that A. phagocytophilum organisms of the NCH-1 strain that utilize an sLex-modified PSGL-1-independent means of entry can be enriched for by cultivation in undersialylated HL-60 cells that are unable to construct sLex. Because it was unknown whether other A. phagocytophilum isolates share this ability, we extended our studies to the geographically diverse strains HZ and HGE1. HL-60 A2 is a clonal cell line that is defective for sialylation and α1,3-fucosyltransferase. HL-60 A2 cell surfaces, therefore, not only lack sLex but also are virtually devoid of any other sialic acid- and/or α1,3-fucose-modified glycan. By cultivating HZ and HGE1 in HL-60 A2 cells, we enriched for bacterial subpopulations (termed HZA2 and HGE1A2) that bind and/or infect myeloid cells in the absence of sialic acid and α1,3-fucose and in the presence of antibody that blocks the N terminus of PSGL-1. Thus, multiple A. phagocytophilum isolates share the ability to use sLex-modified PSGL-1-dependent and -independent routes of entry into myeloid cells. HZA2 and HGE1A2 represent enriched bacterial populations that will aid dissection of the complexities of the interactions between A. phagocytophilum and host myeloid cells.