“Cleaved Lymphocytes” Could Be Induced by Pertussis Toxin Injection in Mice, and Are Actually Not Lymphocytes

To the Editor—With great interest we read the most recent contribution of Zhang et al reporting that a simple blood smear may provide a diagnostic clue for Bordetella pertussis infection [1]. Zhang et al described a case of pertussis with peripheral blood smear showing mature lymphocytes with cleaved nuclei, characteristic of B. pertussis lymphocytosis. As the authors state, this finding provides a possibly easy and new way to determine pertussis, because current laboratory tests, such as isolation of B. pertussis and detection of its bacterial DNA, are not widely available. Their results were also supported by other 2 previous reports published in Blood [2] and The Lancet Infectious Diseases [3]. However, there were several questions about these "cleaved lymphocytes." Can these cells occur in the blood after the pertussis toxin (PT) injection? PT is a specific toxin of B. pertussis and is the cause of lymphocytosis [4]. If true, cleaved lymphocytes could be a clue to suspect pertussis. In addition, do the cleaved lymphocytes belong to lymphocytes? After all, their morphologic characteristics are obviously different from normal lymphocytes.