Abstract
To the Editor: Human granulocytic anaplasmosis (HGA) is an emerging tick-borne infectious disease caused by Anaplasma phagocytophilum, an obligatory intracellular bacterium (1). Recently, 2 cases of HGA were identified by a retrospective study in Japan (2). For serodiagnosis of HGA, A. phagocytophilum propagated in HL60 cells is usually used as an antigen, especially by indirect immunofluorescent assay (IFA) (3). However, the serum from these 2 patients in Japan reacted with antigens of A. phagocytophilum cultured in THP-1 cells rather than in HL60 cells in IFA (2). In A. phagocytophilum, a p44/msp2 multigene family encoding multiple 44-kDa immunodominant major outer membrane protein species (so-called P44) exists on the genome, and these multigenes are similar, but not identical, to each other, and the bacterium generates antigenic variations because of gene conversion (4). The previous studies showed that A. phagocytophilum expresses predominantly 2 species of p44/msp2 transcripts in THP-1 cells, but it produces the variation of P44 protein species in HL60 cells (2,5). This finding strongly suggested that A. phagocytophilum grown in THP-1 cells differs serologically from that in HL60 cells. Our serologic analysis found 4 recent cases of HGA in Japan by using infected THP-1 and HL60 cells as antigens, and some P44 immunoreactive protein species of A. phagocytophilum that were associated with the respective cell line cultures, binding to antibodies from the 4 patients’ serum, also were identified.
Highlights
To the Editor: Human granulocytic anaplasmosis (HGA) is an emerging tick-borne infectious disease caused by Anaplasma phagocytophilum, an obligatory intracellular bacterium [1]
In immunofluorescent assay (IFA) tests for HGA, IgM and/or IgG from the patients’ serum samples reacted with A. phagocytophilum cultured in THP-1, HL60, or both, and the seroconversions were observed in convalescent-phase serum from all patients
Western blot analysis further confirmed the specific reaction to P44 protein antigens (P44s) of A. phagocytophilum cultured in THP-1 and HL60 and to recombinant P44–1 protein in the serum samples, supporting the IFA results in the Table
Summary
To the Editor: Human granulocytic anaplasmosis (HGA) is an emerging tick-borne infectious disease caused by Anaplasma phagocytophilum, an obligatory intracellular bacterium [1]. Our serologic analysis found 4 recent cases of HGA in Japan by using infected THP-1 and HL60 cells as antigens, and some P44 immunoreactive protein species of A. phagocytophilum that were associated with the respective cell line cultures, binding to antibodies from the 4 patients’ serum, were identified. Western blot analysis further confirmed the specific reaction to P44 protein antigens (P44s) of A. phagocytophilum cultured in THP-1 and HL60 and to recombinant P44–1 protein (rP44–1) in the serum samples (online Technical Appendix Figures 1 and 2), supporting the IFA results in the Table. Patients’ serum reactive with A. phagocytophilum cultured in HL60 cells in IFA bound to rP44–18ES (online Technical Appendix Figure 4; Table) This finding strongly supports the results of IFA and Western blot analyses with the infected THP-1 and HL60 cells. Our study provides substantial information about the usefulness of suitable P44 immunoreactive protein species of A. phagocytophilum as antigens for serodiagnosis of HGA
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